Assigning the stereochemistry of syn and anti β-trimethylsiloxy-α-trimethylsilyl alkanoic acid silyl esters using GIAO 1H NMR chemical shift calculations

Slim Hadj Mohamed, Mahmoud Trabelsi, Benoît Champagne

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Résumé

The stereostructure of β-trimethylsiloxy-α-trimethylsilyl alkanoic acid silyl esters synthesized by Bellassoued et al. [J. Org. Chem. 2001, 66, 5054–5057] using Mukaiyama aldol reaction has been reassigned using density functional theory NMR 1H chemical shifts calculations. It is now concluded that the major diastereoisomer is syn and the minor is anti. Within this assignment, for all silyl esters, δHa(anti) > δHa(syn), δHb(anti) < δHb(syn), and 3JHa-Hb (anti) > 3JHa-Hb (syn). Since the experimental assignment was based on the stereostructure (E/Z) of the cinnamic acid obtained by elimination of trimethylsilyl 3-phenyl-3-(trimethylsiloxy)-2-(trimethylsilyl)propanoate in the presence of TiCl4 and on the assumption that this elimination is anti stereospecific in acidic medium, one arrives at the conclusion that the elimination of syn and anti β-trimethylsiloxy-α-trimethylsilyl alkanoic acid silyl esters is not anti stereospecific.

langue originaleAnglais
Pages (de - à)436-440
Nombre de pages5
journalJournal of molecular structure
Volume1141
Les DOIs
Etat de la publicationPublié - 5 août 2017

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