Synthesis and Reactions of α-Chloro-β,γ-unsaturated Esters. 1

Article abstract of DOI:10.1021/jo00299a034

Four new α-chloro-β,γ-unsaturated esters were prepared in good yield by the reaction of hypochlorous acid with substituted ethyl 2-butenoates.Reaction of these substituted allylic chlorides with several nucleophiles has been investigated.Thiophenol in the presence of aqueous sodium hydroxide react with ethyl 2-chloro-3-methyl-3-butenoate (2) to give 6, whereas ethyl 2-chloro-2,3-dimethyl-3-butenoate (1) is unreactive.Tertiary allylic chlorides 1, 3 and 4 react with secondary amines to give exclusive abnormal S_N2 reaction products.With benzylamine abnormal S_N2 substitution is followed by cyclization to give 1-benzyl-3-pyrrolin-2-ones.While ethyl lithioacetate reacts with 1 to give acylation product 18, sodium diphenylmethide in liquid ammonia undergoes alkylation on the tertiary carbon possibly by an electron-transfer reaction pathway.Lithio-1,3-dithiane reacts with 1 to give 2,3-dimethyl-6,10-dithiaspiro<4,5>dec-2-en-1-one (20) via a two-step process, viz., acylation followed by anovel variation of the intramolecular abnormal S_N2 reaction.Raney nickel desulfurization of 20 gave 2,3-dimethyl-2-cyclopenten-1-one.Synthetic and mechanistic implications of these results are discussed.