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Isolation and Racemization Mechanism of Optically Active Benzylmethylphenyltelluronium Salts
Author(s) -
Shimizu Toshio,
Sakurai Ryuuya,
Azami Yoko,
Hirabayashi Kazunori,
Kamigata Nobumasa
Publication year - 2010
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201000893
Subject(s) - chemistry , racemization , diastereomer , iodide , nucleophile , bromide , tetrafluoroborate , medicinal chemistry , sulfonium , hexafluorophosphate , organic chemistry , ionic liquid , catalysis , salt (chemistry)
Diastereomeric benzylmethylphenyltelluronium (1 S )‐(+)‐ and (1 R )‐(–)‐camphor‐10‐sulfonates were synthesized and resolved by fractional recrystallization. The absolute configurations of the isomers were determined by X‐ray crystallographic analysis. Enantiomerically pure telluronium salts with achiral counteranions, such as tetrafluoroborate, 4‐chlorobenzenesulfonate, bromide, iodide, and tetraphenylborate, were also obtained by anion‐exchange reactions of the separated diastereomers. The optically active telluronium salts possessing counteranions with a high nucleophilicity, such as bromide and iodide, were found to racemize in solution. The racemization of the telluronium salts was found to proceed either through the formation of a tellurane by the nucleophilic addition of a counteranion to the tellurium atom followed by decomposition into methyl phenyl telluride and benzyl halide or by several pseudorotations of the tellurane.