Three-membered ring formation reaction—III : Mechanism of the reaction of α-halogenoacrylic ester with organozinc compounds

The stereochemistry of ring formation in the reaction of α-halogenoacrylic ester with organozinc compounds was studied using β-deuterated α-halogenoacrylic ester. A quantitative study was made on the steric course of every step of the reactions involved in the synthesis of methyl β-deuterio-α-bromoacrylate-cis-d₁ starting from methyl propiolate. The mode of the CC double bond opening of methyl β-deuterio-α-bromoacrylate-cis-_d1 to form dimethyl 1 -bromo-2-propyl-cis-1,2- cyclopropanedicarboxylate-d₂ was confirmed to be cis and trans in a 50 to 50 ratio. Asymmetric syntheses for the cyclopropanedicarboxylic ester were possible, especially under the influence of chiral organozinc alkoxide system. A stepwise mechanism was postulated for the ring formation reaction.