Reduction of Electrophilic Substrates Lewis Acids

This Lewis acid-catalyzed electrophilic aromatic substitution allows the synthesis of alkylated products via the reaction of arenes with alkyl halides or alkenes. Since alkyl substituents activate the arene substrate, polyalkylation may occur. A valuable, two-step alternative is Friedel-Crafts Acylation followed by a carbonyl reduction. 

On the other hand, trialkylhydrosilanes are capable of reducing carbonyl compounds and some activated olefins in the presence of Brc nsted or Lewis acids. Apparently, coordination of carbonyl oxygen to acid is important to activate electrophilic carbons. We thought that pentacoordinate hydridosilicates should be a good hydride transfer reagent because of the intrinsic nucleophilicity, while the significant Lewis acid character of the silicon center should activate the substrate carbonyl compounds. Reduction of carbonyl compounds with pentacoordinate hydridosilicates are expected to proceed without any additives and thus very interesting from both mechanistic and practical point of view. 

The tailored dinuclear aluminium Lewis acid displayed a high Lewis-acid catalytic activity due to a double electrophilic activation of a substrate s carbonyl group. This skilful ligand design turned a standard alkoxide into a real multitool for carbonyl chemistry. This type of catalyst was employed for instance in Mukaiyama aldol reactions, in MPV reductions and Oppenauer oxidations and related Tischchenko coupling reactions. 

One of the most common uses of [ C]acetyl chloride is its Lewis acid- (AICI3, SnCLi) catalyzed Friedel-Crafts reaction with aromatic or heteroaromatic substrates to produce labeled aryl/heteroaryl methyl ketones. As these intermediates are subject to several types of transformations, they have been used as key intermediates for the synthesis of a wide variety of a,)8-functionalized aryl/heteroaryl alkyl target compounds. For example, aryl/ heteroaryl methyl ketones can be (a) halogenated in the methyl group to provide substrates for reaction with carbon or nitrogen nucleophiles, (b) deprotonated so as to react with appropriate electrophilic partners, (c) subjected to stereoselective carbonyl group reduction to alcohols, or (d) reduced to aryl/heteroaryl alkyls. Such transformations can be conducted sequentially in many combinations. 

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