Hetero-diels-alder reaction of enaminecarbaldehydes an entry to branched aminosugars

N-acyl-enaminecarbaldehydes 6a - g with an electron accepting group in the α- position react in a hetero-Diels-Alder cycloaddition with enolethers 7a - g to 4-amino- dihydropyrans 8a - g, 9a - g and 10a - g. This reaction represents a convenient entry to branched aminosugars of the garosamine-type. The rate of the cycloaddition depends strongly on the N-acyl group in 6. However, the phthalimide 11 does not react because of deconjugation of the electron accepting function in the α-opposition.