Diastereoselective Synthesis of Trisubstituted Cyclopropanes by Palladium-Catalyzed Intramolecular Allylic Alkylation of α-Aryl Esters­

Abstract

We have developed a novel method for synthesizing trisubstituted cyclopropane derivatives by a palladium-catalyzed intramolecular allylic alkylation of α-aryl esters. By using α-aryl α-(methoxycarbonyl) γ-vinyl γ-lactones as substrates, decarboxylative formation of π-allylpalladium(II) intermediates followed by an intramolecular allylic alkylation of the ester enolates proceeded in the presence of 5 mol% of a palladium catalyst, producing 1-aryl-1-(methoxycarbonyl)-2-vinylcyclopropanes in good to excellent yields and high diastereoselectivities. The relative configuration of the major isomer was determined by transforming the product into a known intermediate of milnacipran synthesis. When we extended our method to asymmetric catalysis, we obtained methyl (1<i>S</i>,2<i>S</i>)-1-phenyl-2-vinylcyclopropanecarboxylate in up to 55% ee by using (<i>S</i>)-[2′-(diphenylmethoxy)-1,1′-binaphthalen-2-yl](diphenyl)phosphine as a chiral monodentate phosphorus ligand.