Butenolides and Tetronic Acids

Butenolides and Tetronic Acids.—A number of routes to halogenated butenolides have been reported. Larock and Riefling have described a promising method for the carbonylation of the vinyl chloromercury derivatives (60) of primary and tertiary acetylenic alcohols which produces 3-chlorobutenolide (61) in high yield. 

Drieding has studied a number of ways to prepare bromobutenolides. Acid-catalysed cyclizations of 3-phenylallenecarboxylic acids (62) have been found  

Spirobutenolides (66) have been prepared from the carbanion of 3-phenyl-sulphinylpropionic acid (65) by condensation with cyclopentanone followed by desulphurization. 

Ylidenebutenolides (67) and (68), although rather labile, have been obtained in good yields by coupling morpholine enamines with ketomalonate followed by cyclization of the resulting carbinols. The more reactive pyrrolidine derivatives lead to cyclopentanedione derivatives instead. A further application of 4-phos-phoranylidenebutenolide (69) to the synthesis of ylidenebutenolides has been reported.  

A route to 3-alkyl butenolides, starting from 4,4-diethoxyacetoacetate, has been outlined,  

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This review of furan chemistry is meant to continue the earlier survey by Bosshard and Eugster1 and concentrates upon the period 1968 to the end of 1979. Like the earlier review, this one is limited to the chemistry of the monocyclic furan nucleus and does not deal, except incidentally, with fused rings such as benzofuran or its quinones. Nor does it deal in detail with dihydro- or tetrahydrofurans, nor with compounds like furylpyridine that contain some other heterocyclic nucleus as well. Some butenolides and tetronic acids are admitted to consideration since they are the carbonyl equivalents of hydroxyfurans regarded as enols, but side-chain reactions are wholly excluded unless the furan nucleus clearly affects them in some important way. 

Butenolides and Tetronic Acids.—An alternative method for the preparation of but-2-en-4-olide itself, in 62—71% yield, from furan employs a mixture of bromine, acetic acid, acetic anhydride, and sodium acetate. ... 

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