Methyl 3 -furanone-2-carboxylate

CYCLOADDITION Alumina chloride. l,2-Bis(trimethylsilyloxy)cyclo-butene. 2,2-Dimcthyl-3(2//)-furanone. Lthylaluminum dichloridc. Kctcnc diethyl acetal.. Methyl cyclobutene-carboxylate. Trimethyl-1,3-dioxolen-one. Zinc chloride. 

Labeling experiments with l-deoxy-l-(dibenzylamino)-D-[l- C]-aruI>-mo-2-hexulosuronic acid [l- C] 112 indicated that the C label corresponded to the 5-methyl group of 111 (see Ref. 234). This is also consistent with a l-deoxy-2,3-dicarbonyl intermediate (115), and indicates that 111 is a decarboxylation product (see Scheme 22). The precise step entailing decarboxylation has not yet been determined. The carboxyl group could be carried through to ring closure (furanone formation). Such a step would provide a 2-carboxylate which is a /3-keto acid subject to ready decarboxylation. The labeling information and the initial steps of the mechanism in Scheme 22 are also consistent with the formation of 111 from D-[l- C]ribose and a secondary amine. ... 

Wamhoff and Huang obtained alkyl 2,3,4,9-tetrahydro-6-oxo-67/-pyrido[l,2-a]pyrimidine-9-carboxylates 237 in the reaction of 3-(hexahy-dropyrimidin-2-ylidene)-2(3.//)-furanones 235 (R3 = H) and methyl propi-olate in a refluxing alcohol in excellent yields (Scheme 17) (84CB1856). When the reactions were carried out in benzene or dioxane, addition products 236 could be isolated, which then were transformed in quantitative yields to tetrahydro-6-oxo-6//-pyrido[ 1,2-a ]pyrimidine-9-carboxyl-ates 237 by stirring in an alcohol at ambient or elevated temperature. When 3-(hexahydropyrimidin-2-ylidene)-2(3//)-furanones 235 (R3 = Me) were reacted with methyl acrylate or with dimethyl acetylenedicarboxy-late, hexahydro- and tetrahydropyridopyrimidin-6-ones 238 and 239, respectively, were obtained in good yields (84CB1926). 

Thus, a biosynthetic pathway was proposed starting with enolate formation of one phenylpyruvate molecule followed by aldol-like condensation and cyclization to give the carboxylated furanone moiety. Decarboxylation in X. szentirmaii results in the formation of 53, which is methylated in a SAM-dependent mechanism to give 54 as final product [262],... 

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