J.C.S. Perkin IThe Lithium Enolate of Cyclo-octa-2,4,6-trienone and its Reactions withElect roph ilesBy Penelope A. Chaloner and Andrew B. Holmes," University Chemical Laboratory, Lensfieid Road, CambridgeLithium di-isopropylamide catalysed rearrangement of 7.8-epoxycyclo-octa-1.3.5-triene at low temperature givesthe lithium enolate of cyclo-octa-2,4,6-trienone, which can be alkylated at C-8 with reactive electrophiles such asmethyl iodide, allyl bromide, ethyl iodide, benzyl iodide, and benzeneselenenyl bromide. Bromination of theenolate also occurs at C-8, but reagents such as acetyl chloride and ethyl chloroformate yield only the products ofO-acylation.CB2 1 EWIN 1951 Cope and Tiffany reported the first preparationof cyclo-octatrienone (3) by a lithium diethylamidecatalysed rearrangement of epoxycyclo-octatriene (1).Further investigation of the properties of cyclo-octatrienone (3) revealed that it formed normal deriv-atives of the carbonyl group, but that it was extremelyresistant to reactions involving the enolate anion (2).For example, although the trienone (3) was soluble inaqueous sodium hydroxide, it resisted all attempts toform alkyl derivatives by treatment with alkyl halides inthe presence of alkoxides.Subsequent studies by Mat-suda and his co-workers revealed that, under forcingconditions, nucleophilic alkoxides attack the carbonylgroup of cyclo-octatrienone and induce a ring contractionto cyclohexa-2,5-dienylacet at e esters. Nevertheless,Roberts has reported deuteriation experiments withcyclo-octatrienone, presumably involving the enolate (2).Five deuterium atoms were incorporated, at positions 2,4,6, and 8, by equilibrating cyclo-octatrienone with NaODin D,O under extremely forcing conditions. Using non-nucleophilic bases and various electrophiles, Gund andCarpino 5 were unable to convert cyclo-octatrienoneinto any substituted derivatives, and these resultstherefore suggest that the enolate anion (2) cannot begenerated by abstracting a proton from (3).Cope and Tiffany had suggested that the formationof cyclo-octatrienone (3) from epoxycyclo-octatriene (1)involved abstraction of a proton at C-1 and rearrange-ment to the enolate anion (a), followed by protonation togive (3) during the subsequent work-up.We thereforeconcluded that the most reasonable method of generatingthe enolate anion (2) was by base-catalysed rearrange-ment of (1) at low temperatures. Capture of the enolateanion (2) by an electrophile could result in C- or O-alkylation. If C-alkylation were a major pathway thisreaction could provide a convenient synthetic route toa wide variety of substituted cyclo-octatrienones, includ-A. C. Cope and B. D. Tiffany, J . Amer. Chem. SOC., 1951, 73,A. C. Cope, S. F. Schaeren, and E. R. Trumbull, J . Amer.M. Ogawa, M. Takagi, and 3.. Matsuda, Chem. Letters, 1972,4158.Chem. SOC., 1954, 76, 1096.627.ing a suitable precursor to cyclo-octatriene-l,2-dione.The only other method available for the preparation ofcyclo-octatrienone derivatives is the rather limited andlow-yielding diazoalkane-induced ring expansion oftropone.6In order to test the feasibility of generating andtrapping the enolate anion (2) by this method, epoxy-cyclo-octatriene (1) was