Chloroformamidinium salts: Efficient reagents for preparation of 2‐aminobenzoimidazole, 2‐aminobenzoxazole, and 2‐aminobenzothiazole derivatives

Abstract magnified image A Reaction involving chloroformamidinium salts (TCFH 1a, BTCFH 1b, DmCFH 1c, DmPCFH 1d, BPCFH 1e) and 2‐aminophenol 9a, benzene‐1,2‐diamine 9b, and 2‐aminothiophenol 9c afforded 2‐aminobenzoxazole 13, 2‐aminobenzoimidazole 14, and 2‐aminobenzothiazole 15 derivatives, respectively as major products, due to the in situ heterocyclization with dimethylamine acting as the better leaving group. Attempts for preparation of 13‐15 from the reaction of N,N‐dimethyl carbomyl chloride 16 with 2‐aminophenol 9a, benzene‐1,2‐diamine 9b, and 2‐aminothiophenol 9c were unsuccessful, and gave the unexpected products benzoxazol‐2‐ol 18a, benzoimidazol‐2‐one 18b, and S‐(2‐amino‐phenyl) N,N‐dimethylthiocarbamate 19 respectively. On the other hand reaction of chloroformamidinium salts 1a‐e with 3‐benzyl‐2‐hydrazinoquinoxaline 3 and 1‐hydrazinophthalazine hydrochloride 4 in the presence of triethylamine as a base, afforded the [1,2,4]triazolo derivatives 6 and 7 respectively in good yield and purity. These triazole derivatives were formed due to the strong tendency towards heterocyclization and substitution of dimethylamine group as a better leaving group.