Michael addition of N-nitroacetyl derivatives 1 of proline esters using KF under phase-transfer catalysis resulted in the formation of adducts 3-9 with chemical yields ranging from 40-90% (Scheme). Stereoselectivity of up to 51 % was obtained on addition of benzyl N-(nitroacety1)-L-prolinate (la). The absolute configuration at the newly created chiral centre was established in the case of 9 by carrying out a reductive acylation and comparing the product 10 with an authentic sample of ethyl N-(05-ethyl N*-acetyl-L-glutam-l-yl)-L-prolinate (L,L-~O).
Introduction. -In the last few years, there has been a spate of research publications on the use of aliphatic nitro compounds as building blocks for the synthesis of various biologically important molecules. The popularity of nitro compounds can be ascribed mainly to two reasons. First, under suitable conditions, it is possible to construct a C-C bond stereoselectively at the C(a) of nitroalkanes: various standard reactions were used for this purpose such as Michael addition [ 11, Henry reaction [2], alkylation [3], etc. The second important reason is that the NO, group can be transformed under mild conditions into other useful functional groups like amine, oxime, hydroxylamine, ketone, carboxylic acid, [4], etc. Our own group has been involved in exploring the possibility of using the nitroacetyl group as a peptide synthon [5-71. The underlying concept is to synthesise ')