Metal‐free ring opening of 5‐amino‐1,4‐diaryl‐1H‐pyrazoles: A facile access to 2‐aryl‐3‐arylazoacrylonitriles

Abstract

Various 2‐aryl‐3‐arylazoacrylonitriles are synthesized while attempting the intramolecular N‐arylation of 5‐aminopyrazoles, using the hypervalent iodine reagent. The synthesis involves phenyl iodine diacetate‐assisted ring opening of 5‐aminopyrazoles at room temperature. A plausible mechanism for the formation of azoalkenes is proposed.

Organocatalytic Dearomatization of 5-Aminopyrazoles: Synthesis of 4-Hydroxypyrazolines

“…5-Amino-3-methyl-1,4-diphenyl-1H-pyrazole (4a). 27 Reaction time 3 h; yield 99% (0.616 g); brown solid; R f = 0.24 in 20% EtOAc in n-hexane; mp 165−167 °C; IR (KBr, ν, cm −1 ) 3421, 1627,1559,1506,1454,1390,1023,758; 1 H NMR (400 MHz, CDCl 3 ) δ 7.61 (d, J = 8.0 Hz, 2H), 7.50−7.43 (m, 4H), 7.38−7.27 (m, 4H), 3.95 (s, 2H), 2.32 (s, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ) δ 147. 3, 142.2, 138.6, 133.4, 129.6, 129.0, 128.6, 127.2, 126.1, 123.8, 104.9, 13 5, 142.0, 139.1, 133.7, 129.5, 129.5, 129.0, 127.0, 126.4, 123.9, 104.2, 26.7, 22.4; HR-MS (ESI) m/z [M + H] + calcd for C 18 H 20 N 3 278.1652278.…”

“…). 27 Reaction time 3 h; yield 93% (0.795 g); pale pink solid; R f = 0.28 in 20% EtOAc in n-hexane; mp 119−123 °C; IR (KBr, ν, cm −1 ) 3438, 1655,1619,1571,1519,1393,1059,1019,821,755; 1 H NMR (400 MHz, DMSO-d 6 ) δ 7.72 (d, J = 7.2 Hz, 1H), 7.51 (d, J = 8. 4 Hz,2H),7.42 (t,J = 6.8 Hz,1H),7.33 (dd,J = 7.6,1.6 Hz,1H),3H),4.89 (s,2H),2.34 (s,3H), 1.97 (s, 3H); 13 C{ 1 H} NMR (100 MHz, DMSO-d 6 ) δ 146.…”

“…0, 143.6, 136.8, 135.2, 134.0, 133.2, 132.7, 129.5, 128.9, 127.8, 125.3, 122.7, 104.0, 20.6, 12.9; HR-MS (ESI) m/z [M + H] + calcd for C 17 H 17 BrN 3 342.0600 and 344.0580,. 27 Reaction time 3 h; yield 98% (0.654 g); pale yellow solid; R f = 0.24 in 20% EtOAc in n-hexane; mp 165−168 °C; IR (KBr, ν, cm −1 ) 3437, 1615,1516,1429,1395,1324,1187,762,693; 1 H NMR (400 MHz, CDCl 3 ) δ 7.60−7.57 (m, 2H), 7.48 (t, J = 7. 6 Hz,2H),2H),7.15 (dt,J = 7.6,1 Hz,1H),1H),1H),3.94 (s,2H), 2.31 (s, 3H); 13 C{ 1 H} NMR (100 MHz, CDCl 3 ) δ 163.…”

“…0, 147.6, 142.3, 138.6, 134.6, 133.7, 129.5, 127.2, 123.8, 118.0, 115.8, 115.1, 105.3, 55.6, 12.9 5-Amino-4-(2-bromo-4,5-dimethoxyphenyl)-3-methyl-1-phenyl-1H-pyrazole (4s). 27 Reaction time 3 h; yield 98% (0.951 g); pale brown solid; R f = 0.16 in 20% EtOAc in n-hexane; mp 162−164 °C; IR (KBr, ν, cm −1 ) 3430, 2304,1618,1507,1463,1264,1208,1174,1064,896; 1 H NMR (700 MHz, CDCl 3 ) δ 7.62 (d, J = 7.7 Hz, 2H), 7.47 (t, J = 7.7 Hz, 2H), 7.33 (t, J = 7.7 Hz, 1H), 7.14 (s, 1H), 6.82 (s, 1H), 3.90 (s, 3H), 3.87 (s, 3H), 3.73 (s, 2H), 2.17 (s, 3H); 13 C{ 1 H} NMR (175 MHz, CDCl 3 ) δ 149. 1, 148.5, 147.9, 142.3, 138.9, 129.6, 127.1, 125.7, 123.8, 115.7, 115.6, 115.1, 105.3, 56.3, 56.2, 13. 5-Amino-4-mesityl-3-methyl-1-phenyl-1H-pyrazole (4t).…”

Organocatalytic Chemoselective C4‐Benzylation of 5‐Aminopyrazoles

“…The authors have cited additional references within the Supporting Information (Ref. [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]).…”