A synthetic entry into fused pyran derivatives through carbon transfer reactions of 1, 3-oxazinanes and oxazolidines with carbon nucleophiles

Abstract

Acid catalysed condensations of various 2 substituted 1,3-oxazinanes 3 and 1,3-oxazolidines 4 with cyclic carbon nucleophiles viz. 5,5-dimethyl-1,3-cyclohexanedione and 1,3-cyclohexanedione furnish xanthene derivatives, whereas a Knoevenagel reaction proceeds with acyclic nucleophiles. In case of 4b and 4c, a unique synthesis of functionalised α-tetralones has emerged. Reactions of mixtures of cyclic and acyclic carbon nucleophiles with 3 provide some functionalised and partially reduced benzopyran derivatives.