Reaction of 3-halogeno-2H-1-benzopyran-2-ones with organometallic compounds. Synthesis of 4-Alkyl-2H-1-benzopyran-2-ones. X-Ray molecular structure of 3-bromo-3,4-dihydro-4-isopropylcoumarin

摘要

J. CHEM. SOC. PERKIN TRANS. 1 1991 Reaction of 3-HaIogeno-2H-1- benzopyra n-2-ones with 0rga nometa IIic Compounds. Synthesis of 4-Alkyl-2H-1 -benzopyran-2-ones. X-Ray Molecular Structure of 3-Bromo-3,4-d i hydro-4- isopropylcoumarin Angel Alberola,' Blanca Calvo,' Alfonso Gonzalez Ortega,*na Martina Vicente,a Santiago G. Grandab and Juan F. Van der Maelenb a Departamento de Quimica Organica, Universidad de Valladolid, Spain Departamento de Quimica Fisica y Analitica, Facultad de Quimicas, Universidad de Oviedo, Spain 3-Halogeno-2H-I -benzopyran-2-ones react with magnesium, lithium, aluminium and copper derivatives to give 3,4-dihydrocoumarins and 3- (0-hydroxyphenyl) propenols as major products. The nature and the ratio of the products in the final mixture depend on the solvent and on the organometallic reagent.Grignard derivatives yield 1,4-monoalkylation compounds in tetrahydrofuran (TH F) or 1,2-dialkylation derivatives in toluene. In some cases the dehalogenation competes with the 1,2-alkylation process in the reactions with alkyllithiums. The presence of the halogen at C-3 increases the reductive ability of organoaluminiums. In general, the reaction with lithium dialkylcuprates leads to complex mixtures of products. The 4-alkyl-3-halogeno-3,4-dihydrocoumarins obtained undergo dehydrohalogenation easily, and lead to 4-alkylcoumarins in good yields. The tandem alkylation-dehydrohalogenation of 3- halogeno-2H-I -benzopyran-2-ones constitutes a versatile synthesis of 4-alkylcoumarins. The reaction of coumarins with organometallic compounds is a very well known synthetic method to 2H-1-benzopyrans.We have now studied the reactivity of 3-chloro- and 3-bromo- coumarins towards magnesium, lithium, aluminium and copper derivatives in order to confirm the influence of the halogen on the behaviour of these substrates. The Grignard derivatives react with 3-chlorocoumarin 1, 3-bromocoumarin 2, and 3-bromo-4-methylcoumarin 3 leading to dihydrocoumarins, chromen-2-ols, and open-chain compounds as a consequence of 1,4- and/or 1,2-addition or reduction processes (Scheme 1). The rate of reaction is intermediate between that with the organolithiums and that with organo- aluminiums, and the solvent plays an important role in deter- mining the ratio of the products in the final mixture (Table 1).As previously described for 3-phenyl- and 3-ethoxycarbonyl- ~oumarin,'-~in our case the 1P-addition process was favoured when the reactions were carried out in ether solvents (THF or diethyl ether) and with increasingly bulky groups R; the result- ing 4-alkyl-3-halogeno-3,4-dihydrocoumarins4 and 5 were obtained as a mixture of cis (80-90%) and trans (20-10%) isomers. 1 X=CI,R'=H 4 X=CI 6 2 X=Br,R'=H 5 X=Br3 X = Br, R'= Me Indeed a double 1,2-addition was the major process for 3- bromo-4-methylcoumarin or when benzene or toluene was used as solvent. The ratio of products in the final mixture also depends on the nature of the magnesium derivative; thus, EtMgI and EtMgBr led to the same mixture, but MeMgI did not produce 1,4- addition, and Pr'MgBr gave reduction products (E)-2-bromo- 1- (o-hydroxyphenyl)-4-methylpent-l-en-3-01 12d and (E)-2-chloro-l-(o-hydroxyphenyl)-4-methylpent-1 -en-3-01 1Id in 5s 60% yield.On the other hand, 3-chloro- and 3-bromo-coumarin behave in similar fashion towards organometallics. Only in the case of phenylmagnesium bromide did 3-bromocoumarin lead to phenyl2,3-dihydro-3-phenylbenzofuranylketone 7f, whereas 3-chlorocoumarin yielded 3-chloro-3,4-dihydro-2,4-diphenyl-2H-l-benzopyran-2-016f, but both products derive from a common hydroxy ketone (acyloin) intermediate 6' that in the hydrolysis leads to the benzofuran 7 derivative-if X = Br-or to the chromanol-if X = Cl-(Scheme 2).As an alternative to the preparation of compounds 4a, 5a, 4f and 5f we have tested the reactivity of compounds 1 and 2 with OH 7 8 + R' 15 13 X=CI 14 X=Br 11 X=CI 12 X=Br 9 X=CI,R'=H 10 X = Br, R' = H 16 X = Br, R' = Me Scheme 1a, R = Me; b, R = Et; c, R = Bu; d, R = Pr'; e, R = Bu'; f, R = Ph. Reagents: i, organometallic compounds; ii, water 204 J. CHEM. SOC. PERKIN TRANS. 