Pyrido indazole

Pyrido[ 1, 2 1,2]imidazo[4,5-b]quinoxaline nomenclature, 1, 22 2,2 -Pyridoin synthesis, 2, 337 Pyrido[ 1,2-6]indazoles synthesis, 5, 335 E ridoindoles rearrangement, 4, 508 Pyrido[a]indoles synthesis, 4, 233 Pyrido[6]indoles nomenclature, 4, 498 Pyridooxadiazolones ring contraction, 4, 149... 

Support for this suggestion comes from many quarters. Reduction of the jS-carboline anhydro-bases with sodium and alcohol or with tin and hydrochloric acid gives the 1,2,3,4-tetrahydro derivatives, as does catalytic reduction over platinum oxide in an alkaline medium. On the other hand, catalytic reduction with platinum oxide in acetic acid results in the formation of the 5,6,7,8-tetrahydro-j3-carbolinium derivatives (see Section III,A,2,a). It should be noted, however, that reduction of pyrido[l,2-6]indazole, in which the dipolar structure 211 is the main contributor to the resonance hybrid, could not be effected with hydrogen in the presence of Adams catalyst. 

Few heteroaryl-substituted 37/-azepines are known however, photolysis of 2-(2-azidophenyl)-pyridine (80) in diethylamine provides Ar,Ar-diethyl-3-(2-pyridyl)-3/f-azepin-2-amine(81), along with minor amounts of pyrido[3,2-6]indole (82) and the mesoionic pyridofl, 2-7>]indazole (83).191... 

The cyclization of 3-[2-[4-[(2-fluorophenyl)-(2-phenylhydrazono) methyl]-l-piperazinyl]ethyl]-2-methyl-4/7-pyrido[l,2-a]pyrimidin-4-one 452 in boiling ethylene glycol in the presence of potassium carbonate overnight gave indazole derivative 453 in 25% yield (90EUP353821, 90USP4957916). Ocaperidone 8 was obtained when the Z oxime 454 was stirred in toluene in the presence of aqueous potassium hydroxide at 45-55°C for 0.5 hour, then at reflux for 3 hours (91EUP453042). 

S-carboline (178) but cyclized to pyrido[l,2 ]indazole (176) Carboline 178 was however obtained by heating 3-azido-2-phenyl-pyridine (177) . 

Also in this field, Larock et al. have described that sydnones 29 undergo [3+2] dipolar cycloadditions with arynes affording 2//-indazoles 30 nndo" mUd reaction conditions. These heterocyclic derivatives are formed by a spontaneons extmsion of CO from the initial cycloadduct (Scheme 12.19) [30]. The same authors have developed a simple route to pyrido[l,2-f>]indazoles 31 via an aryne [3+2] cycloaddition with A(-tosylpyridininm imides and subsequent flnoride-induced elimination of the tosylate anion (Scheme 12.19) [31]. 

Annulation Reactions. Larock et al. have described the synthesis of different heterocyclic systems using a [3+2] annulation approach. For instance, pharmaceutically important pyrido[l,2-fl]indole derivatives such as 93 are easily accessible from 2-substituted pyridines and aryne precursors (Scheme 12.48) [83]. More recently, the 1/f-indazole skeleton has been accessed through a [3+2] annulation from arynes and hydrazones. The reaction with Al-arylhy-drazones leads to 1,3-disubstituted indazoles 94 through an annulation-oxidation process (Scheme 12.48). The use of iV-tosylhydrazones also affords 3-substituted-Ai(H)-indazoles, although probably via a [3+2] cycloaddition (see Scheme 12.18) with in situ generated diazo compounds [84]. 

Cl 7H1 iiNj r 5,11-Dimethyl-6H-pyrido[4,3-b]carbazole, 40B, 273 Cl7H1 N202 r 1-Phenyl-4,5-dihydro-7,8-dihydroxy-1H-benz[g]indazole, 43B, 363... 

SCHEME 10 Synthesis of pyrido[l,2-6]indazoles from arynes and pyridiruumN-miines [32]. 

Y. Yamashita, T. Hayashi, M. Masumura, Reactions of substituted pyridinium N-imines with benzyne synthesis of pyrido [1,2-6] indazoles... 

In 2013, the same group developed a novel Pd-catalyzed nitrogenation of arylpyridines 77 via C-H azidation. Direct C-N and N-N formations are achieved for this N-atom incorporation transformation using azides as the N-atom source (Scheme 7.54) [123]. This method provides an alternatively concise approach for the constmction of bioactively important pyrido[l,2-b]indazoles 78. 

Zheng Q-Z, Feng P, Liang Y-F, Jiao N (2013) Pd-catalyzed tandem C-H azidation and N-N bond formation of arylpyridines a direct approach to pyrido[l,2-b]indazoles. Oig Lett 15 (16) 4262- 265... 

---