A General and Robust Method for the Preparation of (E)- and (Z)-Stereodefined Fully Substituted Enol Tosylates: Promising Cross-Coupling Partners

Abstract

A robust method for preparing (E)- and (Z)-stereodefined fully substituted enol tosylates is described. α-Substituted β-keto esters undergo (E)-selective enol tosylations using TsCl–Me₂N(CH₂)₆NMe₂ as the reagent (method A, 13 examples; 63–96%) and (Z)-selective enol tosylations using TsCl–TMEDA–LiCl as the reagent (method B, 13 examples; 62–99%). A plausible mechanism for the (E)- and (Z)-enol tosylation selectivity is proposed. A ¹H NMR monitoring experiment revealed that TsCl coupled with TMEDA formed a simple N-sulfonylammonium intermediate.

Key words

stereocomplementary - stereodefined olefin - enol tosylate - tosyl chloride - TMEDA - diamine - NMR monitoring

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Oriyama’s group reported pioneering work on chiral-diamine-catalyzed desymmetric benzoylations of meso-diols with PhCOCl and speculation regarding the mechanism. Contrary to the present result, they proposed the corresponding N,N′-chelate-type intermediate; see
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