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1.2.1 Arylsilicon Cross-Coupling Reactions

DOI: 10.1055/sos-SD-207-00195

Denmark, S.; Chang, W.-T. T.Science of Synthesis: Cross Coupling and Heck-Type Reactions, (20131383.

General Introduction

Silicon, the second-most abundant element in the Earthʼs crust, has played an enormous role in the development of new synthetic methods in organic chemistry since the 1960s. The special properties that silicon imbues on organic compounds provide unique opportunities to modulate chemical reactivity. Accordingly, silicon has been incorporated into a myriad of organic reagents to facilitate a variety of carbon—carbon and carbon—heteroatom bond-forming processes.[‌1‌‌5‌] The utility of silicon in the context of palladium-catalyzed cross-coupling reactions was first reported by Kumada in 1982.[‌6‌,‌7‌] However, research in this area did not advance significantly until six years after the initial reports, probably because of the narrow scope and inefficiency of the isolated hypervalent silane reagents employed. However, beginning in 1988, Hiyama and Hatanaka demonstrated a practical cross-coupling protocol that entails the in situ generation of a hypercoordinate silicate (siliconate) by the addition of a fluoride source to the more easily synthesized and stable tetracoordinate silanes.[‌8‌] This strategy is founded on the high enthalpy of formation of a Si—F bond (160 kcal · mol−1).[‌9‌,‌10‌] The hypercoordinate silicate is activated toward the critical transmetalation step; the mechanistic understanding of activated transmetalation is discussed in Section 1.2.1.1. On the basis of this framework, many research groups have developed catalytic systems suited for the coupling of various organosilanes. In fact, the remarkable diversity of organosilicon-based reagents is one of the most distinctive features of this chemistry and differentiates it from that of boron, tin, and other cross-coupling reagents. Silicon moieties bearing three carbon substituents, one to three chlorine or fluorine substituents, and one to three oxygen substituents are all known to participate in the cross-coupling reactions of aryl groups. Accordingly, the cross coupling of arylsilanes can be roughly organized into three major categories: triorganosilanes, halosilanes, and oxygen-substituted silanes. Because of the vast variety in the last category, it is further divided into smaller sections to facilitate presentation. Concluding remarks highlighting the strengths of some of the more useful types of arylsilane reagents are given at the end of the chapter in Section 1.2.1.4.

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References