Reactivity of Singlet and Triplet Arylnitrenes:  Temperature-Dependent Photodecomposition of 1-(2-Azidophenyl)-3,5-dimethylpyrazole

Abstract

At >200 K photolysis of 1-(2-azidophenyl)-3,5-dimethylpyrazole (5) gives 1,3-dimethylpyrazolobenzotriazole (6, by electrophilic cyclization of singlet nitrene 1 4) or, in the presence of diethylamine, aminoazepine 8 (by addition of the nucleophile and rearrangement). At lower temperatures, the yield of these products decreases and the azo derivative 9 (from the dimerization of triplet nitrene 3 4) as well as products from intramolecular radical cyclization (again via 3 4) is obtained, to become the only products at <100 K. Differential thermodynamic parameters for the reactions of 1 4 and 3 4 are determined by analysis of the temperature dependence of products distribution (ΔΔH ⧧ = −10 kJ mol-1 and ΔΔS ⧧ = 34 J mol-1 K-1 in ethanol). Addition of the amine may require previous ring enlargement to give the dehydroazepine 12; there is no indication that this is an intermediate of any stability, however, and if formed, this is in equilibrium with 1 4. Triplet nitrene 3 4 is characterized in matrix by UV spectroscopy, and its photoreactions (to give mainly intramolecular hydrogen abstraction) are separately studied.

The ability of triplet nitrenes to abstract hydrogen atoms

“…It seems that phenylnitrene derivatives mainly decay by dimerization, but there are several reports that they form aniline‐like products 10, 40. Furthermore, Albini et al 52, 53. and Schuster and Schrock54 reported that amino‐substituted phenyl derivatives also form aniline‐like products, but they suggest that these aniline derivatives are more likely to be formed via electron transfer rather than H‐atom abstraction via triplet phenyl nitrenes.…”

One-Pot Synthesis of Pyrrolo[1,2-a]quinoxaline Derivatives through Copper-Catalyzed Cascade Reactions

“…231～234 , ℃ 棕褐色固体. 1 H NMR (300 MHz, DMSO-d 6 ) δ: 9.15 (s, 1H), 9.01 (d, J＝1.5 Hz, 1H), 8.75～8.74 (m, 1H), 8.04 (d, J＝8.4 Hz, 1H), 7.94 (d, J＝8.4, 1H), 7.33～7.29 (m, 1H), 7.13～7.07 (m, 1H); 13 C NMR (75 MHz, DMSO-d 6 ) δ: 147. 6, 138.3, 129.8, 129.5, 127.3, 125.7, 117.0, 116.8, 116.1, 114.5, 112.5, 108.6. 1,3-二甲基吡咯[1,2-a]喹喔啉(3e) [7] : m.p.…”

“…1 H NMR (300 MHz, CDCl 3 ) δ: 8.63 (s, 1H), 8.12 (d, J＝7.4 Hz, 1H), 7.88 (d,J＝7.0 Hz,1H),7.52～ 7.36 (m,2H),6.39 (s,1H), 2.86 (s, 3H), 2.41 (s, 3H); 13 C NMR (75 MHz, CDCl 3 ) δ: 144.2, 137.3, 130.4, 129.7, 128.1, 126.2, 124.7, 124.4, 117.3, 116.9, 115.3, 17.6, 10.2. 1-苯基吡咯[1,2-a]喹喔啉(3f) [7] : 蜡状固体. 1 H NMR (300 MHz, CDCl 3 ) δ: 8.70 (s, 1H), 7.82 (d,J＝8.0 Hz,1H), 7.40～7.36 (m, 5H), 7.28 (d,J＝8.5 Hz,1H),7.22 (t,J＝7.7 Hz, 1H), 6.99 (t, J＝8.1 Hz, 1H), 6.83 (d, J＝4.0 Hz, 1H), 6.64 (d,J＝4.0 Hz,1H); 13 C NMR (75 MHz, CDCl 3 ) δ: 146.1, 137.2, 134.1, 132.4, 130.0, 129.8, 129.1, 128.9, 128.8, 128.7, 128.6, 127.8, 126.4, 125.0, 116.7, 116.6, 107.6. 吲哚[1,2-a]喹喔啉(3g) [7] : m.p. 111～113 , ℃ 橙色固 体.…”

“…8.42 (m, 2H), 8.00～7.96 (m, 2H), 7.61 (t, J＝7.7 Hz, 1H), 7.55 (t, J＝7.5 Hz, 1H), 7.46～7.41 (m, 2H), 7.14 (s, 1H); 13 C NMR (75 MHz, CDCl 3 ) δ: 145.2, 137. 4, 131.3, 130.2, 130.0, 129.8, 129.2, 129.0, 126.6, 126.1, 124.6, 124.4, 125.6, 115.5, 107. 7, 147.4, 135.9, 130.8, 130.4, 130.3, 130.2, 128.6, 128.0, 123.9, 115.8, 115.5, 114.5, 102.3, 100.2, 29.7 (d, J＝8.3 Hz, 1H), 8.26 (d, J＝8.3 Hz, 1H), 7.96 (d,J＝7.8 Hz,1H),7.58 (t,J＝7.8 Hz,1H),7.40 (t,J＝7.7 Hz, 1H), 7.28～7.27 (br s, 1H), 7.18～7.16 (m, 1H), 7.03 (s, 1H); 13 C NMR (75 MHz, CDCl 3 ) δ: 146.1,137.2,134.1,132.4,129.8,129.6,128.9,128.8,128.7,127.7,126.6,124.9,116.8,116.6,107.6;HRMS (EI) (d, J＝8.4 Hz, 2H), 7.09～7.04 (m, 1H), 6.96～6.94 (m, 1H); 13 C NMR (75 MHz, CDCl 3 ) δ: 159. 8, 157.4, 146.0, 135.8, 130.4, 130.3, 130.2, 128.6, 127.8, 123.9, 115.4, 114.0, 113.3, 109.2, 104.9; HRMS (EI) calcd for C 15 H 9 N 2 Cl (M＋H) ＋ 253.0543, found 253.0543.…”

“…121～123 , ℃ 白色 固体. 1 H NMR (300 MHz, CDCl 3 ) δ: 9.13 (s, 1H), 8.15～ 8.13 (m, 2H), 7.98～7.93 (m, 1H), 7.83 (s, 1H), 7.70～ 7.66 (m, 1H), 7.63～7.59 (m, 1H); 13 C NMR (75 MHz, CDCl 3 ) δ: 144. 4, 138.9, 135.9, 134.5, 130.8, 129.0, 127.4, 126.5, 114.8, 112.2.…”