added to a solution containinga slight excess of lithium di-isopropylamide in tetra-hydrofuran a t -78 "C.The mixture was allowed towarm to 0 O C , and then quenched with a large excess ofacetic 2Hacid. After work-up and distillation, thedeuteriated cyclo-octatrienone isolated (76) was shownby n.m.r. and mass spectrometry to have incorporatedone deuterium atom at C-8 to the extent of 85. En-couraged by this result, we investigated the reactions ofcarbon electrophiles. Addition of a large excess ofmethyl iodide to the solution of the enolate anion (2) intetrahydrofuran, followed by stirring at room temper-ature (4 h) and work-up, afforded a very small amount ofalkylated product (4), the major product being cyclo-octatrienone (3) itself.The lithium enolate anion (2)generated in this way may have been too unreactivetowards alkylation and had simply been protonatedduring the aqueous work-up. In such a situationhexamethylphosphoric triamide (HMPA) could beexpected to activate the lithium enolate anion (2) toattack by carbon electrophiles. The use of a largeexcess of HMPA as a co-solvent in the above reactionmixture afforded a deep red solution of the enolateanion (2) which could be alkylated with an excess ofmethyl iodide to give 8-methylcyclo-octatrienone (4;R = Me) in 78 yield.Therefore, in all subsequentwork reported here, including deuteriation experiments,HMPA was used as co-solvent.The results of the reactions of the enolate (2) withvarious electrophiles are summarised in Table 1.Table 1 shows that reactive electrophiles (methyliodide, ethyl iodide, and allyl bromide) will alkylate theenolate anion (2) in the position, whereas O-alkylationis not observed. However, when the only slightly lessreactive ethyl bromide is used as alkylating agent, someO-alkylation (1 1) occurs. The only reactive electro-phile which gave surprisingly low amounts of C-alkylatedproduct (15) was benzyl bromide. In this case,* C. Ganter, S. M. Pokras, and J. D. Roberts, J . Amer. Chem.SOL, 1966, 88, 4235.P.H. Gund, Ph.D. Dissertation, University of Massachusetts,1967.M. Franck-Neumann, Tetvahedrotz Letters, 1970, 21431976 1839however, O-alkylation did not seem to be a competingreaction. Rather, the enolate or an alkylation productLiNPri2HMPA-THFRX 4( 5 1seemed to polymerise at a rate comparable to that forC-alkylation, and on work-up at a stage when poly-merisation seemed to have been significant, the mainbromination of enolates.9 Thus, direct bromination ofthe enolate (2) afforded the bromo-ketone (4; R = Br)as an unstable low-melting solid. Methods for trans-forming this compound into the a-diketone (6) are underinvestigation.(6 1 (41 (7)In connection with approaches to functionalisation ofthe enolate (2) at C-8, its reactions with various sulphurand selenium electrophiles were studied.Addition ofdiphenyl disulphide or benzeneselenenyl chloride lo tothe enolate at -78 "C resulted in varying quantities ofthe acetophenone derivatives (9; R = SPh) and (10;R = SPh) and (9; R = SePh) and (10; R = SePh),TABLE 1Reactions of the enolate (2) with electrophilesYield ofcyclo-octatrienoneYield of (4; R = H) Yield of14Elec trophile Time (h) Temp. ("C) R ( 4 ) g J ) () (5) (96)SleC0,D 0.08 0 DMe