The development of highly selective methods for the synthesis of functionalized olefins, based on sequential catalytic reactions of organometallic reagents, has been the subject of extensive study because of their versatile applications in organic synthesis and materials science. The silylative coupling of olefins with vinyl-substituted organosilicon compounds (discovered in our group) represents one of the most efficient and straightforward methods for the synthesis of stereodefined alkenylsilanes and bis (silyl) alkenes, which are particularly attractive scaffolds for further transformations including palladium-catalyzed cross-coupling with organic halides (Hiyama coupling) or electrophile-induced desilylation. The article highlights the recent developments and covers the literature mainly from the last decade in the sequential (also one-pot) synthetic strategies including ruthenium-catalyzed silylative coupling followed by desilylative cross-coupling, acylation and halogenation, leading to stereodefined organic derivatives such as (E)-alkenyl halides, (E)-α,β-unsaturated ketones or arylene-(E)-vinylene derivatives which are widely applied as fine chemicals, functional materials or building blocks in organic synthesis. † Dedicated to Prof. Ei-ichi Negishi on the occasion of his 80th birthday.
E)-β-Iodoenamides and (E)-β-iodoenimides can be easily obtained from N-vinyl derivatives (N-vinylamides and N-vinylimides) by stereoselective ruthenium-catalysed silylative coupling with vinyltrimethylsilane (Marciniec coupling) and subsequent stereospecific silicon-iodine exchange. Bromodesilylation of (E)-β-silylenimides affords (E)-β-bromoenimides, while the analogous reactions involving (E)-β-silylenamides lead to decomposition of substrates. N-Halosuccinimides have been found as the most effective halogenating agents in the desilylation step under mild conditions. The ruthenium-catalysed silylation/halodesilylation sequence can be performed in a one-pot procedure.
A novel method for the synthesis of 1-silyl-substituted 1,3-butadienes, based on [RuHCl(CO)(PCy3)2]-catalyzed silylative coupling of terminal (E)-1,3-dienes with vinylsilanes, is reported. The reaction provides a facile and straightforward access to (E,E)-dienylsilanes in a highly stereoselective fashion (especially for aryl-substituted dienes) and opens a valuable and general synthetic route for the direct catalytic silylation of conjugated dienes with elimination of ethylene as a single byproduct. Preliminary results on synthetic application of the synthesized silylated 1,3-butadienes in desilylation reactions are described.
In nearly every total synthesis, silylating agents are employed in synthetic steps to protect sensitive functional groups. A Pt-catalyzed hydrosilylation of various unsaturated substrates to prepare novel symmetrical and unsymmetrical disilazanes is described. The developed synthetic methodology is widely applicable and tolerates all manner of functional groups (e.g., amines, ethers, esters, halogens, silanes, etc.). To demonstrate the value of the described method, mono-substituted 1,1,3,3-tetramethyldisilazanes were further selectively converted to completely new unsymmetrical derivatives.
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