1 1991 Table 1 Reaction of compounds 1,2 and 3 with Grignard derivatives Yield (%) Coumarin RMgX Solvent a 4 5 6 7 9 10 11 12 ~~ 1 MeMgI Et,O-PhMe 9a 85 1 EtMgBr Et,O-PhMe 4b 55 9b 40 1 EtMgBr PhMe 4b 25 9b 70 1 EtMgBr Et,O 4b 70 9b 25 1 EtMgI Et,O 4b 75 9b 20 1 BuMgBr PhMe 4c5 9c 85 1 BuMgBr Et,O 4c 40 9c 50 llc 5 1 BuMgBr THF 4c 65 9c 20 llc 15 1 Pr'MgBr Et,O-PhMe 4d 65 9d 15 llc 15 1 Pr'MgBr PhMe 4d 20 9d 20 lld 57 1 Pr'MgBr Et20 4d 25 9d 42 lld 30 1 PhMgBr Et,O-PhMe 6f 20 9f 60 b 2 MeMgI Et,O-PhMe 1Oa 80 2 EtMgBr Et,O-PhMe 5b 40 10b 52 b 2 EtMgBr PhMe 5b 27 lob 65 b 2 EtMgBr THF 5b 66 10b 30 b 2 EtMgBr Et20 5b 40 10b 52 h 2 BuMgBr PhMe 5c 12 1Oc 70 12c 14 2 BuMgBr THF 5c 72 1oc 20 2 Pr'MgBr Et20-PhMe 5d 60 IOd 22 12d 16 Pr'MgBr PhMe 5d 24 10d 16 12d 56 Pr'MgBr Et,O 5d 70 1Od 12 12d 10 PhMgBr Et,O-PhMe 7f 60 10f 20 C EtMgBr Et20 d ~~ ~~ a The reactions were carried out at 0 "C for 30 min.Compounds 15 (610%) were also isolated. 'Compound 8f (15%) was isolated. 4-Bromo-3-ethyl-5-(o-hydroxyphenyl)hex-4-en-3-0116b (70%) was isolated. OMgBr OMgBr my-a P h 2 ir i,ii \ --1 i or2 1.2 1,4 \ qPh 2 R RPh OMgBr 435I Scheme 3 Ratio of cis:trans isomers: R = Me, 60:40; R = Et, 80:20; R = Bu, 85: 15; R = Pr', 90: 10; Reagents: i, organometallic compound; ii, water aorh the reaction of compound 1with butyllithium, the chromanone 7aphX 4c can be isolated in 30% yield (Table 2).From the reaction IPh bh 8 mixtures when butyllithium was used as reagent, important amounts of dehalogenation compounds could be obtained; this 6 X=CI 6' behaviour was also observed with magnesium and copper derivatives. (X = Br) It has previously been shown that coumarins suffer a double 1,2-addition towards trialkylaluminiums in hexane, benzene, or t~luene.~.~In the present case, the halogen at C-3 increases the w:h reduction ability of organoaluminiums, with the 1,2-alkylation Ph and 1,2-reduction products 11 or 12 being the major products of the reactions; in the case of triisobutylaluminium, double 1,2- 7 reduction is the most important process (compounds 13 or 14) Scheme 2 Reagents: i, PhMgBr; ii, water (Scheme 4).On the other hand, trimethylaluminium is less reactive than other organoaluminiums, and it requires higher lithium dimethylcuprate and lithium diphenylcuprate; the re- concentrations and reaction times to give moderate yields of actions led to a complex mixture of compounds except for 3-dialkylated diols 9a and 10a (Table 3). chlorocoumarin and lithium dimethylcuprate which yielded The reactivity of organoaluminiums diminished when compound 4a (65%) as a mixture of cis (60%) and trans (40%) diethyl ether or THF were used as the solvent, whereas these isomers.The difference in the ratio of isomers when lithium solvents increased the reductive power; as an example, with the dimethylcuprate and Grignard derivatives were used is a con- system Et,Al-THF compound 13 was obtained 60% yield sequence not of the organometallic reagent's nature but of the (Table 3). stereochemical interactions in the kinetically controlled tauto- The reduction of 3-chloro- and 3-bromo-coumarin with merization of the 4-alkyl-3-halogeno-4H- l-benzopyran-2-01 to DIBAL-H is not a satisfactory method to obtain compounds 13 afford the final product (Scheme 3). and 14. The first step to the hemiacetal intermediate 17 is a Lithium derivatives react with 3-halogenocoumarins to fast process, but its transformation to the final product is very afford 1,2-addition compounds as major products 9 or 10,but in slow at 0 "C.Nevertheless this intermediate is transformed to J. CHEM. soc. PERKIN TRANS. 1 1991 205 Table 2 Reaction of compounds 1 and 2 with lithium derivatives Yield (%) Coumarin RLi Solvent 4 9 10 15 1 MeLi Et20a 9a 80 1 BuLi PhMe 4c 10 9c 80 1 BuLi Et20a 4c 20 9c 70 2 MeLi Et20" 10a 60 15a 25 2 BuLi PhMe 1Oc 60 1% 35 The reactions were carried out at 0 "C. The reactions were carried out at -40 "C. the monoalkylated derivatives 11 and 12, by addition of one equivalent of organolithium or a Grignard derivative (Scheme 5, Table 4).a-i r 1 L -J 13,14 17 Scheme 4 Reagents: i, Bu',Al; ii, water The described monoalkylation process could be achieved from the corresponding coumarin and organoaluminium as previously but the methodology presented here is advantageous because lithium and magnesium derivatives are more easily accessible than are the aluminium ones, and because some of the last substrates showed only reductive (Bu',Al) or alkylation (Me,Al) properties. The