A convenient reduction of activated olefins by zinc–copper couple

摘要

1. CHEM. SOC. PERKIN TRANS. I 1983 1219 A Convenient Reduction of Activated Olefins by Zinc-Copper Couple 6. Lucas Sondengam,' 2. Tanee Fomum, Georges Charles, and T. Mac Akam Department of Organic Chemistry, University of Yaounde, Cameroon ~~-Activated olefins of the types Ph,C=CXY, R2C=CXY, PhRCICXY, and RCH=CXY (where X and Y are electronegative substituents or one of them is a hydrogen atom) have been reduced to the corresponding saturated compounds in excellent yields by treatment with zinc-copper couple in boiling methanol. A number of reports have been made on the reductive pro- perties of the zinc-copper couple. Kupchan and Maruyama reported the reductive elimination of epoxides to give olefins in a one-step stereoselective reaction in which a cis-epoxide gave predominantly the trans-olefin, while trans-epoxides generated the cis-olefin as the major product.Further reduc- 0@ Ph tions of epoxides were carried out by Ekong et a12 These ICN workers also reported the reduction of a,B-unsaturated Ph/c=cHketones and diosphenolic compounds to the corresponding 'saturated 't compounds, notably in the reduction of anthothecol (1) and cedrelone (2). Other methods for the selective reduction of double bonds include the use of sodium borohydride on a,P-unsaturated acids and esters 3*4 and, in recent years, L-and K-selectride and t-butyl alcohol by Ph /OZEtFortunato and Ganem: 10 palladium-on-carbon and tri- ethyl-or tri-n-butyl-amine by Cortese and Heck: and Ph/ lithium amide by Melamed and Feit.' H We recently* reported the use of zinc-copper couple in (4)the stereospecific and quantitative reduction of carbon-carbon triple bonds to the corresponding olefins.Our method for reduction of the acetylenes was found to be much better than the palladium-catalysed reduction of acetylenes by coCortese and Heck; their method reduced e.g. hex-1-yne to give hex-l-ene as only 49 of a mixture of products, and the catalyst could further reduce the olefin to a mixture of hexane and other products, whereas with zinc-copper couple different acetylenes gave the alkene in near quantitative yield, 0 no other reduction products being formed.* As a continuation of our study of reactions with zinc-copper 'OAc couple, we have now found that activated olefins can be (6)conveniently and selectively reduced by this reagent to the (5) corresponding saturated compounds in near quantitative yields. Various activated olefins (7)--(18) were treated with zinc-copper couple in methanol under reflux for periods not exceeding 24 h.Work-up gave the saturated compound without problems those which arose in the low temperature Itwork (-78 "C)of Melamed and Feit 'and Fortunato and (7) (8) a; R=C-N3 Bruce (-70 "C)are avoided. b; R= CO,H Furthermore, we found no problem in reducing compounds with only one electron-withdrawing group such as (13) and (16), whereas similar compounds (3) and (4) could not be reduced by the Melamed and Feit method, which only works when there are two electron-withdrawing groups attached to the double bond.Also, ethyl cinnamate (lo), which was 0 0 reduced by the L-selectride method to a mixture of twenty- one compounds, is readily reduced in excellent yield to the corresponding saturated compound, no by-products being detected. We have also observed that compounds (11) (12 1 7 The term 'saturated 'is used in this paper in a limited sense and containing two conjugated double bonds with a conjugated refers to the saturation of the double bond being reduced even though X and Y are unsaturated functions both in the starting electronegative group, such as (8a) and (8b), are readily materials and in the products. reduced to the saturated derivatives. The range of com-pounds reduced in this way is given in the Table. RR'CFCXY -+ RRCH-CHXY We found that when the double bond was activated by a Me H 'C=C' AMe C02Me (13) (14) Ph /CNc=c H'--'Ph (16) CH=CHMe OH (17b) (18) lactone, as in 14,15-deoxybacunone (5) and dihydro-14,15- deoxygedunin (6), no reduction took place even