Organosilicon Chemistry

Novel Approaches and Reactions

Tamejiro Hiyama, Martin Oestreich, Tamejiro Hiyama, Martin Oestreich

• Publisher: Wiley-VCH
• Year: 2019
• ISBN:
  9783527814770
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

Provides a unique summary of important catalytic reactions in the presence of silicon A must-have for all synthetic chemists, this book summarizes all of the important developments in the application of organosilicon compounds in organic synthesis and catalysis. Edited by two world leaders in the field, it describes different approaches and covers a broad range of reactions, e.g. catalytic generation of silicon nucleophiles, Si-H Bond activation, C-H bond silylation, silicon-based cross-coupling reactions, and hydrosilylation in the presence of earth-abundant metals. In addition to the topics covered above, Organosilicon Chemistry: Novel Approaches and Reactions features chapters that look at Lewis base activation of silicon Lewis acids, silylenes as ligands in catalysis, and chiral silicon molecules. -The first book about this topic in decades, covering a broad range of reactions
-Covers new approaches and novel catalyst systems that have been developed in recent years
-Written by well-known, international experts in the areas of organometallic silicon chemistry and organosilicon cross-coupling reactions Organosilicon Chemistry: Novel Approaches and Reactions is an indispensable source of information for synthetic chemists in academia and industry, working in the field of organic synthesis, catalysis, and main-group chemistry.

1
Catalytic Generation of Silicon Nucleophiles

Koji Kubota and Hajime Ito

Institute for Chemical Reaction Design and Discovery (WPI‐ICReDD), Hokkaido University, Sapporo, Hokkaido, 060‐8628, Japan

Faculty of Engineering, Division of Applied Chemistry and Frontier Chemistry Center, Hokkaido University, Kita 13 Nishi 8, Kita‐ku, Sapporo, Hokkaido, 060‐8628, Japan

1.1 Introduction

Silicon nucleophiles represent a class of important organometallic species for silicon–carbon, silicon–silicon, and silicon–boron bond formation reactions in synthetic chemistry [1]. Conventionally, the generation of silicon nucleophiles is accomplished by reactions of chlorosilanes with alkali metal (K, Na, Li), reactions of hydrosilanes with alkali metal hydride, cleavage of the silicon–silicon bond in disilanes or the silicon–boron bond in silylboron reagents by organometallic carbon nucleophiles, and transmetallation from other silicon‐metal compounds [2]. However, these stoichiometric methods have significant limitations such as low functional‐group compatibility due to the high reactivity of hard silyl anions with an alkali metal countercation. In this context, silicon‐based organocuprates are widely used as soft silyl anion equivalents for silicon–carbon bond formation reactions, even though this method requires stoichiometric organometallic compounds and copper salt [3]. Recently, catalytic nucleophilic silylation reactions have attracted considerable attention because of their mild reaction conditions and unique selectivity and reactivity. This chapter mainly focuses on two types of activation modes for catalytic generation of silicon nucleophiles (Figure 1.1). First, transmetalation between silicon compounds containing a Si─X bond (X = Si, B, and Zn) and metal catalysts generates nucleophilic silyl metal intermediates (Figure 1.1a). Second, a catalytic amount of Lewis bases (Nu) activates the silicon–boron bond of silylboron reagents to form nucleophilic silyl species (Figure 1.1b). This chapter provides the recent advancements in the catalytic generation of silicon nucleophiles through these activation pathways and their applications in organic synthesis.

Figure 1.1 Representative pathways for catalytic generation of silicon nucleophiles. (a) Metal‐catalyzed method. (b) Lewis base‐catalyzed method.

1.2 Silicon Nucleophiles with Copper Catalysts

1.2.1 Copper‐Catalyzed Nucleophilic Silylation with Disilanes

1.2.1.1 Silylation of α,β‐Unsaturated Carbonyl Compounds

In 1998, the first example of copper‐catalyzed nucleophilic 1,4‐silylation of α,β‐unsaturated carbonyl compounds with disilanes was reported by Ito et al. (Scheme 1.1) [4]. The reaction of cyclohexanone with a disilane in the presence of a copper salt and Bu₃P as a ligand proceeded to give the corresponding 1,4‐silyl addition product in high yield. The silylation presumably goes through the σ‐bond metathesis between a copper salt and a disilane to form the silylcopper intermediate, followed by its 1,4‐addition to cyclohexanone. The copper catalyst is regenerated by the reaction between the resultant copper enolate and silyl triflate, which is formed at the first stage of this cycle. This mild protocol can be applied to a variety of substrates such as α,β‐unsaturated cyclic and linear ketones and aldehydes to form the β‐silyl carbonyl compounds in high yields.

Scheme 1.1 Copper‐catalyzed silylation of α,β‐unsaturated carbonyl compounds with a disilane.

1.2.1.2 Silylation of Alkylidene Malonates

Scheidt and coworkers reported the copper‐catalyzed nucleophilic silylation of alkylidene malonates with disilanes in 2004 (Scheme 1.2) [5]. They found pyridine to be an effective ligand rather than phosphines for this reaction.

Scheme 1.2 Copper‐catalyzed silylation of alkylidene malonates with a disilane.

1.2.1.3 Silylation of Allylic Carbamates...