Synthesis of a stereochemically defined 1,2-diazetine N,N′-dioxide and a study of its thermal decomposition

Article abstract of DOI:10.1021/jo062357c

(Chemical Equation Presented) Diazetine dioxide 1a has been synthesized in a single step via oxidation of meio-2,3-diphenyl-1,2-ethanediamine with dimethyldioxirane, albeit in low yield (7%). Thermal decomposition of 1a afforded predominantly either trans-stilbene or diphenyl glyoxime depending on solvent, temperature, and the presence of an amine catalyst. Reaction in chloroform at 69°C favored elimination of NO and formation of trans-stilbene. The stereospecific formation of trans-stilbene suggests a mechanism of decomposition in which C-N bond cleavage leads to a diradical intermediate stabilized by the phenyl group. Bond rotation followed by cleavage of the second C-N bond accounts for the trans-stilbene. At 25 °C in chloroform, while trans-stilbene was still the major product, some diphenyl glyoxime was also observed (4% yield). However, la as a solution in chloroform in the presence of Et₃N, or 1a as a solution in DMSO-d₆, afforded predominantly diphenyl glyoxime. These results are interpreted in terms of two closely competing reactions subject to the effects of entropic contributions.