Diastereoselectivity in the TiCl4-mediated aldol reaction of cyclic dienylsilyl ethers

One-Pot Synthesis of Lactams Using Domino Reactions: Combination of Schmidt Reaction with Sakurai and Aldol Reactions

“…The sole formation of 26a would require the dominating intermediacy of anti - 38 , which does not appear to be greatly favored, because of the steric interaction between bulky aldehyde side chain and cyclohexene ring, relative to the alternative syn - 38 , leading to 26b (not observed). In contrast to these results, Barner observed the inversion of stereoselectivity from anti to syn in Mukaiyama aldol reaction of pulegone with bulky aldehydes, which is inconsistent with the observed increase of anti -selectivity obtained with increasing bulk from 21 to 22 21. Our results therefore suggest that the domino Sakurai/aldol/Schmidt reaction does not involve a Mukaiyama-type aldol reaction and an open transition state.…”

Coupling of Organic Halides with Carbonyl Compounds Promoted by SmI2, the Kagan Reagent

“…Except in the rare case of the intramolecular reactions disclosed in Scheme , entry a, and Scheme , organosamariums add 1,2 to enones (Scheme , entry b). , However, 1,4-addition is feasible, if carried out under SGR conditions in the presence of CuI−P(OEt) 3 , CuBr-Me 2 S, or CuBr- Me 3 SiCl in THF−HMPA 56 (Scheme , entry b; Scheme , compare entry d to entries b and c; and Scheme ). Intramolecular addition has been efficiently achieved, however, with α,β-unsaturated esters (section 5.1.2).…”

Investigations into Transition‐State Geometry in the Mukaiyama Directed Aldol Reaction

“…Similar cyclic transition‐state structures in the Lewis acid induced Mukaiyama aldol reaction between a silyl enol ether or a ketene silyl acetal and an aldehyde were proposed by Chan et al.,31 Barner et al.,17 Helmchen et al.,32 and Yamamoto and co‐workers 18. In these proposals, the metal is coordinated to both the aldehyde and enolate oxygen atoms, and a halide ion then attacks the silicon atom to create a bicyclic transition‐state structure.…”

“…Titanium tetrachloride catalyzed reactions of cyclic, cross‐conjugated dienylsilyl ethers with aldehydes were investigated by Barner et al 17. It was shown that the steric demand of the aldehyde plays a critical role in determining the stereoselectivity (Scheme ).…”