I 2.0 -78 to 20 Me 78CH,:CHCH,Br 4.0 -78 to 20 CH,:CH-CH, 74EtBr 12.0 -78tO -5 Et 16 22 11EtI 12.0 -78 to -5 Et 81PhCH,Br 3.0 -78 to -5 PhCH, 15 48PhCH,I 3.0 -78 to -5 PhCH, 37 51MeCOCI * 2.0 -7s to -5 amp;4C 36 9CIC0,Et * 2.0 -78 to -5 Et0,C 62 28PliSeBr 7 0.5 -78 to 20 PhSe 40PIlSCI t 0.5 -78 to 20 PhS 26Rr, 0.08 - 78 Br 51* Two-fold excess of enolate used. 7 Inverse addition of enolate at - 78 "C to electrophile at - 78 "C.characterisable by-product was cyclo-octatrienone (4;R = H) itself.The use of benzyl iodide improved theyield of (4; R = PhCH,), but polymerisation was stillobserved to be a competing side reaction.Attempted C-acylation to give a p-diketone or a p-keto-ester was completely unsuccessful. It is knownthat effective C-acylation of simple enolates dependsupon adding the acylating agent to a two- or three-foldexcess of the enolate.' Even under these conditions thereaction of the enolate (2) with acetyl chloride affordedthe product of O-acylation (5; R = Ac) (9yo), and withethyl chloroforniate ( 5 ; R = C0,Et) (28).Withequimolar quantities of acylating agent, O-acylationoccurred to a greater extent (26 and 63, respectively).Our investigation of the reactions of the enolate anion(2) was in part stimulated by our interest in the cyclo-octatrienediones.8 Functionalisation of the enolate (2)at C-8 could be expected to provide a convenient pre-cursor of cyclo-octatriene-l,2-dione (6). a-Functional-isation of ketones has recently been achieved by directH. 0. House, ' Modern Synthetic Reactions,' Benjamin,P. A. Chaloner, A. B. Holmes, M. A. McKervey, and R. A.P. L. Stotter and K. A. Hill, J . Org. Chem., 1973, 38, 2576.California, 1972, pp. 762-765.Raphael, Tetrahedron Lcttevs, 1975, 265.respectively.The formation of these products caneasily be rationalised by a reaction of the bicyclic valencetautomer (7). In the unsubstituted cyclo-octatrienone(4; R = H), the bicyclic form is known to be in equili-brium with the monocyclic form to the extent of about5 at 20 OC.l*ll Deprotonation of the bicyclic species(7) at the ring junction by residual base or enolate (2)could lead to a species which should form a stable enolate(8) by an aromatisation process and cleavage of the four-membered ring. Protonation of the enolate (8) wouldyield (9), whereas further reaction with an electrophileRX would give (10). Similar reactions have beenobserved by G ~ n d . ~ This problem can be avoided byusing a very reactive electrophile whose leaving group isa poor base, and by ensuring that no residual base ispresent to deprotonate the bicyclic valence tautomer (7).Thus, addition of a cooled (-78 "C) solution of the eno-late (2) to benzeneselenenyl chloride or bromide a t-78 "C gives satisfactory yields of the S-phenylseleno-cyclo-octatrienone (4; R = SePh), whereas use oflo H.J. Reich, J. M. Renga, and I. L. Reich, J . A w w . Chem.SOL, 1975, 97, 5434.l1 R. Huisgen, F. Mietzsch, G. Boche, and H. Seidl, Chem. SOC.Special Publ. No. 19, 1965, pp. 3-20; M. Brookhart, G. 0.Nelson, G. Scholes, and R. A. Watson, J . C . S . Chem. Comm., 1976,195J.C.S. Perkin Ibenzenesulphenyl chloride results in poorer yields of thephenylthio-compound (4 ; R = SPh) .0-The physical properties of the