α,β-Unsaturated diesters:: radical acceptors in dialkylzinc-mediated tandem radical addition/aldol condensation.: A straightforward synthesis of rac-nephrosteranic acid

The sequence involving conjugate radical addition/aldol condensation/lactonization is a high yielding route to di- and trisubstituted gamma-lactones starting from fumaric or maleic diesters. The reactions are mediated with dialkylzincs. The domino process relies on the ability of dialkylzinc to transform alpha-alkoxycarbonylalkyl radicals into zinc enolates. Compared to diethylzinc, dimethylzinc enables the use of a wider range of alkyl radical precursors. In addition, dimethylzinc is a convenient source of methyl radical, which leads to a straightforward synthesis of methylated derivatives related to alpha-methyl-paraconic acids. (c) 2006 Elsevier Ltd. All rights reserved.