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TMSCl Promoted Acylation of Amines with 5-(α-amino- α\'-hydroxy)methylene Meldrum\'s Acids – Elucidation of Mechanism.
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1  Department of Organic Chemistry, Faculty of Chemistry, Gdansk University of Technology, Narutowicza 11/12; Gdańsk 80-233, Poland

Abstract: Recently we have observed accelerating influence of trimethyl silyl chloride addition on the rate of the reactions of 5-(α-amino- α\'-hydroxy)methylene Meldrum\'s Acids with amines particularly in the case of highly basic amines. However the nature of the aforementioned process remain unexplained. In proposed communication we wish to report insightful elucidation of this mechanism. The reaction under investigation involves simply addition of the trimethyl silyl chloride to the mixture of amine and carbamoyl Meldrum\'s acid derivative. We considered three potentially possible ways for the TMSCl action. The first possibility is formation of the O-silylated Meldrum acid, which would exclude formation of salt Meldrum\'s acid with amine, what undoubtedly hindered this reaction. The next way for the acceleration of the process is silylation of amine and subsequent reaction of silylated amine with carbamoyl Meldrum\'s acid. The last possibility is connected with the formation of equimolar amount of HCl during the reaction of TMSCl with carbamoyl Meldrum\'s acid or amine which should speed up the rate of decomposition of the Meldrum\'s acid derivative. The NMR monitored experiments as well classical experiments in which predicted intermediated were added to the reaction mixtures excluded formation of O-silylated Meldrum\'s acid as well as influence of formed HCl as a reason of the acceleration investigated reaction. Our experiments revealed that silylated amine is responsible for rate acceleration of the reaction amines and 5-(α-amino- α\'-hydroxy)methylene Meldrum\'s Acids in the presence of TMSCl.
Keywords: acylation, ketene, Meldrum\'s acid,