BF3-OEt2 mediated thioester silylketene acetal additions to aldehydes are stereoconvergent and give high anti-syn ratios and good chemical yields. An acyclic transition state model was hypothesized in order to account for the observed selectivity. Theoretical methods (MNDO) were used to evaluate the ground-state conformations of thioester silylketene acetals and to model the acyclic transition states. Lewis acid mediated additions of thioester silylketene acetals to 2-phenylpropion-aldehyde (BF3-OEt2), O-benzyl lactic aldehyde (SnCl4), 2,3-0,O-dibenzyl glyceraldehyde (SnCl4), and 3-benzyloxy-2-methylpropionaldehyde (TiCl4) were found to be highly diastereoface selective so that three contiguous stereocenters could be established. With α-, β- , or α,β-alkoxy aldehydes, relative stereoselection (chelation) effectively controls internal stereolection. The ground state conformations of the chiral aldehydes were studied using molecular mechanics (MM2).

LEWIS ACID MEDIATED ALDOL CONDENSATIONS USING THIOESTER SILYL KETENE ACETALS / C.M.A. GENNARI, M.G. BERETTA, A. BERNARDI, G. MORO, C. SCOLASTICO, R. TODESCHINI. - In: TETRAHEDRON. - ISSN 0040-4020. - 42:3(1986), pp. 893-909.

LEWIS ACID MEDIATED ALDOL CONDENSATIONS USING THIOESTER SILYL KETENE ACETALS

C.M.A. GENNARI
Primo
;
A. BERNARDI;C. SCOLASTICO
Penultimo
;
1986

Abstract

BF3-OEt2 mediated thioester silylketene acetal additions to aldehydes are stereoconvergent and give high anti-syn ratios and good chemical yields. An acyclic transition state model was hypothesized in order to account for the observed selectivity. Theoretical methods (MNDO) were used to evaluate the ground-state conformations of thioester silylketene acetals and to model the acyclic transition states. Lewis acid mediated additions of thioester silylketene acetals to 2-phenylpropion-aldehyde (BF3-OEt2), O-benzyl lactic aldehyde (SnCl4), 2,3-0,O-dibenzyl glyceraldehyde (SnCl4), and 3-benzyloxy-2-methylpropionaldehyde (TiCl4) were found to be highly diastereoface selective so that three contiguous stereocenters could be established. With α-, β- , or α,β-alkoxy aldehydes, relative stereoselection (chelation) effectively controls internal stereolection. The ground state conformations of the chiral aldehydes were studied using molecular mechanics (MM2).
Settore CHIM/06 - Chimica Organica
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/177022
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