Activation of donor–acceptor cyclopropanes under basic conditions: ring opening of 2-(p-siloxyaryl)cyclopropane 1,1-dicarboxylates with nitro compounds and other C-nucleophiles

Abstract

A new approach towards the ring opening of aryl-substituted donor–acceptor cyclopropanes (DAC) is proposed. 2-(p-Siloxyaryl)cyclopropane 1,1-dicarboxylates underwent a homo-Michael addition of nitro compounds promoted by TBAF and N-methylmorpholine. The transformation produces nitroalkyl-substituted malonates in high yields and has a wide substrate scope. Other C-nucleophiles such as malonates, 1,3-diketones, acetoacetates, and malononitrile also undergo this transformation smoothly. In contrast to the known activation of DAC promoted by Lewis acids, here the activation of DAC is metal-free and is performed under basic conditions. The proposed activation mode relies on fluoride-induced desilylation, affording an electron-rich phenolate anion. Such an increase in the donating properties of the aryl group of DAC facilitates the ring-opening of cyclopropane and the formation of the p-quinone methide intermediate. The reaction of the latter with nucleophiles leads to C–C bond formation providing target products. The presence of phenol, nitro, and carboxylate moieties allows subsequent selective transformations, including the preparation of lactam (2-piperidone) derivatives.