New efficient synthesis of 4-aminocarbonyl substituted 4H-3,1-benzoxazines by a Passerini 3CC/Staudinger/aza-Wittig sequence |
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Authors: | Ping He |
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Institution: | Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, Central China Normal University, Wuhan, 430079, PR China |
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Abstract: | α-Acyloxy-carboxamide azides 1, obtained from Passerini reaction of easily accessible o-azidobenzaldehyde with isocyanides and carboxylic acids, reacted with triphenylphosphine to give various 4-aminocarbonyl substituted 4H-1,3-benzoxazines 3 in moderate to high yields via sequential Staudinger and intramolecular aza-Wittig reaction. However, α-hydroxy carboxamide azides 5 were obtained in moderate yields when pyruvic acid was used in the Passerini reaction. Further sequential reaction of azides 5 with triphenylphosphine and isocyanates produced 2-amino-4-aminocarbonyl substituted 4H-1,3-benzoxazines 8 via a tandem Staudinger/aza-Wittig/heterocumulene-mediated annulation. |
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