Abstract
Treatment of N-bromosuccinimide (NBS) with (carboethoxymethylene) triphenylphosphorane (1) in CH2Cl2 followed by the addition of an alcohol in the presence of manganese dioxide under ultrasonic irradiation constitutes a stereoselective one-pot procedure for the preparation of Z-configured α–bromo-α,β-unsaturated esters in good to excellent yield.
Highlights
The Wittig reaction is one of the most powerful and attractive methods for the construction of various alkenes [1]
In this paper we describe a one-pot methodology for the synthesis of (Z)-α–bromo-α,β-unsaturated esters using the above procedure
Due to our continuing interest in one-pot procedures [10,11], which convert multi-step reactions into economically and environmentally favored one-pot processes, we decided to combine the halogenation of an ylide, the oxidation of an alcohol with the cheap reagent MnO2 as a oxidant and a subsequent Wittig reaction into a one-step procedure
Summary
The Wittig reaction is one of the most powerful and attractive methods for the construction of various alkenes [1]. The synthesis of α–trifluoromethyl-α,β-unsaturated esters was based on trifluoromethylation of α–iodo-α,β-unsaturated esters [4] as well α-bromo-α,β-unsaturated esters [5] They are usually prepared by the Wittig reaction of aldehydes with haloylides [6,7] and condensation of aldehydes with halo-phosphonates in the presence of a base [8]. Taylor [9] described the development of an in situ alcohol oxidation-Wittig reaction using (carboethoxymethylene)triphenylphosphorane and manganese dioxide to produce α,βunsaturated esters. This method avoids the most common problems associated with the handling of Molecules 2010, 15 intermediate aldehydes, which are often difficult to isolate due to their volatility, toxicity, penchant to polymerize or facile hydration [9], and unsuitable for use as substrates. In this paper we describe a one-pot methodology for the synthesis of (Z)-α–bromo-α,β-unsaturated esters using the above procedure
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