Silane substituents chirality transfer

If the silicon atom of allylsilane is stereogenic, disappointing selectivities are obtained [1156], On the other hand, if the silicon substituents are chiral, a chirality transfer may be observed if the allylic group itself bears the asymmetry [54, 736] or asymmetric induction may be observed if another substituent of silicon is chiral [737, 1014], Chirality transfer in into-- or intramolecular reactions of allyl-silanes 2.78 with aldehydes is very efficient under TiCl4 catalysis however, from allylsilanes 2.79, a poor selectivity is observed [737, 1014] (Figure 6.53). More useful results were obtained by Nishitani and Yamakawa [1222] in the cyclization of 6.60, whose chiral ester is derived from (l/ ,25,5i )-phenmenthol 1.4 (R = Ph). The chiral auxiliaty is recovered after lactonization, but the absolute configuration of the cis lactones thus formed has not been determined (Figure 6.53). 

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