Influence of the Substituents on the Opening of Silylepoxy Alcohols: 5--Cyclization Towards Tetrahydrofurans Vs. Unexpected Side Reaction Leading to Tetrahydropyrans

Overview

Journal Molecules

Publisher MDPI

Specialty Biology

Date 2021 Dec 10

PMID 34885968

Authors

Carlos Diez-Poza

Asuncion Barbero

Affiliations

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Abstract

The regioselective ring opening of epoxy alcohols is an effective method for the synthesis of different types of oxacycles. The 5- opening being preferred vs. the 6- mode, according to Baldwin rules, the use of silyl-substituted oxiranes has been reported as a possible method to favor the 6- cyclization. However, there is a need for a detailed study on the different factors (structural factors, catalyst nature or conditions) that influence this process. In this paper, the acid-catalyzed cyclization of epoxysilyl alcohols was studied, focusing on the effect of substituents and reaction conditions on the outcome of the process. Two types of heterocycles (tetrahydrofurans or tetrahydropyrans) were selectively obtained depending on the structure of the initial epoxysilyl alcohol. Interestingly, cyclization of hindered epoxysilyl alcohols mainly proceeds through an unexpected side reaction, which implies a previous isomerization to an aldehyde. A mechanistic proposal for the formation of the different products is presented.

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