Oxoammonium Salt Oxidations of Alcohols in the Presence of Pyridine Bases
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- 作者：James M. Bobbitt ; Ashley L. Bartelson ; William F. Bailey ; Trevor A. Hamlin ; Christopher B. Kelly
- 刊名：Journal of Organic Chemistry
- 出版年：2014
- 出版时间：February 7, 2014
- 年：2014
- 卷：79
- 期：3
- 页码：1055-1067
- 全文大小：604K
- ISSN：1520-6904
文摘
Oxoammonium salt oxidations (using 4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate) of alcohols containing a 尾-oxygen atom in the presence of pyridine yield dimeric esters, while in the presence of 2,6-lutidine the product is a simple aldehyde. The formation of a betaine between pyridine and an aldehyde is presented to explain this disparity in reactivity. The betaine is oxidized by the oxoammonium salt to give an N-acylpyridinium ion that serves as an acylating agent for ester formation. Steric effects deter the formation of such a betaine with 2,6-disubstituted pyridines. A series of alcohols containing a 尾-oxygen substituent were oxidized to aldehydes in the presence of 2,6-lutidine, and a short study of the relative reactivity of various alcohols is given. An overall mechanism for oxoammonium cation oxidations is suggested, premised on nucleophilic additions to the oxygen atom of the positively charged nitrogen鈥搊xygen double bond. Possible mechanisms for both dimeric oxidations and simple oxidations are given.