Approach Toward Reversal of Chemoselectivity in Catalytic Silylation of Pyranosides
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Abstract It is widely recognized that primary hydroxy groups show much higher reactivity than the secondary ones, especially in trialkylsilylation. Actually, DMAP‐catalyzed silylation of unprotected pyranosides gave the 6‐ O ‐silylate exclusively by silylation of the primary C(6)−OH. On the other hand, catalyst ent ‐ C1 overcame the general tendency of silylation, and enabled the selective silylation of the secondary C(3)−OH of two β‐glucopyranosides and a β‐galactopyranoside. Although the yields of the silylation are poor at this stage, this is the first example of selective silylation of the secondary hydroxy group in the presence of the free primary C(6)−OH of pyranosides under the catalyst‐controlled conditions.Keywords:
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Comprehensive Summary This paper presents the first general examples of palladium‐catalyzed desulfinative cross‐coupling reaction of polyhalogenated aryl triflates with aryl sulfinate salts showing an inversion of the conventional reactivity order of C—Br > C—Cl > C—OTf. The catalyst system, comprising of Pd(OAc) 2 and t BuPhSelectPhos , exhibited excellent catalytic reactivity and chemoselectivity toward this reaction. This reaction had a wide range of substrate scopes and provided a simple and efficient method for the construction of functionalized biaryl motifs. Notably, the C—H···Pd interaction from the methine hydrogen of the C2‐cyclohexyl group of the indolyl phosphine ligand with the Pd center may contribute a key factor in reactivity and chemoselectivity. Assisting with density functional theory (DFT) calculations, the results revealed that the oxidative addition step in this reaction was a controlling‐chemoselectivity step.
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The chemoselectivity of perakine reductase (PR) was engineered through rational design. We identified Arg127 as a control site of chemoselectivity. Mutation of Arg127 switched the chemoselectivity of PR between CO and CC or led to non-selectivity towards α,β-unsaturated ketones, leading to the production of allylic alcohols, saturated ketones, or a mixture of both. This study provides an example for developing novel reductases for α,β-unsaturated ketones.
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A metal carbenoid is a highly active carbon species that exhibits divergent reactivity. The control of the reactivity still remains a challenging task in carbenoid chemistry. Recently, several groups have succeeded in controlling the chemoselectivity of these reactions. This mini-review highlights substrate-controlled chemoselective arene cyclopropanation over C-H insertion reaction, and catalyst-controlled C-H functionalization of electron-rich aromatic compounds.
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Chemoselectivity Chemoselectivity is observed where one outcome is preferred in a reaction. There are actually two definitions that we need to consider. A chemoselective reaction is one in which one functional group reacts preferentially to another in a particular reaction. A chemoselective reaction...
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