over long periods and with large quantities of the couple.This is not due to steric hindrance in the vicinity of the double bond, however, as coumarin (17a) is similarly not reduced, while 3ethoxycarbonylcoumarin (17) is readily converted into the saturated derivative ;clearly an electron-withdrawing group between the double bond and the lactone carbonyl is neces- sary for the reduction to occur. Although the styrene chromophore is present in most of these compounds, it does not contribute to their reduction as shown by the fact that the double bond on the side chain in isoeugenol(17b) is unaffected. J.CHEM. SOC. PERKM TRANS. I 1983 Table. Reduction of olefins (8)-(18) by zinc-copper couple Amount used Product (1 mol) Time (h) yield (I 3.5 3 98 4.5 3 98 5.6 6 96 5.6 5 84 4.0 5 97 4.0 5 95 8 24 88 2.8 4 98 3.0 4 98 5.0 5 98 8.O 6 94 3.O 96 85 7 24 zinc dust; 30 g, 1 mol) were refluxed for 3 h in methanol (95, 100 ml). Work-up as above gave a crude product which was recrystallized from benzene to give tetrahydropiperic acid (0.97 g, 98), m.p. 95-96 "C; G(CDC13) 1.50-1.90 (4 H, m, CH2CH2CH2C02H), 2.30-2.80 (4 H, m, ArCHz CH2C02H),5.85 (2 H, s, OCH20), 6.60 (3 H, s, Ar), and 9.5 (1 H, br s, C02H, disappears on deutriation).Similarly piperine (1 -piperoylpiperidine) (8a) (1 g, 0.0035 mol) and zinc-copper couple were refluxed for 3 h. Work-up as usual gave a crude product which was hydrolysed to tetra- hydropiperic acid. 1,5-Diphenylpentan-3-one.-l,5-Diphenylpenta-l,4-dien-3-one (12) (1 g, O.Oo40 mol) was refluxed with zinc-copper couple (prepared from 30 g of zinc dust) in methanol-water (3 :1; 120 ml) for 5 h. Work-up gave a crude product which was passed through a silica-gel column and then recrystallized (methanol) to give 1,5-diphenylpentan-3-one(0.96 g, 95), m.p. 67-70 "C. 2,3-Diphenylpropionitrile.-2,3-Diphenylacrylonitrile (16) (1 g, 0.0048mol) and zinc-copper couple (30 g, 1 mol of zinc dust) were refluxed in methanol (95; 100 ml) for 5 h.After usual work-up, the crude product was passed through a silica-gel column and then recrystallized (hexane) to give 2,3-diphenylpropionitrile (0.99 g, 98), m.p. 66-68 "C. 3,3-Diphenyl-2-phenylsulphonylpropionitrile.-3 ,3-Diphenyl-Experimental 2-phenylsulphonylacrylonitrile9g (14) (1 g, 0.0028 mol)Zinc-copper couple was prepared as indicated el~ewhere.~*~ and zinc-copper couple (30 g of zinc dust) were refluxed in M.p.s were taken on a Kofler hot-stage apparatus and are uncorrected. Refractive indices were taken on a universal refractometer. 'H N.m.r. spectra were taken on a Perkin-Elmer R12 B spectrometer with deuteriochloroform as solvent, unless otherwise stated, and tetramethylsilane as internal standard.The n.m.r. data are given as 6 values. Wherever used, silica gel for columns refers to Merck silica gel, mesh 0.0634.200 nm. Products were isolated in all cases by the following procedure :the exhausted zinc-copper couple was filtered off (filter paper) and repeatedly washed with methanol (the reaction solvent); the filtrate was then diluted with distilled water and extracted with either chloroform or methylene dichloride (3 x 50 ml). The combined extracts were dried (Na2S0, or MgS0,J and evaporated under reduced pressure. Tetrahydropiperine and Tetrahydropiperic Acid.-Piperic acid (8b) 5-(3,4-methylenedioxyphenyl)penta-2,4-dienoic acid (1 g, 0.0045mol) and zinc-copper couple (prepared from methanol-water (3 :1) for 4 h.Work-up gave an oily product which was recrystallized from ethanol to give the propionitrile (0.99 g, 98),m.p. 170-172 "C; G(CDC13) 4.75 (1 H, d, Ph2-CHCH), 5.05 (1 H, d, Ph2CHCH), 7.35 (10 H, s, Ar), and 7.10-7.80 (5 H, m, Ar). 2-Benzoyl-3,3-diphenylpropionitrile.-2-Benzoyl-3,3-di-phenylacrylonitrile 9b (15) (1 g, 0.003 mol) was refluxed with zinc-copper couple (30 g of zinc dust) in methanol-water for 4 h. After usual work-up, the 2-benzoylpropionitrile was obtained as an oily product (0.99 g, 98) which did not crystallize. G(CDC1,) 2.30 (3 H, s, ArCH3), 3.50 (1 H, d, Ph2CHCH), 4.1 (1 H, d, Ph2CHCH), and 6.90-7.80 (14 H, m, Ar). Dihydro-3-ethoxycarbonylcoumarin.