Abstract 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 ...
