Synthesis of a Stereochemically Defined 1,2-Diazetine N,N'-Dioxide and a Study of Its Thermal Decomposition

摘要

Diazetine dioxide 1a has been synthesized in a single step via oxidation of meso-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℃ 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℃ in chloroform, while trans-stilbene was still the major product, some diphenyl glyoxime was also observed (4% yield). However, 1a as a solution in chloroform in the presence of Et_3N, or 1a as a solution in DMSO-d_6, afforded predominantly diphenyl glyoxime. These results are interpreted in terms of two closely competing reactions subject to the effects of entropic contributions.