ortho-Metalated dirhodium(II)-catalyzed #alpha#-diazocarbonyl transformation. Diastereoselective cyclopropanation of menthyl-#alpha#-diazo-#beta#-keto ester and C-H insertion of #alpha#-diazo ester

摘要

ortho-Metalated rhodium(II) compound (1d_1) containing two metalated P(C_6H_5)-2(C_6F_5) and two acetates has successfully catalyzed cyclopropanation of methyl-2-diazo-3-oxo-6-heptanoate (4) to form cyclopropanes 6 and 7 with signficant cis-trans (30:70) diastereoselectivity. An enhanced performance of methyl-2-diazoundecanoate (5) cyclization has been achieved mediated by 2d_1 2d_4 catalysts, obrtaining 71 and 85%, respectivley, 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(C_6H_5)_2(C_6F_5) ligands in a head-to-tal 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 1d_(3endo-exo) and 1d_(1endo-endo) allows their structural assignment.