Highly Regio-, Diastereo-, and Enantioselective Rhodium-Catalyzed Intramolecular Cyclopropanation of (Z)-1,3-Dienyl Aryldiazoacetates.

Chiral cyclopenta[2,3]cyclopropa[1,2-c]pyran-4-ones have been synthesized via dirhodium(II)-catalyzed intramolecular cyclopropanation of (Z)-1,3-dienyl aryldiazoacetates. High regio-, diastereo-, and enantiocontrol were achieved using chiral dirhodium 2-phthalimide carboxylates. Preferential addition occurs at the 3,4- rather than the 1,2-double bond with the chiral dirhodium catalysts, although both outcomes occur with other transition-metal catalysts.