Comprehensive reinvestigation of the reaction of D-aldoses with Meldrum's acid yielding mainly chain extended 3,6-anhydro-2-deoxy-aldono-1,4-lactones

All diastereomeric aldo-D-pentoses and -D-hexoses were reacted with Meldrum 's acid (2,2-dimethyl-1,3-dioxane-4,6-dione) under basic conditions. A prot ocol was applied and optimized which was originally reported by J. A. Galbi s Perez et al. in 1990. In every case formal substitution of the anomeric h ydroxyl against a carboxy-methylene group occurred thus elongating the carb on chain of the parent aldose by a C-2 fragment. Products are mainly 3,6-an hydro-2-deoxy-aldono-1,4-lactones in which the lactone rings are annulated to a furanoid system. However, D-mannose and D-lyxose also gave pyranoid 3, 7-anhydro-1,4-lactones. Intermediates are unsaturated open-chain 1,4-lacton es (butenolides) which in some cases could be isolated as by-products. Epim erisation at C-2 of the parent aldose occurred at least partially in most r eactions. The products and their acetylated derivatives were characterized by H-1 and C-13 NMR spectroscopy. A proposed mechanism of this reaction is supported by additional experimental evidence.