Daunosamine Diels-Alder reaction

This hetero Diels-Alder reaction allows easy access to a series of pyrans with structures similar to those of the daunosamines. Thus, heating mixtures of A-acylenaminones 335 and enol ethers leads to the isomer mixture 336 and 337, Scheme 94 (86TL6181 91CB881). In all transformations, the major cis isomers 336 result from kinetic control, which is favored by low temperatures and high pressures. The thermodynamically more stable trans products 337 can be obtained by treatment of 336 with Lewis acids (88JA4065). 

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