Disilylated Compounds as Precursors of Heterocycles : Synthesis of Benzimidazoles, Triazoles, Furan and Pyrrole

Abstract

The cyclization of disilylated compounds catalyzed by trifluorornethanesulfonic acid is an easy way to obtain some heterocycles such as benzimidazole, triazole, furan and pyrrole.In-recent years, organosilicon reagents have found many applications in organic synthesis' : in the field of heterocyclic chemistry, the cyclization of silylated n compounds has been reported to give cyclic ethers' and carbamates , lactones , lactames , oxazolones6 and mesoionic oxazolones , imidazolidinediones , triazolones , oxadiazoles'O and aminotriazinones . 3 4 4 7 8 9 11 A general scheme appears from these cyclizations as well as from the heterocyclizations resulting of the 167 Copyright 0 1988 by Marcel Dekker, lnc.

The Chemistry of Hydrazonates

“…Similar reaction of 1-acetylsemicarbazide (82) with chlorotrimethylsilane (78) yielded also the hydrazonate ester 83 [69]. CH Reaction of trihalosilane with N,N-dimethyl acidhydrazides 84 was reported to give the cyclic hydrazonates 85 [70].…”

“…Trimethylsilyl ethanehydrazonate ester 163 reacted with trifluoromethanesulfonic acid and yielded the 1,2,4-triazol-5one derivative 165 [69].…”

Five‐Membered Heterocycles: 1,3‐Azoles

“…A modification has been introduced to prepare 1-acetyl-2-methylbenzimidazole (257) in quantitative yield (Scheme 10.145) [419].…”

Product Class 4: Benzimidazoles

“…5-Fluoro-1-(trifluoroacetyl)-1H-benzimidazole-2(3H)-thione; Typical Procedure: [67] A mixture of N-(2-amino-4-fluorophenyl)-2,2,2-trifluoroacetamide (6.7 g, 30 mmol), KOH ( [70,74±79] and boric acid, [80] hexamethyldisilazane in the presence of a catalytic amount of triflic acid, [81] heating with titanium catalyst, [82] heating under pressure, [83] and use of photolytic conditions. [84] The major problem with the Phillips reaction is that the amino groups compete with the carboxylic acid carbonyl group for the acid-catalyst proton, and this naturally inhibits the nucleophilic addition to that carbonyl group.…”

“…1-Acetyl-2-methyl-1H-benzimidazole (47): [81] A (49). [199] The analogous diisothiocyanate 48 (Y = S) is converted into the 1H-benzimidazole-2(3H)-thione 50 in about 60% yield when heated with methanol (Scheme 28).…”