Synthesis and thermolysis of a spiro-fused oxadiazoline — Evidence for sequential formation of carbene and oxirane intermediates, and for oxirane dimerization

The spiro-fused oxadiazoline, 3,4-diaza-2,2-dimethyl-1,6,10-trioxaspiro[4.5]dec-3-ene, when thermolysed in a sealed tube in benzene-d 6 at 110 °C, afforded acetone and an apparent oxirane intermediate (2,2-dimethyl-1,4,8-trioxaspiro[2.5]octane) that could not be isolated. Attempts to isolate the oxirane gave a dimer (8,8,11,11-tetramethyl-1,5,7,10,12,16-hexaoxadispiro[5.2.5.2]hexadecane) as the major product. The oxirane is thermally stable at …