Ene reactions of allylic tin compounds with singlet oxygen and with 4-phenyl-1,2,4-triazoline-3,5-dione

Abstract

Allylic tin compounds (I) react with singlet oxygen to give allylperoxystannyl compounds (II) by stannylallylation, stannylallyl hydroperoxides (III) by hydroallylation, and 4-stannyl-1,2-dioxolanes (IV) by rearrangement and cycloaddition. For example, 3-trimethylstannylprop-1-ene (I; R = R′= H; [graphic omitted] M = Me₃Sn) in CH₂Cl₂ at room temperature gives 25%II, 25%III and 50%IV; 1-tributylstannylcyclohex-2-ene (I; R–R′=–CH₂CH₂CH₂–; M = Bu₃Sn) in CH₂Cl₂ gives 66%II and 33%IV, but in MeOH–benzene, the yield of II is > 95%. The dioxolane IV appears to be a primary product of the reaction, and does not result from ring-closure of II, Under similar conditions, triethylsilylcyclohex-2-ene (I; R–R′=–CH₂CH₂CH₂–; M = Et₃Si) in CH₂Cl₂ shows only the hydroallylation reaction to give II.

Similar reactions occur with 4-phenyl-1,3,4-triazoline-2,5-dione. For example, 3-trimethylstannylprop-1-ene in CH₂Cl₂ gives 85%V and 15%VII, but in MeOH–benzene, the yield of V is 95%. Under [graphic omitted] the same conditions, triethylsilylcyclohex-2-ene gives 5%V, 70%VI, and 25% of the cycloadduct VII.

These reactions are discussed in terms of the usual mechanistic models for the ene reactions, and for the β-effect of organometallic groups.