Iridium-Catalyzed Arene Ortho-Silylation by Formal Hydroxyl-Directed C−H Activation
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Abstract:
A strategy for the ortho-silylation of aryl ketone, benzaldehyde, and benzyl alcohol derivatives has been developed in which a hydroxyl group formally serves as the directing element for Ir-catalyzed arene C−H bond activation. One-pot generation of a (hydrido)silyl ether from the carbonyl compound or alcohol is followed by dehydrogenative cyclization at 80−100 °C in the presence of norbornene as a hydrogen acceptor and the combination of 1 mol % [Ir(cod)OMe]2 and 1,10-phenanthroline as a catalyst to form benzoxasiloles. The synthetic utility of the benzoxasilole products is demonstrated by conversion to phenol or biaryl derivatives by Tamao−Fleming oxidation or Hiyama cross-coupling. Both of these transformations of the C−H silylation products exploit the Si−O bond in the system and proceed by activation of the silyl moiety with hydroxide, rather than fluoride.Keywords:
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Silyl ether
Benzaldehyde
Abstract Thermolysis of HMePhSiSiMe3 in the presence of a catalytic amount of Ir{η2-Me2Si(CH2)2PPh2} (PMe3)3 resulted in the redistribution of substituents to give its isomer HMe2SiSiMe2Ph. We propose the mechanism involving the 1,3-Me-shift on a silyl(silylene) complex, which was trapped as a donor-stabilized silyl(silylene)iridium(III) complex.
Silylene
Redistribution
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Selective dehydrogenative silylation is one of the most valuable tools for synthesizing organosilicon compounds. In this study, a regio- and stereoselective ruthenium-catalyzed dehydrogenative intermolecular silylation was firstly developed to access (E)-alkenyl silyl-ether derivatives and silyl-ether heterocycles with good functional group tolerance. Furthermore, two pathways for RuH2(CO)(PPh3)3/NBE-catalyzed dehydrogenative intermolecular silylation of alcohols and alkenes as well as intermolecular silylation of naphthol derivatives were investigated with H2SiEt2 as the hydrosilane reagent.
Silyl ether
Organosilicon
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Silyl ether
Silyl enol ether
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In the presence of the clay montmorillonite, silyl ketene acetals and a silyl ether react with α,β-unsaturated esters and ketones to afford the corresponding Michael adducts in the form of the silyl ketene acetals and silyl enol ethers in good yields.
Silyl ether
Silyl enol ether
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Silyl ether
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Hydroxyl moieties are highly prevalent in natural products. We previously reported a chemoselective strategy for enrichment of hydroxyl-functionalized molecules by formation of a silyl ether bond to a resin. To generate smaller pools of molecules for analysis, we developed cleavage conditions to promote stepwise release of phenolic silyl ethers followed by aliphatic silyl ethers with a "tamed" version of the superbase 1,1,3,3–tetramethylguanadine. We demonstrate this as a general strategy for selective deprotection of phenolic silyl ethers under neutral conditions at room temperature.
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Abstract Preparative methods of polymers containing a silicon-oxygen bond in the main-chain are systematically summarized with emphasis on recent developments in the synthesis of polycarbosiloxanes, poly(silyl ether)s, and poly(silyl ester)s. Keywords: Silicon-oxygen-containing polymerspolysiloxanespolycarbosiloxanespoly(silylether)spoly(silyl ester)s
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Abstract A few of acyclic and cyclic silyl ethers were firstly synthesized in good yields by reactions of silyl triflimides with alcohol or ether. The corresponding silyl triflimides were easily produced by protodesilylation of phenyl or allyl silanes with HNTf 2 . All new compounds were characterized by 1 H NMR, 13 C NMR, MS, IR and HRMS.
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