yields summarized in Tables 14were determined by 'H NMR spectroscopy on the reaction mixtures. In the Experi- mental section, the yields refer to pure, isolated compounds in optimized experiments. The isomeric mixture of 4-alkyl-3-halogeno-3,4-dihydro-coumarins 4 and 5 was transformed into 4-alkylcoumarins 20 by a base-promoted dehydrohalogenation and the yields and the experimental conditions are summarized in Table 5.The major isomer of the 3-bromo derivatives 5 is easily dehydro- halogenated in pyridine at 50 "C,whereas the minor component is recovered unchanged. Otherwise, 3-chloro derivatives 4 were recovered unchanged after treatment with pyridine in refluxing benzene. Moreover we have been unable to epimerize the mixture to the most stable compound by reaction with Ac20- AcONa; ' 4-alkylcoumarins are obtained from both 3-chloro and 3-bromo derivatives, dehydrohalogenation of the major isomer being easier than that of the minor one. 40r5 -vbase R 20 r ao:X 18 X=CI 11 X=CI 19 X=Br 12 X=Br Scheme 5 Reagents: i, DIBAL-H; ii, water; iii, RMgX or RLi 0 Br(31) 0.Fig. 1 X-Ray structure and crystallographic numbering for com-pound 5d (hydrogen atoms omitted) derivatives 4 and 5 because of the observed systematic be- haviour of their chemical shifts for Ha (Table 6), and their behaviour towards Ac,O-AcNa (Table 5). The cis-configur- ation of the major isomers was corroborated by NOE experi- ments between Ha and Hb, and by the observed anisotropy for methylene protons in 4b and the methyl protons in 4d in their 'H NMR spectra (this anisotropy is higher in 3-chloro than in 3- bromo derivatives). On the other hand, our results are in agreement with those previously described by Ivanov and Bojilova ' for 3-phenyl- coumarin, leading to the less stable cis-isomer assigned by a study on epimerization with Ac,O-AcNa and the coupling cons tan ts.Experimental M.p.s were measured on a Leitz Laborlux D microscope with a heating device and are uncorrected. NMR spectra were re- corded on either Bruker AC80 or Bruker WP200 SY spectro-The cis-configuration of the 3-bromo-3,4-dihydro-4-isoprop-meters and chemical shifts are given downfield from SiMe, as ylcoumarin Sd, determined by X-ray crystallography (Fig. l), internal standard. Mass spectra were measured on a Hewlett- was extended for all the major isomers of the 3-halogeno Packard 5988A mass spectrometer. J. CHEM. SOC. PERKIN TRANS. 1 1991 Table 3 Reaction of compounds 1 and 2 with R,Al" Yield (%) Coumarin R,AI Solvent 9 10 11 12 13 14 Me,Al PhMe 9a 75 Et,Al PhMe 9b 40 llb 55 Et,Al THF 13 65 Bu,Al PhMe 9c 7 llc 85 Bu',Al PhMe llc 40 13 50 Me,Al PhMe 10a 70 Et,Al PhMe 10b 17 12b 75 Bu,A1 PhMe 1oc 5 12c 85 Bu',Al PhMe 12c 15 14 80 " The reactions were carried out at 0 "C for 10 h.Table 4 Reaction of compound 1 and 2 with DIBAL-H/RM Yield (%) Coumarin RM 11 12 13 14 18 19 13 7 18 85 MeMgI lla 85 13 9 Pr'MgBr lld 49 13 19 a BuLi llc 70 13 2 h 19 90 EtMgBr 12b 90 14 7 PhMgBr 12f 80 'Compound 9d (25%) was isolated. Compound 9c (20%) was isolated. Table 5 Dehydrohalogenation of the isomeric mixture of compound 4 or compound 5 Substrate Method Time (h) Yield (%) of compound 20 Recovery (%) of unchanged substrate 4a a 2 3 20a 92 cisltrans 4b a 2 2 20b 95 cisltrans 4c a 2 5 20c 90 cisitrans 4d a 2 3 20d 95 cisltrans 5b a 2 80 20b 10 trans 5c a 2 92 20c 5 trans 5d a 2 93 20d 5 trans 4a b 2 95 cisitrans 4b b 10 2 20b 90 cisitrans 4c b 10 5 20c 90 cisltrans 5b b 10 2 20b 90 cisltrans 4a C 0.2 33 20a 27 cis137 trans 5b C 3 80 20b 4c C 3 85 20c 5b C 0.2 40 20b 40 cis/10 trans 5b C 3 75 20b 5c C 3 80 20c Method a Boiling benzene with a few drop of pyridine.0.1 mol dm-, NaOAc in Ac,O at room temperature. 0.1 mol dm-, NaOAc in Ac,O at reflux. Starting materials 3-chlorocoumarin,6 3-bromocoumarin ' residue was flash chromatographed on silica gel with methylene and 3-bromo-4-methylcoumarin * were prepared as previously dichloride as eluant, to yield title compound 4a (0.2 g, 60%) as a described.mixture of cisltrans (3/2) isomers; b.p. 4546 "C/O.S mmHg (Found: C, 61.2; H, 4.7. C1,,H9C102 requires C, 61.0; H, 4.6%). Reaction of Compound 1 with Me,CuLi. Synthesis of 3-cis 4a, 6H(200 MHz; CDC13) 1.43 (3 H, d, J 7 Hz), 3.44 (1 H, Chloro-3,4-dihydro-4-methyl-2H-l-benzopyran-2-one4a.