A search for maximal neighboring group participation in Solvolyses of allylic substrates. Ethanolysis of 2-(ω-alkylthioalkyl)-3-methyl-2-cyclohexenyl p-nitrobenzoates
摘要:
The solvolysis of 2-(omega-methylthioalkyl)- and 2-(omega-benzylthioalkyl)-3-methyl-2-cyclohexenyl p-nitrobenzoates 5 and 6 in 80 vol % ethanol includes several competitive reactions. Path k1 is a stepwise process (k(H)/k(D) = 1.18-1.20) which includes allylic cation 9 as a reaction intermediate, while path k2 involves a neighboring sulfur participation (k(H)/k(D) = 1.01 - 1.03) and formation of an intermediate cyclic sulfonium cation 10. Esters 5 and 6 solvolyze in 80% EtOH with a greater neighboring group participation than in 97% TFE. IL has been concluded that in solvolytic reactions of allylic substrates a pronounced neighboring group participation (k2/k1= 900) may occur only with very strong internal nucleophiles, and in solvents which can not form strong hydrogen bonds with these nucleophiles.