64781-39-1Relevant academic research and scientific papers
Distinction between polar and electron-transfer routes. A mechanistic study on the wittig reactions of nonstabilized ylides
Yamataka, Hiroshi,Nagareda, Katsushi,Takatsuka, Tsutomu,Ando, Katsuhiro,Hanafusa, Terukiyo,Nagase, Shigeru
, p. 8570 - 8576 (2007/10/02)
The Wittig reaction of nonstabilized ylides with benzaldehyde and benzophenone was investigated in detail by means of carbonyl-14C kinetic isotope effects, substituent effects, and isotope-scrambling and probe experiments. The reaction with benzophenone gave the carbon isotope effects and the Hammett ρ values of considerable magnitude both in Li salt-free and salt-present conditions. In contrast, they are quite small for the reaction with benzaldehyde. Enone-isomerization and dehalogenation probe experiments indicated that the nonstabilized ylide has enough ability to transfer an electron to benzaldehyde and benzophenone. These results were interpreted in a self-consistent manner by the mechanism that the Wittig reaction of nonstabilized ylides proceeds via initial electron transfer from the ylide to the carbonyl compounds. The electron-transfer step is rate-determining for benzaldehyde, while radical coupling following the electron-transfer step is rate determining for benzophenone. From the probe experiments together with the isotope effects and the substituent effects reported previously, the reaction of semistabilized ylides was concluded to proceed through a polar nucleophilic addition mechanism.
Thermal fragmentation of 3-alkyl-2-phenyloxetanes, 3,3-dimethyl-2-aryloxetanes, and related compounds. A case study of 2-aryl-substituted oxetanes
Imai, Toshiro,Nishida, Shinya
, p. 2503 - 2509 (2007/10/02)
Thermolyses of epimeric 3-alkyl-2-phenyloxetanes (1c, 1t, 2c, 2t, 3c, and 3t), 3,3-dimethyl-2-aryloxetanes (4, 5, 6, 7, and 8), 3,3,4,4-tetramethyl-2,2-diphenyloxetane (9), and 3,3-dimethyl-2,2-diphenyloxetane (10) were studied in degassed N,N,N',N'-tetramethylethylenediamine at 270-350 deg C.Although the fragmentation of 9 and 10 can be understandable on the basis of a diradical mechanism, there were several observations, in the reaction of certain other oxetanes, which could hardly be explained simply in terms of such a mechanism.Namely, (1) less strained 1t reacted faster than more strained 1c; (2) a major mode of the fragmentation for 1c, 2c, and 3c was "B" (forming an alkene and benzaldehyde), whereas that for 1t, 2t, and 3t was "A" (forming an alkenylbenzene and formaldehyde); (3) the apparent energy of activation for the "B" process seemed to be larger than that for the "A"; (4) a dramatic change of the major fragmentation mode from "B" to "A" was brought about by a substituent on the phenyl group, as was observed in 4-8.These results may be explained reasonably by assuming that the fragmentation proceeds, at least, in dual reaction courses.In competition with an anticipated diradical pathway, there will be another process, which is energetically little more favorable than the diradical fragmentation, rather specific to the "A" mode fragmentation, and important particularly in the reaction of the trans isomers.Probable candidates for the second process are discussed.
