[3]-1-Azadendralenes as Versatile Building Blocks for the Stereoselective Synthesis of Polysubstituted Hexahydroquinazolin-2-ones and Hexahydrobenzothiazine-2-­imines.

A diene-transmissive hetero-Diels-Alder reaction of cross-conjugated 1-azatrienes (-1-azadendralenes) is described for the synthesis of hexahydroquinazolin-2-ones and hexahydrobenzothiazine-2-imines derivatives. [4+2] Cycloaddition reactions with tosyl isocyanate or aryl isothiocyanates gave mono-cycloadducts with high chemo- and regioselectivities. The second Diels-Alder reaction with representative dienophiles, tetracyanoethylene, N-phenylmaleimide, and methyl vinyl ketone, stereoselectively produced ring-fused nitrogen heterocycles. Skeletal diversity can be accessed by combining the three reaction partners - primary amine, tosyl isocyanate, and cross-conjugated 1-oxatriene - in a different sequential order. [ABSTRACT FROM AUTHOR]