6 Indazoles and Related Heterocycles
Song and et al. discovered that N-aryl-N-(o-bromobenzyl)hydrazines 102 or
N-aryl-N
0 -(o-bromobenzyl)hydrazines 104 could be effected by the Pd(OAc) 2 /dppf
catalytic system to afford 2-aryl-2H-indazoles 103 [71] and 1-aryl-1H-indazoles
105 [72] with reasonable yields (Scheme 37). Further investigations indicated that
[N-aryl-N
0 -(o-bromobenzyl)hydrazinato-N
0 ]-triphenylphosphonium bromides 106 were
also suitable substrates for this reaction, affording 1-aryl-1H-indazoles 105 in
moderate yields.
The Katayama group applied the similar strategy for the construction of tetracyclic
heterocycles 108 (Scheme 38) [73]. Their amination substrates 107 were treated
with Pd(OAc) 2 /DPEphos to deliver coupling products 108. After deprotection and
Scheme 36 CuI/DMEDA-catalyzed synthesis of 1-aminoindolines and cinnolines
Scheme 37 Synthesis of 2-aryl-2H-indazoles and 1-aryl-1H-indazoles via Pd-catalyzed intramolecular C–N bond formation
Scheme 38 Pd-catalyzed synthesis of tetracyclic heterocycles
102
Y. Jiang and D. Ma