Nitrile Imines and Nitrile Ylides: Rearrangements of BenzonitrileN-Methylimine and Benzonitrile Dimethylmethylide to Azabutadienes, Carbodiimides, and Ketenimines. Chemical Activation in Thermolysis of Azirenes, Tetrazoles, Oxazolones, Isoxazolones, and Oxadiazolones

Abstract

Flash vacuum thermolysis (FVT) of 1-methyl-5-phenyltetrazole (5b), 2-methyl-5-phenyltetrazole (1b), and 3-methyl-5-phenyl-1,3,4-oxadiazol-2(3H)-one (3b) affords the nitrile imine (2b), which rearranges in part to N-methyl-N'-phenylcarbodiimide (7b). Another part of 2b undergoes a 1,4-H shift to the diazabutadiene (13). 13 undergoes two chemically activated decompositions, to benzonitrile and CH2═NH and to styrene and N2. FVT of 2,2-dimethyl-4-phenyl-oxazol-5(2H)-one (16) at 400 °C yields 3-methyl-1-phenyl-2-azabutadiene (18) in high yield. In contrast, FVT of 3,3-dimethyl-2-phenyl-1-azirene (21) at 600 °C or 4,4-dimethyl-3-phenyl-isoxazolone (20) at 600 °C affords only a low yield of azabutadiene (18) due to chemically activated decomposition of 18 to styrene and acetonitrile. There are two reaction paths from azirene (21): one (path a) leading to nitrile ylide (17) and the major products styrene and acetonitrile and the other (path b) leading to the vinylnitrene (22) and ketenimine (23). The nitrile ylide PhC(-)═N(+)═C(CH3)2 (17) is implicated as the immediate precursor of azabutadiene (18). FVT of either 3-phenylisoxazol-5(4H)one (25) or 2-phenylazirene (26) at 600 °C affords N-phenylketenimine (28). The nitrile ylide PhC(-)═N(+)═CH2 (30) is postulated as a reversibly formed intermediate. N-Phenylketenimine (28) undergoes chemically activated free radical rearrangement to benzyl cyanide. The mechanistic interpretations are supported by calculations of the energies of key intermediates and transition states.

Photoinduced reactions of both 2-formyl-2H-azirine and isoxazole: A theoretical study based on electronic structure calculations and nonadiabatic dynamics simulations

“…Similar activation energies for the rearrangement to azirines from nitrile ylides were also reported by Wentrup and coworkers. 96 To investigate the photodynamics, 100 trajectories were calculated starting from the Franck-Condon geometry of the S 2 state of 2-formyl-2H-azirine. The C 4 -O 5 and C 2 -C 3 distances as a function of simulation time for the calculated trajectories were plotted in Figures 3(c) and 3(d), respectively.…”

“…6.5 kcal mol −1 , whereas the corresponding rearrangement to ketenimine would require 33.4 kcal mol −1 . 96 To investigate the photodynamics, 100 trajectories were calculated starting from the Franck-Condon geometry of the S 1 state. There are seven trajectories which fail due to the CASSCF convergence problem.…”

“…The rearrangement to ketenimines from vinylnitrenes in the singlet state was reported to require a barrier of 33.3 kcal mol −1 . 96,102 Alternatively, the 1,2hydrogen shift reaction can occur barrierlessly through the initial population of the S 2 state of β-formylvinylnitrene. Analysis of the calculated CASSCF wavefunctions and electron occupation of electronic states involving in the S 2 decay of β-formylvinylnitrene demonstrates that the closeshell state of vinylnitrene mediates the 1,2-hydrogen shift reaction.…”

Pyrolysis of hydrazine derivatives and related compounds with N N single bonds

“…The dialkylamino radicals, formed either thermally or photochemically in solution, can be used as initiators for radical polymerization [177] The reaction of the dimethylamino radical with toluene and substituted toluenes yielded a Hammett value of -1.08 for the abstraction reaction giving R 2 NH and a deuterium isotope effect of 4.0. The rate of the thermal decomposition of tetramethyl-2-tetrazene (TMT) in benzene solution at [126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141][142] o C were of the order 10 -5 -10 -4 s -1 with an approximate energy of activation of 45 kcal/mol -rather high compared with the gas-phase values given above. Importantly, however, at concentrations of TMT greater than 0.2 M, induced decomposition of the tetrazene becomes important [178].…”

Falling‐Solid Flash Vacuum Pyrolysis: An Efficient Preparation of Arylacetylenes

“…[2] Thes ynthesis of the p-nitrobenzylidene isoxazolone 9 took an unexpected course.Infact, the product of reaction of 3-methylisoxazolone (4)w ith p-nitrobenzaldehyde was the bis(isoxazolyl)methane derivative 8,which is far too involatile for conventional FVP.However,falling-solid pyrolysis of 8 at 750 8 8Ca fforded 10 in 71 %y ield (Scheme 2). During the course of this reaction 3-methylisoxazolone (4)iseliminated, thus generating 9,which subsequently undergoes pyrolysis to form 10.T he eliminated 3-methylisoxazolone undergoes pyrolysis to form 2-methyl-1-azirine,a sw eh ave described for the analogous formation of 2-phenyl-1-azirine, [10] but under these reaction conditions the azirine decomposes to form HCN and ethene.…”