-To a dq, J4,7 Hz), 4.71 (1 H, d, J4 Hz) and 6.9-7.4 (4 H, m); m/z 198 stirred suspension of CuI (0.31 g, 1.6 mmol) in dry diethyl ether (Mf + 2,24%), 196 (M+, 78) and 133 (100). (20 cm3) under N2 at -10 "C was added a solution of MeLi in trans-4a 6H(200 MHz; CDCl,) 1.37 (3 H, d, J7 Hz), 3.32 (1 H, diethyl ether (2 cm3; 3.2 mmol).The colourless solution was dq, J 5, 7 Hz), 4.43 (1 H, d, J 5 Hz) and 6.91-7.32 (4 H, m); m/z cooled to -40°C and a solution of compound 1 (0.2 g, 1.1 198 (M+ + 2,24%), 196 (M', 75) and 133 (100). mmol) in diethyl ether (20 cm3) was added dropwise. The mixture was stirred at between -40 and -30 "Cfor 30 min, and Reaction of Compounds 1, 2 and 3 with Organometallic quenched with saturated aq. NH4Cl(15 cm3). The product was Compounds. General Procedure.-(a) With organomagnesium, extracted with EtOAc (3 x 20 cm3) and the extract was washed organolithium, and organomaluminium compounds. To a mag- sequentially with water and brine. The organic layer was dried netically stirred solution of compound 1, 2 or 3 (0.022 mol) in over anhydrous MgS04, the solvent was evaporated off, and the the appropriate solvent (Tables 1-3) (100 cm3) was added J.CHEM. SOC. PERKIN TRANS. 1 1991 Table 6 Chemical shifts and coupling constants (.Pbin Hz) for Ha in compounds 4 and 5 Hb R (X = C1) (X = Br) R Major Minor Major Minor Me 4.71 (4.3) 4.43 (4.6) Et 4.86 (4.6) 4.56 (2.7) 4.80 (3.8) 4.57 (2.2) Bu 4.81 (4.6) 4.52 (2.6) 4.76 (3.8) 4.56 (2.3) Pr' 4.91 (6.3) 4.65 (2.1) 4.87 (5.5) 4.76 (1.9) Table 7 Fractional positional parameters (with esd's) for compound 5d Atom X Y Z 0.589 7(4) 0.032 9(7) 0.125 8(2) 0.377(2) 0.583( 4) 0.19 1(1) 0.602( 2) 0.486(3) 0.186 7(8) 0.490(4) 0.423(6) 0.179( 1) 0.436(3) 0.194(6) 0.155(2) 0.290(3) 0.187(5) 0.106(2) 0.035(3) 0.283(8) 0.132(2) -0.057(3) 0.406(7) 0.153(2) -0.008(3) 0.607( 7) 0.190(2) 0.140(3) 0.653( 7) 0.201(2) 0.231(3) 0.513(7) 0.176(2) 0.186(3) 0.325(6) 0.139(2) 0.302( 3) 0.293(7) 0.040( 1) 0.346(3) 0.527(6) 0.032(2) 0.171(3) 0.192(7) -0.01 l(2) Table 8 Bond lengths (A) and bond angles (") (with esd's) for com- pound 5d 1.912(4) 1.261(5) 1.470(4) 1.423(4) 1.418(3) 1.436(5) 1.099(4) 1.40l(4) 1.490(5) 1.356(5) 1.584(4) 1.368(5) 1.534(4) 1.450(5) 1.534(5) 1.6 14(4) 118.8(3) 117.8(3) 117.8(3) 119.6(4) 114.3(3) 112.9(3) 127.8(4) 123.9(3) 108.5( 2) 123.2(3) 113.0(3) 124.4(3) 117.0(3) 121.1(3) 103.5(3) 114.2(3) 114.0(2) 123.4(3) 110.7(3) 107.5(3) 126.3(4) 118.0(3) 118.8(3) dropwise (30min) the organometallic compound (0.083mol) under nitrogen (see Tables 1-5).At the end of the reaction (monitored by TLC) the solution was poured into ice-water and acidified. The organic layer was decanted, washed with saturated aq.NaHCO,, and dried (MgS04). The mixture (after removal cf the solvent) was chromatographed on silica gel with methylene dichloride (for compounds 4-10) or methylene dichloride-diethyl ether (20: 1) (for compounds 11-14) as eluant, and the products were purified by distillation under reduced pressure or recrystallization from hexane-benzene. (b) Reaction of 3-halogenocoumarin1 or 2 with DZBAL-Hlorganometallic compounds. One-potsynthesis of compounds 11 and 12. To a stirred solution of compound 1 or 2 (2.2 mmol) in toluene (50 cm3) under nitrogen at 40°C was dropped a solution of DIBAL-H in hexane (2.3cm3; 2.3 mmol).The temperature was allowed to rise to 0 "C for 15 min and then a solution of the appropriate Grignard reagent in diethyl ether (4.4mmol) or butyllithium (in hexane) was syringed into the reaction mixture, and the mixture was stirred at 0 "C for 30 min. After hydrolysis, the solution was worked up as described above. The physical and spectral characteristics of the products 4-18,and the optimized experimental conditions and chemical yields are given below. 3-Chloro-4-ethyl-3,4-dihydro-2H-4b.1-benzopyran-2-one [EtMgBr, Et,O; 0°C; 66% as a mixture of cisltrans-isomers (85:15)];b.p. 4647 "(70.2 mmHg (Found C, 62.6;H, 5.2. CllHllC102 requires C, 62.7;H, 5.3%); m/z 212 (M' + 2, 24%), 210 (M', 76)and 181 (100).cis-& 6,(200 MHz; CDCl,) 0.97(3H, t, J7 Hz), 1.63(1H, m), 2.01 (1 H, m), 3.16(1 H, ddd, J 5,9,5 Hz), 4.86(1 H, d, J 5 Hz) and 7.0-7.43 (4 H, m).trans4a 6, 4.56 (1 H, d, J 3 Hz).4-Butyl-3-chloro-3,4-dihydro-2H-l-benzopyran-2-one 4c. [BuMgBr, THF; 0°C; 60% as a mixture of cisltrans isomers (90: lo)];b.p. 100-101"ClO.4 mmHg (Found: C, 65.6;H, 6.15. C13H15C102 requires C, 65.4;H, 6.3%);m/z 240 (M' + 2, 23%), 238 (M', 68)and 181 (100).cis-& 6,(80 MHz; CDCl,) 0.91(3H, t, J6 Hz), 1.40 (4 H, m), 1.69 (1H, m), 1.95 (1H, m), 3.20(1H, ddd, J 5, 8,5 Hz), 4.81 (1 H, d, J 5 Hz) and 7.0-7.4 (4 H, m). trans-& 6,4.52 (1 H, d, J 3 Hz). 