Lewis acid-mediated reactions of 1-cyclopropyl-2-arylethanone derivatives with diethyl 2-oxomalonate and ethyl 2-oxoacetate

TMSOTf-mediated reactions of 2-aryl-1-(1-phenylcyclopropyl)ethanones 1 with diethyl 2-oxomalonate 2 afford a novel method for the synthesis of spiro-γ-lactone derivatives 3 in good to excellent yields via a sequential reaction involving a nucleophilic ring-opening reaction of the cyclopropane by H2O, an aldol-type reaction and a cyclic transesterification mediated by Lewis acid. On the other hand, we found that TMSOTf-mediated reactions of 1-cyclopropyl-2-arylethanones 1 with ethyl 2-oxoacetate 4 could also provide the corresponding spiro-γ-lactone derivatives 5 in moderate yields along with another spiro-γ-lactone derivatives 6 derived from the reaction of 1 with two molecules of ethyl 2-oxoacetate. The plausible reaction mechanisms have also been provided on the basis of control experiments.