Regioselective Nucleophilic Addition to Carbonyl Ylide Intermediates:  A Novel Diastereoselective Synthesis of Cycloalkyl Fused Furan-3-ones

A range of cis-fused hexahydro-1-benzofuran-3(2H)-one or tetrahydro-2H-cyclopenta[b]furan-3(3aH)-one ring systems was synthesized by the rhodium(II) acetate catalyzed reaction of α-diazo carbonyl compounds in the presence of various oxygen, nitrogen, and sulfur nucleophiles. A double-nucleophilic addition was possible by using an excess of α-diazo ketone. These reactions proceeded with complete diastereoselectivity, and the stereochemistry was confirmed by the single-crystal X-ray analysis. This process discloses the first example of tandem cyclization−nucleophilic addition reaction.