alkylcyclo-octatrienones(4) are similar to those of cyclo-octatrienone itself.Theyall possess a characteristic smell, are all yellow oilstetrahydrofuran (THF) (20 ml) and hexamethylphosphorictriamide (HMPA) (3 ml, 17 mmol) was prepared by adding asolution of n-butyl-lithium (Aldrich; ca. 17 solution inhexane; 3.3 mmol estimated by titration 12) to di-isopropyl-amine (0.426 ml, 3 mmol) in the THF-HMPA solvent at-78 "C. The mixture was stirred under argon for 10 minat -73 "C, and a solution of eposycyclo-octatriene 1 (1)(360 mg, 3 mmol) in THF (2 nil) was then added by syringethrough a septum cap. A deep red colour was generatedimmediately, and the solution was used after having beenstirred for 10 niin at - 78 "C. The solution was indefinitelystable at temperatures -30 "C, but above this teniper-ature i t slowly polynierised.The enolate anion (2) (3 mmol)in THF-HMPA (23 ml) was prepared as described abovefor all the following experiments (this description is notrepeated).8-2HlCycZo-octatrienone (4; R = D) .-A solution ofthe enolate (2) (3 mmol) was quenched with an excess ofacetic Wlacid (prepared from Ac20 and D20) at 0 "C.After being stirred for 5 inin a t 0 O C , the mixture waswarmed to room temperature and diluted with water.TABLE 2U.V. and visible spectra of cyclo-octatrienones (4) in cyclohesaner 7Amax./nm (4 R -AH a 245 (7 000) 282 (4 300) 360 (500)Me 216 (8 800) 245 (4 900) 281 (4000) 359 (400)Et 216 (12 800) 247 (4 500) 381 (3 300) 360 (400)282 (3 600) 361 (400) CH2:CHCH, 215 (9 SOO)PhCH, 220 (11 400) 248 (5 700) 284 (3 500) 361 (400)246 (5 900)a Ref.1. Ref. 6.boiling at moderate temperatures, and are sensitive toair, moisture, and protic solvents. The i.r. spectrareveal that the bicyclic tautomer (7) is present to agreater extent than in cyclo-octatrienone itself (a two-fold enhancement in the intensity ratio of the band at1 780 cm-l relative to the band at 1 660 cm-l is observed).and this trend is evident in the disubstituted cyclo-octatrienone studied by Franck-Neumann,6 where thebicyclic form predominates almost completely.The U.V. spectra of the alkyl cyclo-octatrienones (4)resemble that of cyclo-octatrienone itself (see Table 2) anda further similarity to theunsubstituted compoundis theirresistance to further alkylation via their enolate anions.EXPERIMENTALM.p.s were determined with a Kofler hot-stage apparatus.lH N.m.r. spectra were recorded a t 100 MHz with a VarianHA- 100 spectrometer, and Fourier transform proton noisedecoupled I3C n.m.r.spectra were determined at 20 MHzwith a Varian CFT-20 spectrometer, both with tetramethyl-silane as standard. 1.r. spectra were recorded for 2.5(wlv) solutions with a Perkin-Elmer 257 spectrometer, andelectronic spectra for solutions in cyclohexane or ethanolwith a Unicam SP 1800 spectrometer. Mass spectra wererecorded with an A.E.I. MS30 instrument. Microanalyseswere determined by 1Mr. D. Flory and his staff a t the Univer-sity Chemical Laboratory.Preparative layer chromato-graphy was carried out on 20 x 20 cm glass plates coatedto a thickness of 1 mm with Merck Kieselgel PF,,,.Preparation of the EizoZate Aniofz (2) of Cyc2o-octatrienone(3) .