Abstract
Tri- or tetrasubstituted furans have been prepared from terminal activated olefins and acyl chlorides or anhydrides by a multicomponental convergent synthesis mode. Instead of stoichiometric nBu3P, only catalytic nBu3P or nBu3P=O is needed to furnish the furans in modest to excellent yields with a good functional group tolerance under the aid of reducing agent silane. This synthetic method features a silane-driven catalytic intramolecular Wittig reaction as a key annulation step and represents the first successful application of catalytic Wittig reaction in multicomponent cascade reaction.
Highlights
The Wittig reaction [1–4] provides a powerful tool for convenient construction of carbon-carbon double bonds in synthetic chemistry
The catalytic proposed to rationalize the formation of tetra-substituted furans 3 (Scheme 5, left)
A convergent synthetic method for tri- or tetra-substituted furans has been developed by catalytic phosphine mediated multicomponental cascade reactions
Summary
The Wittig reaction [1–4] provides a powerful tool for convenient construction of carbon-carbon double bonds in synthetic chemistry. Most well-designed phosphines, especially chiral phosphine reagents [9–15], are very expensive and high cost hampers their applications in asymmetric Wittig reaction [16–25] In this context, it is highly desired to develop a catalytic version of phosphine-mediated Wittig reaction by in-situ recycling by-product phosphine oxide under the aid of a reducing agent. Silanes have been recognized as powerful reducing agents for in-situ deoxygenation of phosphine oxides with good functional tolerance after a series of successful applications of silanes in the transformation of a stoichiometric phosphine-mediated reaction into a catalytic one [46–52]. In 2009, O’Brien et al [53] developed the first catalytic Wittig reaction for efficient synthesis of alkenes in moderate to high yields by using silanes such as diphenyl silane or trimethoxysilane to reuse in-situ by-product phosphine oxide [54–56].
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