Enantioselective Carbonyl Ylide Formation/1,3-Dipolar Cycloaddition

Significance

Complementary to previous reports on related enantioselective carbonyl ylide cycloadditions (M. P. Doyle, D. C. Forbes Chem. Rev. 1998, 98, 911; H. Suga, K. Inoue, S. Inoue, A. Kakehi J. Am. Chem. Soc. 2002, 124, 14836), this communication reports an enantioselective intermolecular 1,3-dipolar cyclo­addition of a carbonyl ylide and an aromatic aldehyde as the dipolarophile. The reaction is catalyzed by a chiral dirhodium(II) catalyst and gives exclusively the exo product. The highest ee values are seen for electron-withdrawing benzaldehyde dipolarophiles. The enantioselectivity is also dependent on the substitution pattern at the ylide carbonyl (best with an aromatic ring), substitution at the α-position of the carbonyl ylide (best as H), and the length of the tether between the carbonyl and di­azo ester components of the ylide (best with a one-carbon tether).