-A solution of lithium di-isopropylaniide (3 mmol) inThe resulting solution was extracted with hexane, and theindividual hexane extracts were washed sequentially withsaturated aqueous sodium hydrogen carbonate and satur-ated aqueous sodium chloride. The combined organiclayers were dried (Na,SO,) and concentrated to a yellow oilwhich was distilled (Kugelrohr; oven temp. 85-88 "C;12 mmHg) to give 8-2Hlcyclo-octatrienone (4; R = D)(321 ing, 89). Comparison of the 1H n.m.r. spectrum ofthis compound with the reported spectrum of cyclo-octatrienone (4; R = H) showed that one deuterium atomhad been incorporated at C-8.The ratio of the intensitiesof the (M + 1)+ and M+ Feaks in the high resolution massspectrum showed that the isotopic purity of the deuteriatedcyclo-octatrienone (4; R = D) was ca. 85.8-MethyZcycZo-octa-2,4,6-trienone (4; R = Me) .G-Methyliodide (2 ml, 32 mmol) (purified by filtration through basicalumina, activity 1, immediately before use) was added to astirred solution of the enolate (2) (3 mmol) at -78 "C. Themixture was allowed to warm to room temperature over1.5 h, during which time the colour faded to a pale yellow.After a further 0.5 h the mixture was diluted with water andextracted with hexane. The extracts were washed sequen-tially with water and saturated aqueous sodium chloride,then combined and dried (Na,S04) .Evaporation affordeda yellow oil which was distilled (Kugelrohr; oven temp.80 "C; 15 mmHg) to give a pale yellow oil (4; R = Me)(290 mg, 78); 8, (CCI,) 6.8-6.1 (5 H, rn, H-2, -3, -4, -5.and -6), 5.34 (1 H, dcl, J 8 and 12 Hz, H-7), 2.82 (1 H, d ofq, J 8 and 6 H,, H-8), and 1.24 (3 H, d, J 6Hz, Me); 60(CDC1,) 194.03 (CO), 138.42, 136.95, 135.82, 134.06, 128.001 2 G. M. Whitesides, C. P. Casey, and J. K. Krieger, J . Anzer.Chem. SOC., 1971, 93, 13791976and 126.83 (olefinic), 45.59 (C-8), and 13.85 (Me); vwx(CC1,) 1 780m, 1660s, and 1640m cm-l; mle 134 (M+),119 (40y0), 105 (28), and 91 (100) (Found: C, 80.3; euro;3, 7.7.C,Hl,O requires C, 80.6; H, 7.5).8-AIZylcyclo-octa-2,4,6-t~ienone (4; R = aZZyl) .-Ally1 bro-mide (2 ml, 23.1 mmol; purified by fractional distillation)was added to a stirred solution of the enolate (2) (3 mmol)under argon at - 78 "C.The mixture was allowed to warmto room temperature over 2 h, and after 4 h the colour ofthe enolate had been discharged. After the work-up pro-cedure described above the crude product was purified bypreparative layer chromatography (methylene chloride).Finally, the resulting oil was distilled (Kugelrohr ; oventemp. 90 "C; 15 mmHg) to give a pale yellow oil (4; R =allyl) (297 mg, 74); SH(CC14) 6.8-6.1 (5 H, m, H-2, -3,-4, -5, and -6), 5.93-4.8 (4 H, m, H-7 and CHZCH,), and2.95-2.2 3 H, m, H-8 and (CH,CH:CH,); 8a(CDCl,)192.57 (CO), 138.47, 135.83, 135.73, 133.98, 128.70, 126.85,and 116.21 (olefinic), 50.92 (C-8), and 32.95 (CH,*CH:CH,) ;vm,.(CC1,) 1 780m, 1 670s, 1 640m, and 1 62Omcm-l; mle 160(M+, 53y0), 145 (29), 131 (30), 119 (loo), 117 (as), and 91(92) (Found: C, 82.0; H, 7.6. CllH1,O requires C, 82.5;H, 7.6).8-EthyZcycZo-octa-2,4,6-trienone (4; R = Et) .