Corner opening of cyclopropanes by mercury(II) and thallium(III) and transmetalation of the intermediate organomercurials. A novel, stereoselective approach to cyclobutanes and cyclopropanes

Abstract

The reactivity of the two isoelectronic cations (Hg2+ and T P ) toward the cyclopropane ring is compared, and further evidence for the exclusive corner selectivity for Hg2+ is provided by isotope labeling. Cleavage of cyclopropyl derivative 1 with Hg(NO3)2, followed by KBr quenching, afforded the stable, rearranged organomercurial 3, whose transmetalation has been studied. Whereas reaction of 3 with Pd(I1) afforded lactol 4, treatment with MezCuLi resulted in the formation of cyclobutanol derivative (3 - 29); analogous conjugate addition has also been accomplished (32 - 35). Similarly, the organomercurial 22, obtained from 21 as the major product on the Hg(I1)-mediated ringopening, reacted with MezCuLi or AlC13 to give the ring-closure product 21. These reactions representa novel method for the stereoselective construction of four- and three-membered rings. The stereochemistry of the key steps of these transformations has been established by using stereospecifically deuterated substrates lb, 3b, 21b, and 22b.