Reductive Reformatsky–Honda Reaction of α,β‐Unsaturated Esters: Facile Formation of 1,3‐Dicarbonyl Compounds and β‐Hydroxy Esters

Abstract

The reaction of tris(triphenylphosphine)-with diethylzinc (Et 2 Zn) easily afforded a rhodium-hydride complex that effects the 1,4-reduction of a,b-unsaturated esters to give rhodium enolates. Formation of the rhodium enolate is followed by transmetalation with the zinc species to give a Reformatsky-type reagent, and this reacts with various acid chlorides at the aposition to give b-keto esters. The Reformatsky-type reagent also reacts with various electrophiles such as aldehydes, ketones and acid anhydrides to give the corresponding products in which the electrophiles were introduced reductively at the a-position of a,bunsaturated esters.

Asymmetric Reductive Aldol-Type Reaction with Carbonyl Compounds Using Dialkyl Tartrate as a Chiral Ligand

“…However, this result confirmed that the approach would provide a promising route to such a cyclic compound, because a number of studies have reported on the enantioselective reductive aldol cyclization. 13,25,26) On the basis of previous results and various examinations of reaction conditions, 20,21) we proposed the following mechanism (Fig. 2).…”

“…Methyl 3-Hydroxy-2-methyl-3-phenylpropanoate (3a) 20,21) Each diastereomers of the title product (3a) were purified by column chromatography (AcOEt : hexane=2 : 3) and were obtained in 40% (39 mg; syn form) and 55% 20,21) Each diastereomers of the title product (3b) were purified by column chromatography (AcOEt : hexane=1 : 4) and were obtained in 36% (47 mg; syn form) and 48% yield (62 mg; anti form), respectively.…”

“…(syn-(2R,3R/2S,3S)-3d) A colorless oil; Methyl 3-Hydroxy-3-(4′-methoxyphenyl)-2-methylpropanoate (3e) 20,21) Each diastereomers of the title product (3e) were purified by column chromatography (AcOEt : hexane=1 : 4) and were obtained in 40% (45 mg; syn form) and 57% yield (64 mg; anti form), respectively.…”

“…(syn-(2R,3R/2S,3S)-3e) A colorless oil; Methyl 3-Cyclohexyl-3-hydroxy-2-methylpropanoate (3g) 21) Title product (3g) was purified by column chromatography (AcOEt : hexane=1 : 4) and obtained in 78% (73 mg 20,21) The crude solid of title product (3h) was washed with hexane and was obtained in 61% yield (82 mg …”

“…18) Based on their report, we reported Reformatsky-Honda reaction using BrCF 2 COOEt. 19) Furthermore, we recetnly reported a reductive aldol-type reaction of α,β-unsaturated esters with aldehydes and ketones to give the corresponding products in good to excellent yields by using RhCl(PPh 3 ) 3 and Et 2 Zn (Reformatsky-Honda reaction condition) 20,21) (Chart 1). We herein report an asymmetric reductive aldol-type reaction with various aldehydes and ketones.…”