Selective Synthesis of 3-Arylbenzo-1,2,3-triazin-4(3H)-ones and 1-Aryl-(1H)-benzo-1,2,3-triazoles from 1,3-Diaryltriazenes through Pd(0) Catalyzed Annulation Reactions.

Abstract

Pd(0) catalyzed carbonylative annulation reaction of 1-(2-iodophenyl)-3-aryltriaz-1-enes in the presence of DABCO and 1 atm of carbon monoxide in toluene at 80 °C gave the corresponding 3-arylbenzo-1,2,3-triazin-4(3H)-ones with high selectivity and in excellent yields. Substrate scope of this reaction is demonstrated with 24 examples with various halo, alkyl, and alkoxy substituents on either of the aromatic rings. Bromo substituted triazenes were less reactive as starting materials toward the carbonylative annulation reaction and yielded 3-arylbenzo-1,2,3-triazin-4(3H)-ones in good to moderate yields in the presence of only xantphos as an additive. In the absence of CO (under N2 atmosphere), the reaction did not proceed, and only starting material was recovered. However, in the presence of catalytic amount of CO or in the presence of Ph3P in catalytic amounts as additives, the reactions proceeded to yield the corresponding 1-aryl-(1H)-benzo-1,2,3-triazoles selectively in good yields. On the basis of control experiments, a plausible reaction mechanism for the selective formation of 3-arylbenzo-1,2,3-triazin-4(3H)-ones in the presence of CO and1-aryl-(1H)-benzo-1,2,3-triazoles in the absence of CO through a common intermediate was proposed.