Syntheses of Amino‐dideoxyallose and Amino‐deoxyribose Derivatives Using Acylnitroso Dienophiles

The dimethyl acetals 4 of (E) ‐2,4‐pentadienal and of ( E , E )‐ and ( E , Z )‐2,4‐hexadienals undergo regio‐ and stereospecific cycloaddition reactions with in ‐ situ ‐generated acylnitroso dienophiles 5a and 5b , leading thereby to the corresponding dihydrooxazines 7a–d and 8c–d . cis ‐Glycolization of these latter adducts stereospecifically gave the dihydro derivatives 9a–d and 10d which, after sequential hydrogenolysis, deacetalization, and instant cyclization, led to the aminodeoxyribose derivatives 17a, 17f , and 18 , and to the amino‐dideoxyallose compounds 17c and 17h . These piperidino‐deoxysugar derivatives exhibit a strong anomeric effect, i.e. OHC(1) is always axial, which is explained in terms of a n N (π)‐σ*(COH) orbital compression, as compared to the less pronounced one in the more classical pyranose series.