Aplicação do ácido α-fenilglioxílico como agente acilante na síntese de 2- arilbenzotiazóis e 1,4-benzoxazin-2-onas, utilizando Oxalato de Nióbio Amoniacal (ANO) como catalisador

Abstract

In this work was developed a new methodology for the synthesis of 2-substituted benzothiazoles 3 and 3-substituted benzoxazin-2-ones 5 using α-phenylglyoxylic acid (PGA) and its derivatives 1 as an acyl transfer agent. The reactions were catalyzed by ammonium niobium oxalate (ANO) using PEG-400 as solvent under conventional heating or ultrasound irradiation (US). In order to obtain the 2-substituted benzothiazole 3 were used 2-aminobenzothiazole 2 as starting materials, while o-aminophenol 4 were the precursors of the 1,4-benzoxazin-3-ones 5. The methodology allowed the preparation of seven 2-substituted benzothiazole 3 and nine 3-substituted 1,4-benzoxazin-2-ones 5 in yields between 35-85% for the compounds 3 and between 65-93% for the compounds 5. The o-aminobenzenethiol 2 and its derivatives react slower (up to 6h) than the similar phenols 4 (up to 2.5 h); however, the reaction times were reduced to 1 h (in the case of the o-aminobenzenethiol 2) and 15 min (for the 2-aminophenols 4) where the oil bath (100 ºC) was substituted by an ultrasound probe. There are many features in this methodology which make this one environmental friendly, such as, the using of ANO as a cheap and available catalyst, PEG-400 as a green solvent and US as a non-classical energy source. Besides, the unique reaction byproduct is CO2, which increase its atomic efficiency compared to other methodologies described before.