SYNTHESIS OF SPIRO-SUBSTITUTED 1,3-OXAZINES BY A NEW SEQUENCE LEADING TO SPIROHETEROCYCLES

The target compounds, i.e. 1,3-oxazines which are spiro-substituted in position 6 by a piperidine moiety, are derived from 1-oxa-3,9-diaza-spiro [5.5]undecane, a novel heterocyclic parent system. They were all approached by the following three-step sequence: 1,3-dipolar cycloadditions of nitrile oxides and nitrones to piperidines bearing an exocyclic methylene group gave the corresponding spiro-substituted oxazole derivatives 3. In a consecutive step these were cleaved by hydrogenolysis to gamma-amino-alcohols 4, which in a final step were recyclized by insertions of a C-1-unit to yield the target structures 5-10: thus a de facto ring-extension of spiro-oxazoles to spiro-oxazines was accomplished.