title: High selectivity from configurational match/mismatch in carbon-hydrogen insertion reactions of steroidal diazoacetates catalyzed by chiral dirhodium(II) carboxamidates.
abstract: 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.
authors.affiliation: Department of Chemistry, University of Arizona, Tucson, Arizona 85721, USA. mdoyle@u.arizona.edu
authors.forename: M P
authors.initials: MP
authors.lastname: Doyle
authors.forename: S B
authors.initials: SB
authors.lastname: Davies
authors.forename: E J
authors.initials: EJ
authors.lastname: May
mesh_terms: D001391:Azo Compounds / Q000737:chemistry; D002384:Catalysis; D008968:Molecular Conformation; D012238:Rhodium / Q000737:chemistry; D013237:Stereoisomerism; D013256:Steroids / Q000737:chemistry*
chemical_list: D001391:Azo Compounds; D013256:Steroids; D012238:Rhodium