Reaction of Organoaluminium Reagents with Cyclopropylmethyl Acetates and 2-Vinylcyclopropane-1,1-dicarboxylate Esters

Ring-opening alkylation of cyclopropylmethyl acetates was studied. The acetoxyl group of 7-(1-acetoxyheptyl)norcarane is substituted by the alkyl group upon treatment with trialkylaluminium, but alkylation of trans-1-(1-acetoxyethyl)-2-phenylcyclopropane with trialkylaluminium gives rise to trans-5-phenyl-2-alkenes. The reaction of (1S,2S)-2-phenylcyclopropylmethyl acetate with trimethylaluminium resulted in the complete loss of optical activity to give racemic 4-phenyl-1-pentene. Alkylation of trans-1-(1-acetoxy-3-phenylpropyl)-2-vinylcyclopropane with trialkylaluminium proceeds under regioselective ring-opening to give 3-alkylated trans-8-phenyl-1,5-octadiene (selectivity 73–83%). The regio- and stereochemistry of homoconjugate addition to activated vinylcyclopropanes having a doubly carbonyl substituted ring carbon was studied. Trialkylaluminium on addition to diethyl 2-vinylcyclopropane-1,1-dicarboxylate in a 1,5-manner afford diethyl (2-alkyl-3-butenyl)propanedioate (over 96% selectivity). In contrast, the reaction of this cyclopropane with tetraalkylaluminiumlithium takes place in a 1,7-manner to give diethyl (trans-4-alkyl-2-butenyl)propanedioate with 88–92% selectivity. Clean regiocontrol of the reaction is observed in the methylation of ethyl exo-6-(trans-1-propenyl)-2-oxobicyclo[3.1.0]hexane-1-carboxylate with trimethylaluminium or tetramethylaluminiumlithium. Alkylation with trimethylaluminium proceeds with 86% inversion of the configuration at C(6) of the substrate, affording (2R*,3R*)-2-ethoxycarbonyl-3-[(S*)-trans-1-methyl-2-butenyl]cyclopentanone which is transformed into neonepetalactone.