P(RNCH2CH2)3N:: an efficient promoter for the direct synthesis of E-α,β-unsaturated esters

Upon reacting ethyl acetate or methyl propionate with a variety of aromatic aldehydes in the presence of 1.06-1.2 equiv. of the pro-azaphosphatranes, P(MeNCH2CH2)(3)N, P(i-PrNCH2CH2)(3)N or [P(i-PrNCH2CH2)(2)(NHCH2CH2)N at 40-50 degreesC for 2-6 h in isobutyronitrile, the corresponding alpha,beta -unsaturated esters were formed as the only products. Ethyl acetate reacts with aldehydes to form exclusively E-isomers while the higher homologue methyl propionate gives rise to a mixture of E and Z isomers with the former as the major product. When used as the solvent, methyl propionate selectively forms the E-alpha,beta -unsaturated ester. The reaction is not as successful for the preparation of alpha,beta -unsaturated ketones. (C) 2001 Elsevier Science Ltd. All rights reserved.