A highly regio-, diastereo- and enantioselective intramolecular cyclopropanation reaction of a racemic α-diazo ketone catalyzed by chiral ortho-metalated dirhodium(II) compounds

✍ Scribed by Julia Pérez-Prieto; Salah-Eddine Stiriba; Eduardo Moreno; Pascual Lahuerta

• Book ID: 104359637
• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 110 KB
• Volume: 14
• Category: Article
• ISSN: 0957-4166
• DOI: 10.1016/s0957-4166(02)00870-4

✦ Synopsis

A series of racemic dirhodium(II) compounds with two ortho-metalated aryl phosphine ligands in a head-to-tail arrangement Rh 2 (O 2 CR) 2 (pc) 2 (pc=ortho-metalated aryl phosphine) (1a-k) were tested in the regio-and stereoselective cyclopropanation of racemic 1-diazo-6-methyl-3-(2-propenyl)-5-hepten-2-one 2, which possesses two different reactive C C double bonds for a five-membered-ring formation. The complexes Rh 2 (O 2 CCH 3 ) 2 (pc) 2 {pc=[(C 6 H 4 )P(C 6 H 5 ) 2 ], [(p-CH 3 C 6 H 3 )P(p-CH 3 C 6 H 4 ) 2 ], and [(C 6 H 4 )P(C 6 H 5 )(C 6 F 5 )]} (1a-d) successfully enhanced the cyclopropanation of trisubstituted versus monosubstituted C C bonds to give an 80:20 selectivity ratio. The reaction occurred with excellent diastereoselectivity; the syn-products were the only stereoisomers observed in the whole series of the catalysts. Enantioenriched products were obtained when enantiomerically pure dirhodium(II) complexes were used.