Phenylnitrene, reaction

Singlet phenylnitrene, and hence /V,A -diethyl-3//-azcpin-2-amines, e. g. 102, can be generated by the thermolysis of A,-phenyl-Af,<9-bis(trimcthylsi]yl)hydroxylamine (100) in the presence of dialkylamines the reaction fails, however, with arylamines.210 Photofragmentation of the spiro oxaziridine 101 in diethylamine solution also produces the 3//-azepine 102,2,1 and an oxaziridine intermediate is probably involved in the formation, in low yield (1 %), of azepine 102 by the photolysis of A/,A( -diarylbenzoquinonc diimine A/,A/ -dioxides in benzene/die-thylamine solution.212... 

DIFFERENCES BETWEEN PHENYLCARBENE AND PHENYLNITRENE AND THE RING EXPANSION REACTIONS THEY UNDERGO... 

In this chapter we describe experimental studies on the ring expansion reactions of phenylcarbene and phenylnitrene and the calculations that have been performed in order to try to explain the experimental results. Our aim is to show how theory can rationalize these observations and can also serve to stimulate additional experiments by predicting their outcome. We will attempt to demonstrate that an understanding of the fundamental differences between the electronic structures of phenylcarbene and phenylnitrene can explain the many differences in the chemistry of these reactive intermediates. 

Before discussing recent studies on the ring expansion reactions of phenylcarbene and phenylnitrene, we will describe some of the earlier experimental and theoretical work on these molecules. Our purpose here is to give a brief overview, in order to provide a context for the discussion of more recent results. For detailed descriptions of the chemistry of arylcarbenes and arylnitrenes, we refer the reader to the many excellent reviews in this area.1,2... 

The apparent absence of large electronic effects on the cyclization reactions of derivatives of phenylnitrene has been attributed to the nature of the wave function for the lowest singlet state, which, as discussed earlier, resembles a... 

In order to test the validity of these qualitative expectations, CASPT2/6-31G calculations on the ring expansion reactions of ortho, meta, and para-cyano-phenylnitrene (12a-c) were performed.96 Fig. 15 summarizes the results. In all three cases, the ring expansions were computed to be nearly thermoneutral, with the first step rate-determining. 

By furnishing both explanations and predictions, calculations have not only led to an understanding of experiments that have already been performed on la and lb, but also have motivated new ones. The study of the chemistry of phenylcarbene (la) and phenylnitrene (lb), particularly the ring expansion reaction that each undergoes, thus provides an excellent example of the synergy between calculations and experiments. 

Kinetic and mechanistic studies of the reactivity Zn-Oh ( = 1 or 2) species in small molecule analogs of zinc-containing metalloenzymes, 41, 81 Kinetics and spectroscopy of substituted phenylnitrenes, 36, 255 Kinetics, of organic reactions in water and aqueous mixtures, 14, 203 Kinetics, reaction, polarography and, 5, 1... 

Partitioning of carbocations between addition of nucleophiles and deprotonation, 35, 67 Perchloro-organic chemistry structure, spectroscopy and reaction pathways, 25, 267 Permutations isomerization of pentavalent phosphorus compounds, 9, 25 Phase-transfer catalysis by quaternary ammonium salts, 15, 267 Phenylnitrenes, Kinetics and spectroscopy of substituted, 36, 255 Phosphate esters, mechanism and catalysis of nucleophilic substitution in, 25, 99 Phosphorus compounds, pentavalent, turnstile rearrangement and pseudoration in permutational isomerization, 9, 25 Photochemistry, of aryl halides and related compounds, 20, 191 Photochemistry, of carbonium ions, 9, 129... 

With the purpose of understanding the crosslinking mechanism of 1,2-polybutadiene with aromatic nitrene, we studied the reaction of phenylnitrene with unsaturated olefine monomers such as 3-methyl-1-butene and cyclohexene. These monomers are structually similar to a unit segment of 1,2-polybutadiene. 

Formation of aziridine by direct reaction of phenylnitrene with 3-methyl-1-butene... 

When, phenylazide and 3-methyl-1-butene are mixed in benzene and kept standing for a couple of days, triazoline is formed and it gives aziridine by thermal or photodecomposition. However, when the mixture is irradiated as soon as they are mixed, the aziridine which is found in the solution is the one formed, not by the decomposition of the triazoline but, by direct photochemical reaction of phenylnitrene with 3-methy1-1-butene. 

The structure of each compound isolated by the above method was determined by comparing its spectra with those of corresponding compound synthesized by the known method. Furthermore, the retention time of the gas chromatogram was compared with those of the known compounds. The following products were obtained from direct reaction of phenylnitrene with cyclohexene aniline[8](determined by electronic spectrum, gas chromatography), 7-phenyl-7-azabicyclo[U,l,0]heptane[9](determined by electronic, IR, Mass and NMR spectrum), N-(3-cyclohexenyl)aniline[l0](determined by electronic, IR, Mass and NMR spectrum) and 3,3 -bicyclohexenyl[ll] (determined by IR, Mass and NMR spectrum). 

Quantitative determination of the reaction products of phenylnitrene with cyclohexene... 

The dimerization of phenylnitrene to form azobenzene is a characteristic reaction of the triplet state of an arylnitrene. Thus, some intermediate formed along the reaction coordinate must undergo intersystem crossing to the triplet manifold. 

For example, the ring expansion reactions undergone by phenylnitrene and phenylcarbene manifested themselves for the first time by conspicuous IR bands at 1895 or 1815 cm that were observed after photolysis of matrix-isolated phenyl... 

Secondly, Leyva et al found that the solution phase photochemistry of phenylazide (PA) was temperature dependent. Photolysis of PA in the presence of diethylamine at ambient temperature yields azepine 2, first prepared by Doering and Odum. Lowering the temperature suppresses the yield of 2 and encomages the formation of azo compound. Thus, high temperatures favor reactions of singlet state intermediates, whilst low temperatures favor reactions associated with triplet phenylnitrene. 

Table 7 (8/8)CASSCF and CASPT2/6-31G energies (kcal/mol), relative to the reactants, for the transition structures and products in the cyclization reactions of singlet phenylnitrene and of the ortho-, meta-, para-, and 2,6-dicyano derivatives. ...

Fig. 13 Arrhenius treatment of A r(= qbs isc) for singlet pora-fluoro- 16b (1), meto,meto-difluorophenylnitrene 16c (2) in pentane and ortho,onho-Ai uoro-phenylnitrene 16d (4) in CCI4 and for singlet 2-fluorophenylnitrene 16a (3) calculated as described in the text. (5) Arrhenius treatment of the rate constant of ring opening reaction (k ) for benzazirine 17a.

KINETICS OF BIMOLECULAR REACTIONS OF FLUORO-SUBSTITUTED PHENYLNITRENES... 

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