-3-Ethoxycarbonyl-coumarin 9c (17) (0.8 g, 0.0036 mol) was refluxed with zinc- copper couple (30 g of zinc dust) in methanol-water for 6 h.J. CHEM. soc. PERKIN TRANS. I 1983 Usual work-up gave a crude product which was passed through a silica-gel column to afford an oil (0.76 g, 94) (Found: C, 65.45; H, 5.45; 0, 29.1 C12H1204 requires C, 65.44; H, 5.49; 0,29.06). G(CDC13) 1.23 (3 H, t, CHZCH,), 2.10-2.40 (4 H, m, methylene H),3.60-4.40 (1 H, m, 349, and 7.10 (3 H, m, Ar). Ethyl 3-Phenylpropionate.-Ethyl cinnamate lo (10) (1 g, 0.0056 mol) was refluxed with zinc-copper couple in methanol for 5 h. After work-up, the product was distilled under reduced pressure. An oily colourless liquid was collected between 120 and 124 "C 25 mmHg (0.85 g, 84), nD 1.4960 (lit.," nD 1.4954). 5-Phenylpentunoic Acid.-5-Phenylpenta-2,4-dienoic acid lo (9) (1 g, 0.0057 mol) was refluxed with zinc-copper couple in methanol-water (3 : 1) for 6 h.The isolated oily crude product (0.98 g, 96) did not crystallize from any available solvent. G(acetone) 1.10-1.60 (4 H, m, ArCH2CH2CH2CH2C02H), 2.20-2.80 (4 H, m, ArCH2CH2CH2CH2C02H), and 7.30 (6 H, d, Ar and OH which disappeared on deuteriation). Dihydr0fagaramide.-Fagaramide (N-isobutyl-3,4-methyl-enedioxycinnamamide) (1 1) (1 g, 0.004 mol) was refluxed with zinc-copper couple in methanol-water (3 : 1) for 5 h. Usual work-up gave a crude product (0.98 g, 97) which was recrystallized from acetone to give dihydrofagaramide, m.p.102-104 "C. G(CDC13) 0.83 (3 H, s, Me), 0.93 (3 H, s, Me), 1.40-1.96 (1 H, m, CH), 2.28-2.60 (2 H, m, CH2), 2.80- 3.18 (4 H, t, ArCH2CH2), 5.90 (2 H, s, 0CH20), and 6.80 (3 H, s, Ar). Dihydr0veprisine.-Veprisine l2 (2,6-dihydro-7,8-dimeth-oxy-2,2,6-trimethylpyrano3,2-cquinolin-5-one)(1 8) (1 g, 0.003 mol) was refluxed with zinc-copper couple in methanol (100 ml) for 96 h. Usual work-up gave an oily crude product (0.96 g) which was passed through a silica-gel column to give a solid compound which was recrystallized from ethyl acetate-n-pentane to give dihydroueprisine (0.85 g, 85), m.p. 154-156 "C (Found: C, 67.3; H, 6.9; N, 4.65; 0, 22.2. C17HZ104N requires C, 67.31; H, 6.98; N, 4.0; 0, 21.10). G(CDC1,) 0.90 (6 H, d, Me x 2), 1.45 (3 H, t, CH2), 2.8 (2 H, t, CH3, 3.86 (3 H, s, NMe), 3.95 (6 H, s, OMe, x 2), 6.87 (1 H, d, Ar), and 7.82 (1 H, d, Ar).Methy2 IsovaZerute.-Methyl 3,3-dimethylacrylate (1 3) (1 g, 0.008 mol) was refluxed for 24 h with zinc-copper couple in methanol (200 ml). Usual work-up gave methyl iso-valerate (0.90 g, 88); nD 0.8800 (lit.," nD 0.8808). Attempted Reduction of Coumarin (17a).-Coumarin (1 g, 0.007 mol) was treated with zinc-copper couple in boiling methanol for 24 h. Work-up gave starting material (0.95 g) as shown by the spectral data and m.p. Attempted Reduction of Isoeugeno 1 (2-Methoxy-4-prop-l- enylphenol) (17b).-Isoeugenol (1 g, 0.006 mol) was treated with zinc-copper in boiling methanol for 120 h. Work-up gave starting material (0.96 g).References 1 S. M. Kupchan and M. Maruyama, J. Org. Chem., 1971, 30, 1187. 2 D. E. U. Ekong, J. I. Okogun, and B. L. Sondengam, J. Chem. Soc., Perkin Trans. I, 1975, 2118. 3 J. J. Eisch and A. M. Jacobs, J. Org. Chem., 1963,2145. 4 N. Prentice, L. S. Cuendet, and F. Smith, J. Am. Chem. Soc., 1956,4439. 5 J. M. Fortunato and Bruce Ganem, J. Org. Chem., 1976, 41, 2194. 6 N. A. Cortese and R. F. Heck, J. Org. Chem., 1978,43, 3985. 7 Uri Melamed and Ben Ami Feit, J. Chem. Soc., Perkin Trans. I, 1980, 1267. 8 B. L. Sondengam, G. Charles, and T. M.Akam, Tetrahedron Lett., 1980, 1069. 9 These compounds were synthesized by one of us (G. C.) follow- ing procedures described in (a)Bull. SOC.Chim. Fr., 1962, 1559; (6) idem., 1962, 1566; (c) idem., 1962, 1573. 10 F. G. Mann and B. C. Saunders in ' Practical Organic Chemistry,' 4thedn., Longmans, London, 1973, pp. 237, 279. 11 R. C. Weast and S. M. Selby, ' Handbook of Chemistry and Physics,' 4th edn., The Chemical Rubber Co., Ohio, 1966-67, 441 14. 12 J. F. Ayafor, B. L. Sondengam, and B. Ngadjui, Tetrahedron Lett., 1980, 3293. Received 28th July 1982 ;Paper 2/ 1297