trans-Directing ability of amide groups in cyclopropanation: application to the asymmetric cyclopropanation of alkenes with diazo reagents bearing two carboxy groups.

Book: M. P. Doyle, M. A. McKervey, T. Ye Modern Catalytic Methods for Organic Synthesis with Diazo Compounds: From Cyclopropanes to Ylides; Wiley-VCH: New York, 1998. Comment: The authors propose an intriguing mechanistic pathways to explain the selectivity in the cyclopropanation with diazo reagents bearing two carboxy groups. It is proposed that the chiral rhodium complex preferentially binds to one face of 1, thereafter the amide substituent acts as a “trans-directing group” and promotes the formation of only one diastereomer. The enantioselectivity is shown to depend on both the ligand used and the substituents on the amide nitrogen. The yields are moderate to good for a variety of alkenes, although aliphatic olefins give poor results. Derivatizations of the resulting products, such as reduction, ring opening and esterification are demonstrated. R1 = OBu, Ph, Ar, Hetar, styryl R2 = H, Me 14 examples 24–92% yield 84–97% ee [Rh2(S-nttl)4] (1 mol%)