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An excellent catalyst DABCO has been found to catalyze C-C bond formation reaction between activated methylenes and alkynes. The transformation has provided a facile route for the synthesis of 2H-pyran-2-ones or unsaturated alkenoic acid ester derivatives

Acetais like 3,3-dlethoxyproplonate bearing electron-withdrawing groups were found to undergo cyclodimerization and cyclotrimerization in the presence of Lewis acids to give coumalates and 1,3,5-trisubstituted benzenes. The selectivity of these products depended on the Lewis acids employed. For instance, ethyl coumalate was obtained from, ethyl 3,3diethoxypropionate in high selectivity under the influence of d-block Lewis acids like FeCl3, whereas triethyl 1,3,5-benzenetricarboxylate was obtained in preference to ethyl coumalate under the influence of lanthanoid Lewis acids like GdCl3, Various coumalates were synthesized by the FeCl3catalyzed cross-cyclodimerization of acetals with active methylene compounds, From 4,4-diniethoxy-2-butanone, however, 1,3,5-triacetylbenzene, which is difficult to prepare regioselectively by conventional methods, was formed in quantitative yield under the influence of AlCl3, This reaction would provide a very convenient route to 1,3,5-triacetylbenzene,

Base catalysed glutaconate-pyrone systems involved in the formation of xanthyrones and glaucyrones also produce benzenoid and naphthalenoid compounds dependent on the system and conditions involved. "Dimer" type condensations usually require milder base than the "monomeric" type and three base-catalysed cases are encountered involving: (a) two aldol and one Claisen condensations; (b) three aldols; and (c) Michael addition and lactonisation.An example of Lewis acid catalysed formation of a coumarin from dimethyl 2,4-dimethoxycarbonyl glutaconic ester is also given.Arationale is suggested for the formation of trimethyl methyltrimesate in a "melt" reaction, and of the products from the treatment of certain xanthyrones with sodium methoxide.