Reagent-Controlled Divergent Synthesis of 2-Amino-1,3-Benzoxazines and 2-Amino-1,3-Benzothiazines
2019
Putta, V. P Rama Kishore | Vodnala, Nagaraju | Gujjarappa, Raghuram | Tyagi, Ujjawal | Garg, Aakriti | Gupta, Sreya | Pujar, Prasad Pralhad | Malakar, Chandi C.
A reagent-controlled chemoselective process has been devised for the synthesis of 4H-1,3-benzoxazines and related biologically important heterocycles in high yields under mild conditions. These scaffolds could be efficiently constructed using two different chemoselective reactions that rely on the choice of reagents and reaction conditions. The treatment of various 2-amino-arylalkyl alcohols with isothiocyanates afforded thiourea intermediates, which were reacted in situ with molecular iodine in the presence of triethylamine to give 2-amino-4H-1,3-benzoxazines, whereas the corresponding 2-amino-4H-1,3-benzothiazines were obtained by the reaction of thiourea intermediates in the presence of T3P (a mild cyclodehydrating agent) and triethylamine as the base. The described protocol represents the first example for the synthesis of 4H-1,3-benzoxazines via the dehydrosulfurization method using molecular iodine as the reagent.
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