Application of 2,4,6-trioxo-pyrimidin-5-ylidene alditols in the synthesis of pyrano[2,3-d]pyrimidines containing a sugar moiety by hetero-Diels–Alder reactions and by conjugate Michael addition–cyclizations

A convenient and efficient procedure for the preparation of 3,4-dihydro-2H-pyran derivatives containing a sugar moiety is described. The reaction sequence is: Knoevenagel condensation of unprotected sugars and CH acids, acetylation of C-glycosides and hetero-Diels–Alder reaction. O-Acetylated 1,3-dimethyl-2,4,6-trioxo-pyrimidin-5-ylidene derivatives were used as new heterodienes in the synthesis of fused uracils—pyrano[2,3-d]pyrimidines with a sugar moiety. Solvent-free hetero-Diels–Alder cycloadditions of O-acetylated pyrimidin-5-ylidene alditols with enol ethers and cyclic enol ether were investigated at room temperature. New, enantiomerically pure cis and trans diastereoisomers of pyrano[2,3-d]pyrimidines and cis–cis, trans–cis diastereoisomers of pyrano[3′,2′:5,6]pyrano[2,3-d]pyrimidines with alditol moiety were obtained. The same pyrimidin-5-ylidene alditols underwent conjugate Michael addition–cyclizations with malononitrile at room temperature to afford optically active diastereoisomers of pyrano[2,3-d]pyrimidine-6-carbonitriles with a sugar moiety.