3-Chloro-3,4-dihydro-4-isopropyl-2H-1-benzopyran-2-one4d, [Pr'MgBr, Et20-PhMe; 0°C; 61% as a mixture of cisltrans isomers (90: lo)]; b.p. 95-97 "C/0.5 mmHg (Found: C, 64.2;H, 5.7.Cl2H1,C1O2 requires C, 64.15;H, 5.8%);m/z226 (M' + 2, 5%), 224 (M+, 15) and 147 (100).cis-4d m.p. 7&71 OC; 6,(80 MHz; CDCl,) 0.75 (3 H, d, J7 Hz), 1.03 (3 H, d, J 7 Hz), 2.55 (1 H, m), 3.20(1H, dd, J7,4 Hz),4.91 (1 H, d, J6 Hz) and 7.0-7.45 (4H, m). trans-4d6, 4.65 (1 H, d, J 2 Hz). 3-Bromo-4-ethyl-3,4-dihydro-2H-l-benzopyran-2-one5b. [EtMgBr, THF; 0°C; 59% as a mixture of cisltrans isomers (80: 15)](Found: C, 51.7;H, 4.2.C11HllBr02 requires C, 51.8; H, 4.35%);m/z256 (M' + 2, lx),254 (M', 2)and 131 (100). cis-5bm.p. 67-68"C; 6H(200 MHz; CDCl,) 1.00 (3 H, t, J 7Hz), 1.6&2.10(2 H, m), 3.10 (1 H, dt, J4, 7 Hz), 4.80 (1 H, d, J4 H) and 6.70-7.40 (4 H, m).trans-5b 6,4.57 (1 H, d, J 2 Hz). 3-Bromo-4-butyl-3,4-dihydro-2H-l-benzopyran-2-one 5c. [BuMgBr, THF; 0°C; 70% as a mixture of cisltrans isomers (91 :9)] (Found: C, 55.0; H, 5.4.Cl,Hl,Br02 requires C, 55.1;H, 5.3%);m/z284 (M' + 2,2073,282(M', 19)and 107 (100); cis-5c m.p. 75-76 "C;6,(80 MHz; CDCl,) 0.96 (3 H, t, J6 Hz), 1.41 (4H, m), 1.85 (2H, m), 3.13 (1H, dt, J4, 7 Hz), 4.76 (1 H, d, J 4 Hz) and 6.70-7.38 (4 H, m). trans-5c6, 4.56 (1 H, d, J 2 Hz). 3-Bromo-3,4-dihydro-4-isopropyl-2H-1-benzopyran-2-one5d. [Pr'MgBr, Et,O; 0°C;64% as mixture of cisltrans isomers (95:5)](Found: C, 53.4;H, 4.8.C12H13Br02 requires C, 53.55; H, 4.9%);m/z270 (M' + 2,679,268(M', 6)and 147 (100). cis-5b m.p. 57-58 "C; &(80 MHz; CDCl,) 0.84 (3 H, d, J 7Hz), 1.06 (3H, d, J 7Hz), 2.50 (1 H, m), 3.10 (1 H, dd, J 5,6 Hz), 4.87 (1 H, d, J6 Hz) and 6.90-7.30 (4 H, m).trans-% 8, 4.76 (1 H, d, J2 Hz). 3-Chloro-3,4-dihydro-2,4-diphenyZ-2H-l-benzopyran-2-ol6f. (PhMgBr, Et,O-PhMe; 0 "C; 15%); m.p. 187-188 "C (Found: C, 74.8;H, 4.95.C21H17C102 requires C, 74.9;H, 5.1%); 6H[80 MHz; CDCl,-(CD,),SO] 4.3 (1 H, q, J 11 Hz) and 6.65-7.70 (14H, m); m/z338 (M' + 2,2%),336 (M', 4)and 105 (100). Phenyl-2,3-dihydro-3-phenylbenzofuran-2-y1 ketone 7f. (PhMgBr, Et20-PhMe; 0"C; 54%); m.p. 125-126 "C (Found: C, 83.9;H, 5.25.C2,H1602 requires C, 84.0;H, 5.4%);6H[80 MHz; CDCl,-(CD,),SO] 5.02 (1 H, d, J 7Hz), 5.77 (1 H, d, J 7 Hz), 6.80-7.70 (12 H, m) and 7.85-8.10 (2 H, m); m/z 300 (M', 52%) and 167 (100).1,3-diphenylpropan-3-(o-Hydroxyphenyl)-1 -one 8f. (PhMgBr, PhMe; 0"C; 10%); m.p. 167-168 "C (lit.,'71° 166 "C) (Found: C, 83.55;H, 6.1.Calc. for C,,H,,O,: C, 83.4;H, 6.0%); 6,[80 MHz; CDCl,-(CD,),SO] 3.81(1 H, d, J4 Hz), 5.21 (1H, t,J8Hz),6.61-7.38(12H,m),7.71-8.00(2H,m)and8.18(1H, s); m/z302 (M', 2604)and 105 (100). (E)-3-Chloru-4-(o-hydroxyphenyl)-2-methylbut-3-en-2-01 (9a). (MeMgI, Et,O-PhMe; 0"C; 79%); m.p. 105-106 "C (Found:C, 62.2;H, 6.05.C, ,H1 ,ClO, requires C, 62.1;H, 6.2%); 6,@0 MHz; CDC1,) 1.46 (6 H, s), 6.69-7.24 (4 H, m) and 7.04 (1 H, s); m/z 214 (M' + 2,273,212(M+,5) and 179 (100). (E)-2-Chloro-3-ethyl-l-(o-hydroxypheny~pent-l-en-3-ol9b. (EtMgBr, PhMe; 0"C; 63%);m.p. 95-96 "C (Found: C, 64.8;H, 7.2.C13H,,C102 requires C, 64.9;H, 7.1%);6,(80 MHz; CDCl,) 0.94(6H, t, J7 Hz), 1.30-2.11 (4H, m), 6.50-7.23 (4 H, m) and 7.03 (1 H, s); m/z 242 (Mi + 2, 1%), 240 (M', 2) and 165 (100).(E)-3-Butyl-2-chloro-1 -en-3-01 9c,1 -(o-hydroxypheny1)hept-(BuMgBr, PhMe; 0"C; 80%); m.p. 84-85 "C (Found: C, 68.8; H, 8.4.C1,H2,C102 requires C, 68.8;H, 8.5%); 6,(80 MHz; CDCl,) 0.92 (6 H, m), 1.1Cb2.11 (12H, m), 6.87(1 H, s) and 6.90-7.26 (4 H, s); m/z298 (M' + 2, 1%), 296 (Mi, 3)and 221 (100). (E)-2-Chloro-1-(o-hydroxyphenyl)-3-isopropyl-4-methylpent-1-en-3-019d. (Pr'MgBr, Et,O; 0"C; 36%); m.p. 122-123 "C H, 7.7.(Found: C,67.1; C15H21C102requires C, 67.0;H, 7.9%); hH(8O MHz; CDCl,) 0.71-1.62(6 H, m), 1.82-2.51 (2 H, m), +6.71-7.47 (4 H, m) and 6.79 (1 H, s); mjz 270 (M + 2, l%), 268 (M+,4)and 71 (100).J. CHEM. SOC. PERKIN TRANS. 1 1991 CDCl,) 6.52-7.53 (14 H, m) and 7.02 (1 H, s); m/z 364 (M' + 2 -H20,273,362 (Mi -H,O, 2)and 283 (100). (E)-3-Chloro-4-(o-hydroxyphenyZ)but-3-en-2-ollla.