Silicon nucleophiles allylic substitution

Oestreich and co-workers elaborated the 1,2-addition of silicon nucleophiles to aldehyde-derived imines (Scheme 19) [49]. As in the case of the related procedure for allylic substitution (Sect. 4.2), preformed chiral 6-membered NHC-copper(I)... 

Independent from the work of Oestreich and co-workers, the group of Shintani and Hayashi presented another example of NHC-copper(I)-catalyzed asymmetric allylic substitution of allylic phosphates by nucleophilic silicon (Scheme 28) [61]. The NHC precursor L23 in combination with CuCl and NaOH as base allowed for the enantioselective preparation of several a-chiral allylic silanes. The choice of base is cmcial as aUcoxides had a negative effect on the regioselectivity (not... 

Allylsilanes are intrinsically nonnucleophilic. We believe that addition of fluoride ion to an allylsilane forms a silicate anion, which can react at either end of the tc-system. Thus from a mechanistic viewpoint, substitution of an allylsilane under nucleophilic conditions is more appropriately considered an addition-elimination reaction with the terms Se2 and Se2 aptly representing the elimination process. For recent evidence of pentacoordinate silicate intermediates in fluoride ion catalyzed allylation using trimethylallylsilane, see a) M. Kira, M. Kobayashi and H. Sakurai, Tetrahedron Lett.. 28. 4081 (1987) b) M. Kira, K. Sato and H. Sakurai. J. Am. Chem. Soc.. 110, 4599 (1988) c) T. Hayashi, Y. Matsumoto, T. Kiyoi, Y. Ito, S. Kohra, Y. Tominaga and A. Hosomi, Tetrahedron Lett., in press d) H. Sakurai, Lewis Acid Character and Selective Reactions of Pentacoordinate Silicon Compounds, this volume. 

---