Enolsilane, Aziridinyl

Adridinyl Enolsilanes Aziridinyl enolsilanes could also be activated for [4+3] cycloaddition, by using stoichiometric amounts of strong Brpnsted acids (S. K. Lam, S. Lam, P. Chiu, in prep.). Aziridinyl enolsilane 217 was treated with TfOH in dichloromethane and captured by furan at low temperature to give a moderate yield of cycloadducts 218 and 219 (Scheme 18.49), the yield suffering from... 

SCHEME 18.50 Cycloadditions of methyl-substituted aziridinyl enolsilanes 224 and 229 and dienes. 

SCHEME 18.51 Cycloadditions of enantiomerically enriched aziridinyl enolsilane 217. 

The reaction of substituted aziridinyl enolsilane 224 and furan also afforded good yields of cycloadducts with good diastereoselectivity (Scheme 18.50). Similar to the epoxy enolsilanes (Section 18.1.3.7), the cycloaddition of (Z)-enol-silane 229 and cyclopentadiene was stereospecific with respect to the enol geometry and yielded the corresponding endo and exo cycloaddition products. 

The species undergoing [4-1-3] cycloaddition in the aziridinyl enolsilane reaction is not the typical siloxyallyl cation, but is probably similar to the intermediate in the analogous reaction of epoxy enolsilanes, because the cycloaddition of enantiomerically enriched aziridinyl enolsilane 217 in nitro-ethane afforded cycloadducts with largely retention of enantiomeric purity (Scheme 18.51). The same reaction mediated by TfOH in dichloromethane gave cycloadducts with higher... 

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