Hetero-Diels-Alder Reaction Of Substituted 1-Oxabutadienes And 2-Ethoxyvinylacetate. An Entry To Various Natural Occurring Carbohydrates

Article abstract of DOI:10.1016/S0040-4039(00)88857-7

The hetero-Diels-Alder reaction of 1-oxabutadienes 1a-e bearing an electron-withdrawing group at C-2 or C-3 with (E)- and (Z)-2-ethoxyvinylacetate (2a and 2b) yields the highly functionalized 3,4-dihydro-2H-pyrans 3a-h and 4a-h in mostly excellent yield and modest to good endo/exo selectivity.The cycloadducts 3a and 3c are easily transformed by stereoselective hydrogenation to the ezoaminuroic acid and desosamine derivatives 5 and 7, respectively.The phthalimido-protecting group in 5 and 7 can be removed by reductive cleavage to give 6 and 8.Transformation of 4f by chloro hydrogen exchange affords the corresponding dichloro- as well as the monochloro-compound.