Lewis acid-catalyzed cycloaddition reactions of donor-acceptor cyclopropanes

The one-step diastereoselective synthesis of cis-2,5-disubstituted tetrahydrofurans via Lewis acid-catalyzed [3 + 2] cycloadditions of donor-acceptor (D-A) cyclopropanes and aldehydes is described. A detailed examination of the mechanism has been performed including stereochemical analysis and electronic profiling of both reactants. Experimental evidence supports an unusual stereospecific intimate ion pair mechanism wherein the aldehyde functions as a nucleophile and malonate acts as the nucleofuge. The mechanism facilitates the stereospecific synthesis of a range of optically active tetrahydrofuran derivatives from enantioenriched D-A cyclopropanes