Synthesis of Furans – Recent Advances.

Furans constitute an important class of aromatic heterocycles displaying a wide range of pharmacological activities.[[1]] In addition, furans are the chief motifs of many natural products.[[7]] Furans are used as flavor and fragrance compounds as well. A mild gold catalyzed cascade reaction of cyclopropanes derived from enones led to the synthesis of highly substituted furans ( I Scheme 17 i ).[63] Mechanistically furan formation takes place through the attack of a carbonyl oxygen lone pair on the alkyne followed by rearrangement. Early on, D'yakonov and Komendantov used this strategy to obtain 2-alkoxy furans using Cu(II) species.[[82]] Later, numerous research groups expanded this reaction by using different transition metal catalysts for the efficient synthesis of furan molecules. The Ph SB 3 sb PO produced by the Wittig reaction of phosphorane B 146 b and 1,2-dicarbonyl compound B 147 b is used to catalyze the 1,4-reduction of enone intermediate in the presence of HSiCl SB 3 sb and the waste HCl thus generated promotes the cyclization reaction to yield the final furan product ( I Scheme 51 i ).[113] The appearance of so many new papers on furan synthesis periodically is a testimony to the importance and relevance of the heterocycle.[[138]] This review highlights a variety of synthetic methodologies adopted for furan synthesis and focuses on the literature from 2005 onwards. [Extracted from the article]