Acetylenedicarboxylic esters with 2-pyridones

The cycloaddition chemistry of pyridones (695) is quite analogous to that of the a-pyrones (79CC1091). Pyridones will react under high pressure conditions with acetylenedicarboxylic acid esters to furnish cycloadducts (696) which when heated expel a molecule of an isocyanate to yield substituted aromatics (697 Scheme 163). 

CR(Q(262)1017>. The nucleophilic reactivity of the oxygen atom has been observed in the acetylation by acetic anhydride of 2-aryl- and 2-heteryl-A2-thiazolin-4-ones (Scheme 136). 2-Alkoxy and 2-methyl derivatives of A2-thiazolin-4-one (196) react with OPCl3 to yield thiazolylphosphoric esters (197) which have insecticidal uses (Scheme 137). An example of the electrophilic reactivity of the C-4 atom is the easy formation of oxime and phenylhydrazone derivatives. 5-Aryl-A2-thiazolin-4-one (198) gives the 1,3-dipolar cycloaddition product (199) with methyl fumarate and methyl maleate (Scheme 138). Under similar conditions, treatment of (198) with dimethyl acetylenedicarboxylate (DMAD) yields a thiophene derivative (202) when R = Ph and a pyridone derivative (203) when R = H (Scheme 139). The proposed mechanism involves the formation of a mesoionic intermediate (200) which reacts in a cycloaddition with a second molecule of DMAD, yielding (201), the decomposition of which depends on the R substituent. 

Addition of diethyl phosphite to ethyl propiolate or 3-substituted ethyl propiolates under basic conditions produces a mixture of mono- and bisphosphonyl esters. When p-enaminophospho-nates are allowed to react with an equimolecular amount of dialkyl acetylenedicarboxylate in THF at 50°C, substituted 2(l//)-pyridones containing phosphoryl and alkoxycarbonyl groups attached to the ring are obtained. ... 

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