Following numerous applications of Wittig reaction now functionalized phosphonium
salts are gaining attention due to their characteristic properties and diverse reactivity.
This review is focused on α-alkoxyalkyl triphenylphosphonium salts: an important
class of functionalized phosphonium salts. Alkoxymethyltriphenylphosphonium salts are
majorly employed in the carbon homologation of carbonyl compounds and preparation of
enol ethers. Their methylene insertion strategy is extensively demonstrated in the total
synthesis of a wide range of natural products and other important organic molecules. Similarly
enol ethers prepared thereof are important precursors for different organic transformations
like Diels-Alder reaction, Claisen rearrangement, Coupling reactions, Olefin metathesis
and Nazarov cyclization. Reactivity of these α-alkoxyalkylphosphonium salts
have also been studied in the nucleophilic substitution reactions. A distinctive application of this class of phosphonium
salts was recently reported in the phenylation of carbonyl compounds under very mild conditions.
Synthesis of structurally diverse alkoxymethyltriphenylphosphonium salts with variation in alkoxy groups as
well as counter anions are reported in literature. Here we present a detailed account of different synthetic
methodologies for the preparation of this unique class of quaternary phosphonium salts and their applications
in organic synthesis.
Keywords: Quaternary phosphonium salts, functionalized phosphonium salts, methoxymethyl triphenylphosphonium chloride, carbon homologation,
vinyl ethers, enol ethers, nucleophilic phenylation.
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