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.