The Stereoselective Synthesis of Conjugated Allylsilanes

Abstract

2-trimethylsilylethylidenetriphenylphosphorane (5) (Seyferth-Wittig reagent) reacts stereoselectively with the carbonyl compounds 6a-f to give the conjugated allylsilanes 7a-f, each as a mixture of E-and Z-isomers. The stereoselectivity of reactions of E-cinnamaldehyde (6c) with 5 has been investigated at different temperatures. A successful E-stereoselective synthesis of 7c was achieved by reacting 5 with E-cinnamaldehyde (6c) under the conditions of a Wittig-Schlosser modification reaction.Structures of the allylsilanes 7a-f were deduced by compatible analytical and spectroscopic (IR, 1 H NMR, 13 C NMR, and GC/MS) measurements. An assignment of the E:Z ratios of 7a-f is based on their 1 H NMR spectral data.