SPIRO-FUSED 2-ALKOXY-2-AMINO-DELTA(3)-1,3,4-OXADIAZOLINES - SYNTHESISAND THERMOLYSIS TO CORRESPONDING AMINOOXYCARBENES

Delta(3)-1,3,4-Oxadiazolines spiro-fused at C2 to C2 to oxazolidines ( 12) or to C2 of tetrahydro-1,3-oxazines (13) were synthesized. The oxa diazolines undergo thermolysis in benzene at 90 degrees C with first-o rder rate constants of (1.6-50) x 10(-5) s(-1). The dependence of thes e rate constants on the nature of the substituents present on the oxad iazoline ring is consistent with a mechanism involving a carbonyl ylid e intermediate. Substituents on N of the oxazolidine or tetrahydro-1,3 -oxazine moieties play a major role in determining the fragmentation p athways. Oxadiazolines with N-carbonyl groups (12c-j, 13d,e) afford es sentially quantitative yields of the corresponding aminooxycarbenes, w hile other fragmentation reactions compete with carbene generation in the case of oxadiazolines with N-methyl (12b, 13c) or N-sulfonyl (12k) groups.