High selectivity from configurational match/mismatch in carbon-hydrogen insertion reactions of steroidal diazoacetates catalyzed by chiral dirhodium(II) carboxamidates.

Diazo decomposition of steroidal diazoacetates, where the point of attachment is the 3-position of the steroid A-ring, catalyzed by chiral dirhodium(II) carboxamidates results in products from carbon-hydrogen insertion in high yield and selectivities. Use of S-configured catalysts shows a distinctive preference for insertion into the 3-position to form beta-lactone products. The R-configured catalysts direct insertion preferentially to the equatorial C-H bond at the 2-position. Substituents or functional groups at the 5/6-position prevent C-H insertion from taking place at the 4-position. Even in the best case with the 5/6-positions fully saturated, however, insertion into the 3-position remains competitive with insertion into the 4-position. Corresponding 3-substituted phenyldiazoacetates give only beta-lactone products, and selectivity here is highest with chiral dirhodium(II) prolinate catalysts. A model is presented to explain these results. Overall, this methodology is versatile for functionalization of the steroid A-ring at positions 2 and 3.