-Additionof ethyl iodide (2 ml, 26.8 mmol; purified immediatelybefore use by passage through basic alumina, activity 1)to a stirred solution of the enolate (2) (3 mmol) under argonat - 78 "C, followed by warming the mixture to - 5 "C over2 h, and further reaction at -5 "C for 10 h, caused completedischarge of the red colour of the enolate. The mixturewas worked up as described above to give a pale yellow oil,which was purified by layer chromatography.The platewas developed in methylene chloride, and the eluatedistilled (Kugelrohr; oven temp. 90 "C; 15 mmHg) togive a pale yellow oil (4; R = Et) (361 mg, 81); 8,-(CDCI,) 6.9-6.1 (5 H, m, H-2, -3, -4, -5, and -6), 5.36(2 H, m, CH,), and 0.86 (3 H, t, J 6 Hz, CH,) ; 80 (CDC1,)193.35 (CO), 138.75, 136.37, 135.6, 133.96, 128.64, and 126.7(olefinic), 53.13 (C-8), 21.86 (CH,), and 11.66 (CH,); vmx.(CCl,) 1 780m, 1 665s, and 1 620111 cm-1; mle 148 (M+, 36y0),133 (50), 119 (63), 105 (54), and 91 (100) (Found: C, 80.7;H, 8.3. C1,Hl,O requires C, 81.0; H, 8.2y0). When ethylbromide was used as alkylating agent under identicalconditions, preparative layer chromatography (methylenechloride) gave the following products in order of elution:ethoxycyclo-octatetraene (5; R = Et)2 (52 mg, 11) ;compound (4; R = Et) (71 mg, 16), and cyclo-octatri-enone (4; R == H) (80 nig, 22).8-Benzylcyclo-octa-2,4,6-trienone (4 ; R = PhCH,) .-Benzyl iodide l3 (0.4 ml, 3.24 mmol) was added under argonto a stirred solution of the enolate (2) (3 mmol) under argona t - 78 "C, and the mixture was allowed to warm to - 5 "Cover 3 h, by which time it had turned deep black.Themixture was worked up as above and the crude product waspurified by preparative layer chromatography (methylenechloridc) . The following products were obtained (in orderof elution) : cowzpound (4; R = PhCH,) (234 mg, 37) andcyclo-octatrienone (4; R = H) (183 mg, 51). The formerwas purified by Kugelrohr distillation (oven temp.90 "C;0.15 mmHg); 8~ (CCL,) 7.40-6.90br (5 H, s, aromatic),l3 V. hleyer, Ber., 1877, 10, 309; G. Kumpf, Annalen, 1884,224, 126.l4 J. Gasteiger, G. E. Gream, R. Huisgen, W. E. Konz, and U.Schnegg, Chern. Ber., 1971, 104, 2412.( 1 H, t, J 9 Hz, H-7), 2.60 (1 H, 4, J 9 Hz, H-8), 2.30-1.506.70-6.10 (5 H, m, H-2, -3, -4, -5, and -6), 5.80-5.20(1 H, m, H-7), 3.50-2.60 (2 H, m, CH,); 6~ (CDCI,) 192.42(CO), 138.42, 135.91, 135.85, 133.98, 128.94, 128.36, 126.92,and 126.12 (olefinic and aromatic), 52.78 (C-8), and 34.76(CH,); urn= (CC1,) 1 780m, 1 665s, and 1 620w cm-l; mje210 (M", 20), 167 (13), 165 (12), 132 (57), 119 (56), 105(58), and 91 (100) (Found: C, 85.4; H, 7.0. Cl,H,,Orequires C, 85.7; H , 6.7). Use of benzyl bromide inplace of benzyl iodide under identical conditions, followedby preparative layer chromatography (methylene chloride)afforded, in order of elution, cyclo-octatrienone (4; R = H)(172 mg, 48) and compound (4; R = PhCH,) (94 mg,Acetoxycyclo-octatetene (5; R = Ac) .14-To two separatesolutions of the enolate (2) (3 mmol) under argon at -78 "Cwere added different quantities of acetyl chloride (250 mg,3.2 mmol; and 115 mg, 1.5 mmol).The mixtures wereallowed to warm to - 5 "C over 2 h, by which time they wereblack and opaque. Work-up as above and extraction withether (rather than hexane) afforded crude products whichwere purified by preparative layer chromatography.Development and elution with methylene chloride afforded(in order of elution) acetoxycyclo-octatetraene (5 ; R =Ac) (125 mg, 26; and 46 mg, 9, respectively), whichshowed physical data identical with the values reported,l*and cyclo-octatrienone (4; R = H) (178 mg, 49; and130 mg, 36, respectively).R = C0,Et) .