Strategies To Prepare and Use Functionalized Organometallic Reagents

详细信息    查看全文

• 作者：Thomas Klatt ; John T. Markiewicz ; Christoph S盲mann ; Paul Knochel
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：May 16, 2014
• 年：2014
• 卷：79
• 期：10
• 页码：4253-4269
• 全文大小：1039K
• 年卷期：v.79,no.10(May 16, 2014)
• ISSN：1520-6904

文摘

Polyfunctional zinc and magnesium organometallic reagents occupy a central position in organic synthesis. Most organic functional groups are tolerated by zinc organometallic reagents, and Csp²-centered magnesium organometallic reagents are compatible with important functional groups, such as the ester, aryl ketone, nitro, cyano, and amide functions. This excellent chemoselectivity gives zinc鈥?and magnesium鈥搊rganometallic reagents a central position in modern organic synthesis. Efficient and general preparations of these organometallic reagents, as well as their most practical and useful reactions, are presented in this Perspective. As starting materials, a broad range of organic halides (iodides, bromides, and also to some extent chlorides) can be used for the direct insertion of magnesium or zinc powder; the presence of LiCl very efficiently promotes such insertions. Alternatively, aromatic or heterocyclic bromides also undergo a smooth bromine鈥搈agnesium exchange when treated with i-PrMgCl路LiCl. Alternative precursors of zinc and magnesium reagents are polyfunctionalized aryl and heteroaryl molecules, which undergo directed metalations with sterically hindered TMP bases (TMP = 2,2,6,6-tetramethylpiperide) of magnesium and zinc. This powerful C鈥揌 functionalization method gives access to polyfunctional heterocyclic zinc and magnesium reagents, which undergo efficient reactions with numerous electrophiles. The compatibility of the strong TMP-bases with BF₃路OEt₂ (formation of frustrated Lewis pairs) dramatically increases the scope of these metalations, giving for example, a practical access to magnesiated pyridines and pyrazines, which can be used as convenient building blocks for the preparation of biologically active molecules.