REGIOSELECTIVE AND DIASTEREOSELECTIVE ENE REACTION OF TRIAZOLINEDIONE WITH VINYLSILANES

The one reaction of 4-methyl-1,2,4-triazoline-3,5-dione (MTAD) with vinylsilanes 1 has been investigated. In all cases studied, only hydrogen abstraction geminal to the silyl group with formation of triazolidinediones 3 occurred, irrespective of the number and size of the substituents at the double bond. A mechanism with an aziridinium imide as intermediate is proposed to explain the observed regioselectivity and diastereoselectivity. For the former we invoke preferential cleavage of the C-N bond proximate to the silyl substituent on the aziridine ring, for the latter steric repulsion between the adjacent silyl and alkyl group controls the observed E-type stereochemistry. A new synthetic approach to the trisubstituted vinylsilane 1e based on reductive lithiation of the corresponding vinyl sulfide is described.