-Addition of ethyl chloroformate (328 mg, 3.2 mmol; and162 mg, 1.5 mmol) in two separate experiments to a solutionof the enolate (2) under argon at - 78 "C, followed by warm-ing to - 5 "C over 2 h, and the usual work-up and chromato-graphy as above, gave, in order of elution, the curbonate ( 5 ;R = C0,Et) (364mg, 63; and 164mg, 2876, respectively),and cyclo-octrienone (4; R = H) (negligible amounts; and225 mg, 62, respectively).The carbonate ( 5 ; R ==C0,Et) was distilled (Kugelrohr; oven temp.100 "C, 0.2mmHg); BE (CCl,) 6.2-5.5 (7 H, m, olefinic), 4.15 (2 H, q,J 7 Hz, CH,), and 1.30 (3 H, t, J 7 Hz, CH,); vrnax. (CC1,)1760s, 1680w, and 1 640w crn-l; A,,,. (C,Kl,) 279 nm(E 1 600); m/e 192 (M+) (Found: C, 68.5; H, 6.3. Cl,Hl,O,requires C, 68.7; H, 6.3).Reaction of the EnoZate (2) with Diphenyl Disu1plzide.-Diphenyl disulphide (210 mg, 1 mmol) in THF (5 ml) wasadded to a solution of the enolate (2) (0.8 mmol) in THF(14 ml) and HMPA (1.5 ml, 8.5 mmol) at -78 "C, and thesolution was allowed to warm to room temperature over0.5 11. After the usual work-up, the crude product waspurified by preparative layer chromatography (methylenechloride-hexane, 1 : 1). In order of elution were obtaineddiphenyl disulphide (58 mg, 27), 2,2-bis(phenylthio)ace-tophenone (10; R = PhS) (37 mg, 20), mp.97-99"(1it.,l6 98-99"), 2-phenylthioacetophenone l6 (9; R =PhS) (6.5 mg, 4), and cyclo-octatrienone (4; R = H)(12.5 mg, 12).Reactiosz of the EItzoZate (2) with Eenzeneselenenyl Chloride.--Benzeneselenenyl chloride (200 mg, 1.05 rnmol) in THF(5 ml) was added to a solution of the enolate (2) (0.8 mmol)in THF (7 ml) and HMPA (1.5 nil, 8.5 rnmol) a t -78 "C.The mixture was allowed to warm to room temperatureover 0.5 h, and was then worked up in the usual manner.Preparative layer chromatography two developments inl5 F. Weygand and H. J. Eestmann, 2. Natztrfovsch., 1955, 10th296.1G 0. Behaghel and H. Seibert, Ber., 1932, 65, 812.15).Ethyl Cyclo-octatetraenyl Carbonate (5 1842 J.C.S.Perkin Imethylene chloride-hexaiie (1 : l) yielded, in order ofelution, diphenyl diselenide (36 mg, 18), 2,2-bis(phenyl-se1eno)acetophenone (10; R = PhSe) (40 mg, 18y0, and2-phenylselenoacetophenone (9 ; R = PhSe) (21 mg, 11 yo)which showed similar spectral properties to the known l6sulphide (10; R = PhS) and was not further characterised.The diseleno-compound (10; R = PhSe) had m.p. 78-79"(from hexane), 611. (CDC1,) 7.95-7.0 (11 H, m, aromatic)and 5.76 (1 H, s, methine); vmax. (CC1,) 1 675s cm-l; A,,(95 EtOH) 246 nm (E 18 800) (Found: C, 55.6; H, 3.7.C,,H,,OSe, requires C, 55.8; H, 3.8).8-Phenylselenocyclo-octa-2,4,6-trienone (4 ; R = PhSe) .