Highly diastereroselective synthesis of dihydrofurans and dihydropyrroles via pyridine catalyzed formal [4+1] annulation

A pyridine-catalyzed ylide cyclization affording dihydrofurans and dihydropyrroles has been developed. In the presence of a catalytic amount of pyridine and Fe(Tcpp)Cl, alpha-ylidene-beta-diketones and alpha, beta-unsaturated imines react with diazoacetates providing dihydrofurans and dihydropyrroles respectively, in up to 96% yield with high diastereoselectivities.