An Easy, Efficient, and Completely Stereoselective Synthesis of (E)-α,β-Unsaturated Esters via Sequential Aldol-Type/Elimination Reactions Promoted by Samarium Diiodide or Chromium Dichloride

Abstract

(E)-Alpha,beta-unsaturated esters can be obtained with complete stereoselectivity by reaction of different aldehydes and ethyl dibromoacetate promoted by SmI(2) or CrCl(2). The transformation takes place as two sequential reactions: an aldol-type reaction and a beta-elimination reaction.

Synthesis of Indolines via a SmI2 Promoted Domino Nitro Reduction–Intramolecular aza‐Michael Reaction

“…Samarium diiodide has been shown to be effective in the coupling of aldehydes to dibromoacetic acid , ethyldibromoacetate and dichloroacetamide in which the elimination reaction proceeds with very high E diastereoselectivity. SmI 2 is a well‐known reducing agent of arylnitro groups to anilines ; thus, we envisaged a tandem reaction resulting in the corresponding indolines from aldehydes 2a , 2b , 2c , 2d , 2e in a one‐pot procedure.…”

Regio- and Stereocontrol in the Reactions of α-Halo-β,γ-enoates and α-O-Phosphono-β,γ-enenitriles with Organocuprates

“…The reaction crude material was filtrated over a small layer of silica gel to remove the palladium catalyst and then eluted with 50% Et 2 O/50% hexanes. Concentration in vacuo and purification (silica gel, 15% EtOAc/85% hexanes) gave a pale yellow oil ( 4.20−4.29 (m, 2H), 4.92 (dd, J = 0.9, 6.0 Hz, 1H), 1H),5.70 (dt,J = 0.9,7.3 Hz,1H); 13 C NMR (125 MHz, CDCl 3 ) δ 13.9, 14.0, 22.3, 27.6, 31.4, 61.9, 67.6, 126.1, 136.0, 147.2; mass spectrum m/z (relative intensity) EI 186 (0.20, M + ), 168 (4.5), 157 (1), 140 (1), 113 (45), 95 (66), 83 (6), 57 (100), 55 (11).…”

Manganese-Promoted β-Elimination Reactions: Totally Stereoselective Synthesis of (E)-α,β-Unsaturated Esters

“…This stereochemistry was also unambiguously confirmed by comparison of NMR data of compounds 2a-h with similar materials previously prepared. 13 This proposed methodology to obtain a,b-unsaturated esters is general: R 1 and R 2 can be varied widely. So, aliphatic (linear, branched, or cyclic), unsaturated, or aromatic a,b-unsaturated esters can be prepared starting When this process was carried out in the absence of TMSCl, no reaction took place.…”