title: Catalytic asymmetric hydrogenation of 2,3,5-trisubstituted pyrroles.
abstract: Catalytic asymmetric hydrogenation of N-Boc-protected pyrroles proceeded with high enantioselectivity by using a ruthenium catalyst modified with a trans-chelating chiral bisphosphine PhTRAP. The ruthenium catalyst prepared from Ru(eta3-methallyl)2(cod) and (S,S)-(R,R)-PhTRAP in the presence of triethylamine was the most enantioselective for the asymmetric hydrogenation of methyl pyrrole-2-carboxylate, giving the desired (S)-proline derivative with 79% ee in 92% yield. Moreover, 2,3,5-trisubstituted pyrroles bearing a large substituent at the 5-position were hydrogenated with 93-99.7% ee. The asymmetric reduction of 4,5-dimethylpyrrole-2-carboxylate gave only all-cis isomer and created three chiral centers with high degree of stereocontrol in a single process. This is the first highly enantioselective reduction of pyrroles.
authors.affiliation: Department of Chemistry, Graduate School of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan. rkuwascc@mbox.nc.kyushu-u.ac.jp
authors.forename: Ryoichi
authors.initials: R
authors.lastname: Kuwano
authors.forename: Manabu
authors.initials: M
authors.lastname: Kashiwabara
authors.forename: Masato
authors.initials: M
authors.lastname: Ohsumi
authors.forename: Hiroki
authors.initials: H
authors.lastname: Kusano