Base-Mediated Fragmentation of Bicyclic Dihydro-3,6-oxazines: Transformation of Nitroso Diels-Alder Cycloadducts.

Nitroso Diels-Alder cycloadditions of benzene oxide with various acyl-nitroso derivatives are described. Treatment of these cycloadducts with methyllithium results in a fast fragmentation reaction, leading to highly functionalized cyclic amino alcohols. The mechanism of the reaction and the role of the epoxide in the fragmentation process are investigated. The reaction proceeds via the formation of an unsaturated imine, which tautomerizes to an enamine if no neighboring epoxide is present.