Wangyong Huang, Yi-Chieh Chen, Kwunmin Chen
Apr 1, 2012
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0
Influential Citations
67
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Journal
Chemistry, an Asian journal
Abstract
Furans represent an important subclass of five-membered aromatic heterocycle that has been used for the synthesis of many pharmaceutical molecules and industrial materials. The functionalization of furans often allows for further structural elaboration and adornment. As a consequence, many valuable synthetic protocols have been devised for the construction of polysubstituted furans, and these are based either on introducing substituents onto the existing furan ring or furan ring construction from acyclic precursors. Derivatization of furans often requires the application of a metal–halogen exchange reaction or a transition-metal-catalyzed cross-coupling, with the halide precursor emanating from an electrophilic substitution process. On the other hand, some excellent methods have been developed for the build-up of functionalized furans from acyclic precursors, some of which utilize alkynyl epoxides, a-alkenyl-bdiketones, cyclopropenyl ketones, g-acyloxy butynoates, alkynyl ketones, b-acyloxy acetylenic ketones, aalkynyl enones, thioalkynone, alkynol/alkyne, alkynoate/1,3-dicarbonyls, propargylic alcohols/1,3-dicarbonyls, propargylic alcohols/ketones, allenyl ketones, propargylic esters, propargyl vinyl ethers, alkynyl cyclopropyl ketones, alkenyl carbene/enones, b-alkynyl enals, acyloxy sulfones, enynols, and various other substrates. The application of these methods often requires the preparation of specially tailored starting substrates utilizing transition-metal catalyzed reactions. The Paal–Knorr reaction has proven particularly useful for furan ring assembly. The reaction of 1,3-dicarbonyl compounds with a-haloketones (the Feist–B nary reaction) under metal-free conditions, is another longstanding historical protocol that has provided rapid access to many different types of substituted furans. The development of facile new methods for the efficient ring assembly of tetrasubstituted furans remains a highly desirable and challenging objective for many in the field. We present herein a unique and generally efficient synthetic strategy for accessing tetrasubstituted furans that exploits a Feist–B nary type reaction between electron-deficient nitroallylic acetates 1 and 1,3-dicarbonyl/a-activating ketones. The corresponding multifunctional 3,5-alkyl/aryl-2-carboxylate-4-keto/cyano-containing tetrasubstituted furans were typically obtained in respectable to excellent yield (52– 99 %) via an interesting SN2 addition–elimination sequence that proceeds under very mild reaction conditions [Eq. (1)].