ENE REACTIONS OF ALLYLIC TIN-COMPOUNDS WITH SINGLET OXYGEN AND WITH 4-PHENYL-1,2,4-TRIAZOLINE-3,5-DIONE

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; [GRAPHICS] 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-trimethylstannyl-prop-1-ene in CH2Cl2 gives 85% V and 15% VII, but in MeOH-benzene, the yield of V is 95%. Under [GRAPHICS] 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 beta-effect of organometallic groups.