Asymmetric hydrodimerization reactions of unsaturated carbonyl compounds mediated by $SmI_2$

Abstract

New chiral auxiliaries were synthesized from (S)-indoline-2-carboxylic acid. These chiral auxiliaries provided high stereoselectivities in asymmetric hydrodimerization of α, β -unsaturated amides. The asymmetric reductive homocoupling reaction at the 3-position of α, β -unsaturated amides derived from (S)-indoline with $SmI_2$ resulted in (3R,4R)-dialkyladipamide derivatives with extremely high diastereoselectivities (up to >99%). When the chiral auxiliary was changed from (S)-indoline derivative to (2S,3aS,7aS)-octahydroindoline derivatives, which were obtained by reduction of benzene ring of indoline to cyclohexane ring, the opposite configuration, (3S,4S)-diethyladipamide, was obtained. Also, new $C_2-symmetric$ chiral amine, derived from $[S-(R^*,R^*)]-(-)-bis(α -methyl-benzyl)$amine provided high stereoselectivity (up to 97:3) in asymmetric reductive homocoupling reactions of β, γ -unsaturated α -ketoamides at the 4-position. On the other hand, it has been found that the chemoselective reduction of a-keto moiety in β, γ -unsaturated α -keto amide can be achieved by quick addition of $SmI_2$ solution.