ortho-Metalated dirhodium(II)-catalyzed α-diazocarbonyl transformation. Diastereoselective cyclopropanation of menthyl-α-diazo-β-keto ester and CH insertion of α-diazo ester

ortho-Metalated rhodium(II) compound (1d1) containing two metalated P(C6H5)2(C6F5) and two acetates has successfully catalyzed cyclopropanation of menthyl-2-diazo-3-oxo-6-heptanoate (4) to form cyclopropanes 6 and 7 with significant cis–trans (30:70) diastereoselectivity. An enhanced performance of methyl-2-diazoundecanoate (5) cyclization has been achieved mediated by 2d1 and 2d4 catalysts, obtaining 71 and 85%, respectively, of the 1,5-CH insertion product, trans-2-pentylcyclopentanecarboxylate (8) versus 1,2-elimination product, (Z)-2-undecenoate (9) (29 and 15%, respectively). The three possible diastereomers of catalyst (1d) which possess two ortho-metalated P(C6H5)2(C6F5) ligands in a head-to-tail configuration, with the two pentafluorophenyl groups in an endo–endo, endo–exo or exo–exo disposition have been separated by standard column chromatography. The X-ray structure analysis for two of these isomers 1d3endo–exo and 1d1endo–endo allows their structural assignment.