(DIBAL-H/MeMgI, PhMe; 0 "C; 79%);m.p. 127.5-128.5"C (Found: C, 60.4;H, 5.5. C,,H, ,C102 requires C, 60.5;H, 5.6%);6,(80 MHz; CDCl,) 1.38 (3 H, d, J6 Hz), 4.71 (1 H, q, J6 Hz), 6.68(1H, s) and 6.71-7.23 (4 H, m); m/z 200 (M+ + 2,1%),198 (Mf, 4)and 165 (100). (E)-2-Chloro-l-(o-hydroxyphenyl)pent-l-en-3-ulllb. (Et,Al, PhMe; 0 "C; 50%); m.p. 74-75"C (Found: C, 62.15;H, 6.1. C,1H,,C102 requires C, 62.1;H, 6.2%);6,(80 MHz; CDCl,) 0.9 (3H, t, J7 Hz), 1.75 (2 H, qd, J7,7 Hz),4.34 (1 H, t, J7 Hz), 6.93 (1H, s) and 6.98-7.31(4H, m); m/z 214 (M+ + 2,1%),212 (Mi, 4)and 165 (100). (E)-2-Chloro-l-(o-hydruxyphenyl)hept-l-en-3-ol1lc.(Bu,Al, PhMe; 0°C; 78%); m.p. 78-79°C (Found: C, 64.8;H, 7.2. C13H1,C102 requires C, 64.9;H, 7.1%);6,(80 MHz; CDCl,) 0.8 (3H, t, J 5 Hz), 1.22 (4H, m), 1.69(2H, m), 4.57 (1 H, t, J7 Hz), 6.71(1 H, s) and 6.81-7.22 (4 H, m); m/z242 (Mi + 2, 1%), 240 (M+,2)and 165 (100). (E)-2-Chloro-1-en-3-o/1-(o-hydroxyphenyl)-4-methylpent-lld. (Pr'MgBr, PhMe; 0"C; 49%);m.p. 100-101 "C (Found: C, 63.6;H, 6.5.C12H1,C102 requires C, 63.6;H, 6.7%);6,(80 MHz; CDCl,) 0.81 (3 H, d, J7 Hz), 1.01 (3 H, d, J7 Hz), 1.7Cb2.11(1H, m), 3.99(1H, d, J9 Hz), 6.75 (1 H, s) and 6.81-7.28(4H, m); m/z 228 (M' + 2,1%),226 (M', 4)and 165 (100). (E)-2-Chloro-1 -en-3-ol1 -(o-hydroxyphenyl)-5-methylhex-lle.(Bu,'Al, PhMe; 0"C; 34%);m.p.84-85 "C (Found: C, 65.0; H, 7.2.Cl3H1,C1O2 C, 64.9;H, 7.1%);6,(80 MHz; CDCl,) 0.74 (3H, d, J 6 Hz), 0.85 (3 H, d, J 6 Hz), 1.12-1.20 (1 H, m), 1.51-1.62 (2H, m), 3.5 (1H, m), 6.75 (1 H, s) and 6.81-7.22 (4 H, m); mjz 242 (Mi + 2, 1%), 240 (M', 2),and 165 (100). (E)-2-Brorno-1 -(o-hydroxyphenyl)pent-l-en-3-ol 12b. (DIBAL-H/EtMgBr, PhMe; 0"C; 79%); m.p. 94-95 "C (Found: C, 51.3; H, 5.15. C,,H,,BrO, requires C, 51.4;H, 5.1%);FH(80MHz; CDC1,) 0.84(3 H, t, J 7 Hz), 1.79 (2 H, q, J7 Hz), 4.24(1 H, t, J7 Hz), 6.71-7.31 (4 H, m) and 7.01(1 H, s); (E)-2-Chloro-3-(o-hydroxyphen~~l)-l,l-diphenylprop-2-en-l-olm/z258 (Mi +2,9%),256 (M', 9)and 209 (100).9f.(PhMgBr, PhMe; 0"C; 54%); m.p. 146-147 "C (Found: C, (E)-2-Bromo-hydroxypheny 1)hep t-1-en-3-01 12c. (Bu,Al,1 -(0-74.6; H, 5.1%);6,[80 MHz; PhMe; 0°C; 78%); m.p. 79-80°C (Found: C, 54.9;H, 5.9.H, 5.2.C2 ,H, ,C102 requires C, 74.9; CDC1,-(CD3),S0] 6.75 (1 H, s) and 6.89-7.72 (14 H, m); m/z C,,H,,BrO, requires C, 54.75;H, 6.0%);6,(80 MHz; CDC1,) 338 (M' + 2,279,336(M', 2)and 105 (100). 0.87 (3 H, t, J 5 Hz), 1.12-1.51 (4H, m), 1.57-1.73 (2 H, m), 4.38 (E)-3-Bromo-4-(o-hydroxyphenyl)-2-methylb~?-3-en-2-0110a.(1H, t, J 6 Hz), 6.7 1-7.29 (4 H, m) and 7.01 (1 H, s);m/z286 (M + + 2,23%), 284 (M', 24)and 209 (100). (MeMgI, PhMe; 0 "C; 70%);m.p. 89-99 "C (Found: C, 51.5;H, 5.15. CI1Hl3BrO2 requires C, 51.4;H, 5.1%); 6,(80 MHz; CDCl,) 1.47 (6 H, s), 6.747.25 (4 H, m) and 6.91(1H, s); m/z 258 (Mf + 2,273,256(M+, 2)and 115 (100).(E)-2-Bromo-3-ethyl-1 -en-3-01lob.1-(0-hydroxypheny1)pent-(EtMgBr, PhMe; 0"C; 60%);m.p. 100-101"C (Found: C, 54.9; H, 5.7.C,,H,,BrO, requires C, 54.75;H, 6.0%);6,(80 MHz; CDCl,) 0.95 (6 H, t, J7 Hz), 1.11-2.10 (4 H, m), 6.72-7.25 (4 H, m) and 7.06 (1 H, s); m/z 286 (M+ + 2,14%), 284 (M', 15)and 128 (100). (E)-2-Bromo-3-butyl-1-en-3-ol1Oc.1-(o-hydroxypheny1)hept-(BuMgBr, PhMe; 0"C; 63%); m.p. 87.5-88.5"C (Found: C, 59.65;H, 7.3.C17H,,Br02 requires C, 59.8;H, 7.4%);6,(80 MHz; CDC1,) 1.05 (6 H, m), 1.15-2.09(8 H, m), 2.51-2.71 (4 H, m), 6.71-7.25 (4 H, m) and 7.05 (1 H, s); mjz 342 (M+ + 2, 1%), 340 (Mf, 1)and 85 (100).(E)-2-Bromo-1-(o-hydroxyphenyl)-3-isopropyl-4-methylprop-1-en-3-0110d.(Pr'MgBr, PhMe; 0"C; 20%); m.p. 119-120 "C (Found: C, 57.45;H, 6.7.C15H,,Br0, requires C, 57.5;H, 6.8%);6,(80 MHz; CDC1,) 0.81-1.85 (12 H, m), 1.71-2.72 (2 H, m), 6.70-7.49 (4 H, m) and 7.01 (1 H, s); m/z314 (M+ + 2, l%), 312 (M+, 1)and 91 (100). 2-Brorno-3-(o-hydroxyphenyl)-1-011Of.1,l-diphenylprop-2-en-(PhMgBr, PhMe; 0"C; 14%);m.p. 121-122 "C (Found: C, 66.3; H, 4.55.C,,H1,BrO2 requires C, 66.2;H, 4.5%);6,(80 MHz; (E)-2-Bromo-1 -en-3-01l-(o-hydroxyphenyl)-4-methylpent-12d.(Pr'MgBr, PhMe; 0"C; 50%); m.p. 122-123 "C (Found: C, 55.1; H, 5.5. C12HlSBr02 requires C, 53.15; H, 5.6%);6,(80 MHz; CDCl,) 0.77 (3 H, d, J7 Hz), 1.01 (3 H, d, J7 Hz), 3.77 (1 H, d, J 9 Hz), 6.91-7.13 (4H, m) and 7.03 (1 H, s); m/z 272 (M ' + 2,673270(M', 7)and 211 (100).(E)-2-Bromo-3-(o-hydroxyphenyl)-1-011 -phenylprop-2-en-12f.(DIBAL-H/PhMgBr, PhMe; 0"C; 7%); m.p. lO(r101"C (Found: C, 59.2; H, 4.2.C1,H,,Br02 requires C, 59.0;H, 4.3%);6,(80 MHz; CDC1,) 5.61 (1H, s), 7.02 (1 H, s) and 6.73-7.41 (9 H, m); m/z306 (M' + 2, l%), 304 (M+, 1)and 207 (100). (E)-2-Chloro-3-(o-hydroxyphenyl)prop-2-en-l-ol13.