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, ¹H NMR, ¹³C NMR, and GC/MS) measurements. An assignment of the E:Z ratios of 7a–f is based on their ¹H NMR spectral data.

Keywords:

• Allylsilanes
• Seyferth–Wittig reagents
• structure elucidation
• Wittig–Schlosser modification

Acknowledgments

This work is considered as “Organophosphorus Chemistry 35” for part 34. cf. ref. 1.

H. A. A. Yosef is grateful to the German Academic Exchange Service for the award of a fellowship, and M. R. H. Mahran is profoundly indebted to the Alexander von Humboldt-Stiftung (Federal Republic of Germany) for the generous donation of HPLC Equipment (Perkin-Elmer, system 1022, model 135 C).

Notes

^a The low yield may be attributed to the low b.p. and the loss during the chromatographic process and evaporation of eluent; cf. ref. 7 and 8.

^bCf. ref. 9 and 25.

^aE:Z ratios were determined from ¹H NMR data.