-Beiizeneselenenyl bromide 109 l 6 (3 mmol) was prepared at-78 "C in situ in THF (20 ml) from bromine (240 mg, 1.5mmol) and diphenyl diselenide (5.5 mg, 1.66 mmol).Asolution of the enolate (2) (3 mmol) cooled to -78 "C in ajacketed dropping funnel was added dropwise to the stirredbenzeneselenenyl bromide solution a t - 78 "C under argon.After addition of the enolate, the deep purple colour ofthe benzeneselenenyl bromide was completely discharged,and the resulting solution was pale orange. After theusual work-up the crude product was purified by preparativelayer chromatography (benzene) ; the following productswere obtained in order of elution: diphenyl diselenide(127 mg, 25), and 8-phenylselenocyclo-octatvienone (4;R = PhSe) (332 mg, 40), m.p. 78-79"; (from hexane)SH (CDC1,) 7.7-6.9 (5 H, m, aromatic), 6.8-5.4 (6 H, m,olefinic), and 4.42 (1 H, d, J 9 Hz, H-8), and a small signalat 4.62 (dd, J 6 and 3 Hz, assigned to the ring junctionproton(s) of the bicyclic valence tautomer (7; R = PhSe) ;vmx.(CHCl,) 1785m, 1660s, and 1615m cm-l; Lax. (95EtOH) 240sh (e 11 200) and 280 nm (5 500) ; nzle 276 (M+ for*OSe) (Found: C, 61.0; H, 4.6. C,,H,,OSe requires C, 61.2;H, 4.4).8-PhenylthiocycZo-octa-2,4,6-trienone (4; R = PhS) .-Theprocedure described for (4; R = PhSe) was used. Thecooled enolate (2) (2.08 mmol) in THF (20 ml) and HMPA(2.5 ml) was added dropwise to benzenesulphenyl chloride(300 mg, 2.08 mmol) (prepared by the method describedfor toluenesulphenyl chloride 17) in THF (20 ml) at -78 "Cunder argon. After the addition, the colour of the enolatewas discharged, and the mixture was stirred for 30 minwhile being warmed to room temperature.After the usualwork-up and extraction, the crude yellow solid product waspurified by preparative layer chromatography (methylenechloride) to give diphenyl disulphide (25 mg, 11 yo) and thephenylthio-compound (4; R = PhS) (126 mg, 26). Com-pound (4; R = PhS) was a very unstable solid, neverobtained completely pure; 8~ (CDC1,) 7.18 (5 H, m, aro-matic), 6.7P-6.31 (5 H, m, olefinic), 5.71 (1 H, t, J 10Hz, H-7), and 4.30 (1 H, d, J 10 Hz, H-8), and a small signalat 4.52 (dd, J 2 and 6.5 Hz) assigned to the ring junctionproton(s) in the bicyclic valence tautomer ( 7 ; R = PhS);vmaX. (CCI,) 1790m, 1670s, and 1615w cm-l; mJe 228(Mf, 20), 186 (8), 150 (40) 122 (56), 119 (38), and91 (100) (Found: M+, 228.061. C,,H,,OS requires M ,228.061).8-Bronzocyclo-octa-2,4,6-trienone (4; R = Br) .-To asolution of the enolate (2) (3 mmol) was added bromine(0.16 ml, 3 mmol) at -78 "C, and the solution was stirredfor 5 min. Work-up and extraction in the usual wayafforded a crude product which was purified by preparativelayer chromatography at 0 "C (methylene chloride). Thebromo-cowpound (4; R = Br) (306 mg, 51) was obtainedas a highly unstable pale yellow solid. It could not bepurified by crystallisation, and showed (CDCI,) 6.19-6.90(5 H, m, H-2, -3, -4, -5, and -6), 5.84 (1 H, dd, J 9 and 10 Hz,H-7), and 4.71 (1 H, d, J 9 Hz, H-8); vImx (CCl,) 1790s,1 677s, and 1 620s cni-l; A,,,. 225 nm (rel. intensity l . O ) ,245sh (0.73), 280sh (0.48), and 340 nm (ca. Pn/e 200and 198 (M+, 9) 119 (loo), and 91 (97) (Found:M+, 199.965 and 197.967. C,H,BrO requires M , 199.966and 197.968).We thank the S.R.C. for a studentship (to P. A. C.) andProfessor R. A. Raphael for his interest in this research.We are grateful to Roche Products Limited for support andto ilk-. M. J. Carter for a gift of benzenesulphenyl chloride.6/269 Received, 9th Februavy, 1976117 F. Kurzer and J. R. Powell, Ovg. Synth., Coll. Vol. IV, 1963,934
展开▼