(Bu',AI, PhMe; 0"C; 43%); m.p. 109-1 10 "C (Found: C, 58.4;H, 4.8. C9H,C10, requires C, 58.55; H, 4.9%);6,(80 MHz; CDC1,) 4.20 (2H, s), 6.6(1 H, s), 6.71-7.15 (4 H, m) and 7.02 (1 H, s); m/z186 (M+ + 2,479,184(M+, 14)and 131 (100). 2-Bromo-3-(o-hydroxyphenyl)prop-2-en-l-ol14. (Bu',Al, PhMe; 0°C; 72%); m.p.129-130°C (Found: C, 47.3;H, 3.9. C,H,BrO, requires C, 47.2;H, 4.0%);6,[80 MHz; CDC1,- (CD,),SO] 4.18 (2 H, s), 6.96(1H, s) and 6.75-7.25(4 H, m); m/z230 (M+ + 2,473,228(Mf, 4)and 131 (100). (Z)-4-(o-Hydroxyphenyl)-2-methylbut-3-en-2-ol15a. (2, MeLi, Et,O; 0"C; 23%); m.p. 53 "C (lit.," 53-55 "C); 6,(80 J. CHEM. SOC. PERKIN TRANS. 1 1991 MHz; CDC1,) 1.33 (6 H, s), 5.93 (1 H, d, J 12 Hz), 6.36 (1 H, d, J 12 Hz) and 6.71-7.21 (4 H, m). (Z)-3-Butyl-1-(0-hydroxypheny1)hept-1-en-3-011%. (2, BuLi, PhMe; -40 "C; 32%);yellow oil; 6,(80 MHz; CDC1,) 0.86 (6 H, m), 0.93-1.71 (12 H, m), 5.71 (1 H, d, J 13 Hz), 6.36 (1 H, d, J 13 Hz) and 6.71-7.21 (4 H, m); m/z 263 (M+ + 1, 679,262 (M', 30) and 205 (100); On distillation this compound was transformed into 2,2-dibutyl-2H- 1-benzopyran.Yellow oil, b.p. 96 "Cjl mmHg (lit.," 161-163 "C/15 mmHg); 6,(80 MHz; CDCl,) 0.87 (6 H, m), 0.94-1.80 (12 H, m), 5.44 (1 H, d, J 10 Hz), 6.34 (1 H, d, J 10 Hz) and 6.71-7.20 (4 H, m); m/z 245 (M+ + 1, l%), 244 (M+,4) and 187 (100). (E)-4-Bromo-3-ethyl-5-(o-hydroxyphenyl)hex-4-en-3-ol16b. (EtMgBr, Et20; 0 "C; 65%); m.p. 84-85 "C (Found: C, 56.15;H, 6.3. C14H19Br02 requires C, 56.2; H, 6.4%); 6,(80 MHz; CDC13)0.89 (3 H, t, J7 Hz), 0.95 (3 H, t, J7 Hz), 1.61 (2 H, m), 2.01 (2 H, m), 2.19 (3 H, s), 6.71-7.17 (4 H, m) and 6.91 (1 H, s); mjz 300 (M+ + 2,773,298 (M+,8) and 57 (100). 3-Chloro-2H-1-benzopyran-2-01 18. (DIBAL-H. PhMe; -40 "C; 79%); m.p. 162-163 "C (Found: C, 59.4; H, 3.8.C9H,C10, requires C, 59.2; H, 3.9%); 6J80 MHz; CDCI,-(CD,),SO] 6.06 (1 H, s), 6.75 (1 H, s) and 6.82-7.21 (4 H, m); m/z 184 (M+ + 2, 1%), 182 (M+, and M+ + 2 -H2, 34) and 180 (M+ + H,, 100). 3-Bromo-2H- 1-benzopyran-2-01 19. (DIBAL-H, PhMe; -40°C; SOo(,); m.p. 155-156 "C (Found: C, 47.7; H, 3.2. C,H,BrO, requires C, 47.6; H, 3.1%); 6H[80 MHz; CDCl,- (CD,),SO] 5.78 (1 H, s), 6.82 (1 H, s) and 6.78-7.31 (4 H, m); m/z 228 (M' + 2,17%), 226 (M', 17) and 147 (100). Dehydrohalogenation of Compounds 4 and 5. Synthesis of 4-Alkylcoumarins20.-A mixture cis-and trans-4 or 5 (1.6 mmol) in the appropriate solvent (20 cm3) was refluxed with a base (Table 5) until the reaction was complete (TLC). The solution was cooled to room temperature and acidified with 6 mol dm-, HCl. The organic layer was decanted, washed with aq.NaHC0, and dried over anhydrous MgS04. The solvent was eliminated and the residue was recrystallized from chloroform. The following compounds were thus prepared. 4-Methyl-2H-1 -benzopyran-2-one 20a. (Ac, 0-NaO Ac; 52%); m.p. 81-82°C (lit.,', 82°C) (Found: C, 74.8; H, 4.9. Calc. for ClOHBO2:C, 75.0; H, 5.0%); FH(80MHz; CDC1,) 2.51 (3 H, d, J 1 Hz),6.18(1 H,q, JlHz)and6.85-7.61(4H,m). 4-Ethy1-2H-l-benzopyran-2-one20b. (C6H,-pyridine, 5b; 75%);m.p. 69-70 "C (lit.,', 70 "C) (Found: C, 75.9; H, 5.7. Calc. for CllH1002: C, 75.85; H, 5.9%); tiH(8O MHz; CDCl,) 1.36 (3 H, t, J 7 Hz), 2.81 (2 H, m), 6.29 (1 H, t, J 1 Hz) and 7.09-7.84 (4 H, m); m/z 174 (M+,40% and 131 (100) 4-Butyl-2H- 1-benzopyran-2-one 2Oc.(C,H,-pyridine 5c; 89%); m.p. 67-68OC (Found: C, 77.1; H, 6.85. C13H1402 requires C, 77.2; H, 7.0%); 6,(80 MHz; CDCl,) 0.99 (3 H, td, J6, 1 Hz), 1.09-1.98 (4 H, m), 2.77 (2 H, m), 6.26 (1 H, t, J 1 Hz) and 7.12-7.61 (4 H, m); m/z 203 (M+ + 1, 473, 202 (M ', 20), and 160 (100). 4- Isopropyl-2H- 1-benzopyran-2-one 20d. (C,H,-pyridine, 5d, 8404); b.p. 85-86 "C/1 mmHg (Found: C, 76.7; H, 6.35. C12H1202requires C, 76.6; H, 6.4%); 6,(80 MHz; CDCl,) 1.31 (6H,d,J7Hz),3.30(1H,m),6.27(1H,d,JlHz)and7.05-7.61 (4 H, m); m/z 189 (M+ + 1,773,188 (M+, 51) and 145 (100). X-Ray Crystallographic Structure Determination of Com-pound 5d.--Crystal data. The structure of compound 5d, * The fractional atomic co-ordinates, bond lengths and angles, torsion angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (see 'Instructions for Authors,' J.Chem. Soc., Perkin Trans. I, 1991, issue 1, p. xviii). C12H1,Br02, was determined by X-ray diffraction. M, = 269.14, monoclinic, space group P21/c, a = 9.411(2), b = 5.843(6), c = 21.100(5) A, p = 99.47(2)", V = 1 144(1) A3, 2 = 4, D, = 1.56 g ern-,. Mo-Ka radiation (graphite crystal monochromator, h = 0.71073 A, p(Mo-Ka) = 35.3 cm-', F(OO0) = 544, T = 293 K. Final conventional R-factor = 0.154 for 954 'observed' reflections and 125 variables. Colourless crystal, 0.33 x 0.23 x 0.17 mm. Mo-Ka radiation with graphite crystal monochromator, Enraf-Nonius CAD4 single-crystal diffractometer.Unit-cell dimensions were deter- mined from the angular settings of 25 reflections with 10" 8 15". Space group was determined to be P21/c from systematic absences. 