Diversity oriented synthesis of fused-ring 1,3-oxazines from carbohydrates as biorenewable feedstocks

Microwave enhanced diversity oriented synthesis (MEDOS) of various N- and O-heterocyclic systems fused with 1,3-oxazine ring is reported. The synthesis represents a new montmorillonite K-10 clay-catalyzed green protocol, which utilizes d-glucose/d-xylose as biorenewable feedstocks. d-Glucose/d-xylose-derived 1,3-oxazin-2-ones(thiones) either directly undergo K-10 clay-catalyzed cyclization to yield pyrano-/furo-1,3-oxazine systems under solvent-free microwave irradiation conditions or afford azolo-/azino-1,3-oxazines when subjected to Malaprade reaction followed by cyclization with appropriate reagents, viz. phenylhydrazine, hydroxylamine, acetamidine, phenylurea and semi(thiosemi)carbazide.