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Selective Organic Reactions Based on Novel Reactive Species Generated by Organometallic Reagents

基于有机金属试剂产生的新型反应物质的选择性有机反应

基本信息

批准号：
13640589
负责人：
HOJO Makoto
金额：
$ 2.24万
依托单位：
University of Tsukuba
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2002
项目状态：
已结题

项目摘要

Chromium(II) reagents are well recognized to be a one-electron reductant and have been used for selective organic synthesis. We found that an equimolar amount of an alkylchromium ate-type reagent, prepared from chrornium(III) chloride and alkyllithium reagent, reacted as a reductant with allyl and propargyl phosphates to produce the corresponding allyl- and propargylchromium reagents, respectively, and the generated allylic and propargylic reagents reacted as a nucleophile with a variety of electrophiles.We also found that enolates were reductively generated by the reaction of carbonyl compounds bearing a leaving group at the α-position with an equimolar amount of a chromium ate-type reagent, where the chromium reagent serves as a formal two-electron reductant. Previously, it was reported that α-bromo ketones, esters, and amides reacted with aldehydes and ketones in the presence of a chrpmium(II) reagent as a reductant to produce cross-aldol products under the Barbier-type conditions, while a stepwise reaction by the so-called Grignard-type procedure was not successful ; namely, after the generation of enolates from bromo ketone with chromium(II) in the absence of an electrophile, the enolate was not trapped with the electrophile. We succeeded in the reductive generation of enolates by a chromium ate-reagent and elucidated the characteristic feature of the Grignard-type reactions of the generated enolates with a variety of electrophiles.These enolates did not react with oxiranes, while in the presence of a Lewis acid, homoaldol product and aldol product were obtained, depending on the Lewis acid used. The aldol adduct was possibly produced by the reaction of chromium enolate with aldehyde that was formed through cationic rearrangement of oxirane in the presence of the Lewis acid.

铬（II）试剂被公认为是一种单电子还原剂，并已用于选择性有机合成。我们发现等摩尔量的由氯化铬（III）和烷基锂试剂制备的烷基铬酸盐型试剂作为还原剂与烯丙基和炔丙基磷酸盐反应，分别生成相应的烯丙基和炔丙基铬试剂，烯丙基和炔丙基试剂作为亲核试剂与多种亲电试剂发生反应，烯醇化物的生成是通过烯丙基和炔丙基试剂与亲电试剂的还原反应进行的。在α-位带有离去基团的羰基化合物与等摩尔量的铬酸盐型试剂反应，其中铬试剂用作形式双电子还原剂。以前曾报道α-溴代酮、酯和酰胺与醛和酮在铬（II）试剂作为还原剂存在下在Barbier型条件下反应生成交叉羟醛产物，而通过所谓的Grignard型程序的逐步反应不成功;即在不存在亲电试剂的情况下由溴酮与铬（II）生成烯醇化物后，烯醇化物不被亲电试剂捕获。用铬酸盐试剂成功地还原生成了烯醇化物，并阐明了所生成的烯醇化物与各种亲电试剂的Grignard型反应的特征，这些烯醇化物不与环氧乙烷反应，而在刘易斯酸存在下，根据所用的刘易斯酸的不同，得到了高醛醇产物和醛醇产物。在刘易斯酸存在下，环氧乙烷发生阳离子重排反应生成醛，然后烯醇化铬与醛反应生成羟醛加成物。