3694 Reflections measured, hkl range (-13,0,0)to (13,8,29), theta limits (0" 8 30"). e28 Scan technique with a variable scan rate with a maximum scan time of 30 s per reflection. Intensity checked by monitoring three standard reflections every 60 min. Crystals were very unstable under X-rays and led to very high drift corrections. Because of this, neither good values of agreement factors nor accurate parameters were expected. Nevertheless, data collection and structure determination were carried out since the main interest of the work was to determine the molecular geometry.Final drift correction factors were between 1.00 and 2.29. Profile analysis was performed on all reflection^.'^.'^ Some doubly measured reflections were averaged, Rint= C(I -(I))/CI = 0.095, 1009 unique reflections and 954 observed with I 30(I). Lorentz and polarization corrections were applied and data reduced to IF]-values. Structure solved by direct methods, using the program SHELX86.l6 Isotropic least-squares refine- ment, using SHELX,17 converged to R = 0.20. Anisotropic refinements followed by a difference Fourier synthesis allowed the location of some hydrogen atoms. Positional parameters and anisotropic thermal parameters of the non-hydrogen atoms were refined, except those for O(2 l), C(4) and C(42) which were isotropically refined.All the hydrogen atoms were isotropically refined, with a common thermal parameters, riding, at constraining distances, on their parent atoms, except for H(31) and H(41), which co-ordinates were fixed. The final conventional agreement factor was R = 0.154 for the 954 'observed' reflections and 125 variables. Function minimized Zw(Fo -F0),, w = 1. Maximum shift- over-error ratio in the last full-matrix least-squares cycle was 0.001. Final difference Fourier map showed no peaks 1.32 e A-3 nor -2.56 e A-3. Fractional positional parameters for non-hydrogen atoms are given in Table 7, while Table 8 collects selected geometrical parameters.* Atomic scattering factors were taken from the International Tables for X-ray Crystal- lography.'* The plot was made with the PLUTO l9 program.Geometrical calculations were made with PARST.,' All cal- culations were made on an IBM 3090 Computer at the Computer Center of the University of Oviedo. References 1 Chr. Ivanov and A. Bojilova, Synthesis, 1974,708. 2 G. A. Holmberg, Acta Chem. Scand., 1961,15,1255. 3 I. Renvall, Acta Acad. Aboensis, Math. Phys., 1969, 29, 1 (Chem. Abstr., 1970,72,66737~). 4 A. Alberola, F. Alonso and A. Gonzalez Ortega, Ah. Quin., Ser. C, 1982,78,9. 5 A. Alberola, A. Gonzalez, R. Pedrosa, J. L. Perez and J. F. Rodriguez, J. Heterocycl. Chem., 1983,20, 715. 6 J. C. Heeth, S. Z. Cardon and H. S. Halbedel, USP 2 466 657/1949 (Chem. Abstr., 1949,43, 7513f). 7 K. A. Thakar, J. Indian Chem. SOC., 1963,40,539. 8 J. Lecocq, Ann. Chim., 1948,3,62. 9 A. Lowenbein, E. Pongracz and E. A. Spiess, Ber. Dtsch. Chem. Ges., Abt. B, 1924,57,1517. 10 G. A. Holmberg and J. Axberg, Acta Chem. Scand., 1963,17,967. 210 11 L. I. Smith, P. M. Ruoff and W. B. Irwin, J. Am. Chem. SOC.,1940,62, 12. 12 E. H. Woodrukk, Org. Synth., 1944,24,69. 13 W. Cocker, B. E. Cross, J. T. Edward, D. s. Jenkinson and J. Mc. Cormick, J. Chem. Soc., 1953,2355. 14 M. S. Lehman and F. K. Larsen, Acta Crystallogr., Sect. A, 1974,30, 580. 15 D. F. Grant and E. J. Gabe, J. Appl. Crystallogr., 1978, 11, 114. 16 G. M. Sheldrick, SHELX86, Crystallographic Computing 3,eds. G. M. Sheldrick, C. Kruger and R. Goddard, Clarendon Press, Oxford, 1985, p. 175. 17 G. M. Sheldrick, SHELX, A Program for Crystal Structure Determination, University Chemical Laboratory, Cambridge, England, 1976. J. CHEM. SOC. PERKIN TRANS. 1 1991 18 International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4. 19 W. D. S. Motherwell, PLUTO, A Program for Plotting Molecular and Crystal Structures, University Chemical Laboratory, Cam- bridge, England, 1976. 20 M. Nardelli, Comput. Chem., 1983,7, 95. Paper 0/02837A Received 25th June 1990 Accepted 2nd August 1990