Development of New Organosiiicon Reagents and Its Application to Environmentally Benign Organic Synthesis

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1. Development of Synthetic Reagents Bearing a Dimethylsilyl Group and Its ApplicationThe aldol reaction of dimethylsilyl (DMS) enolates with aldehydes proceeded efficiently in the presence of alkali or alkali earth metal salts. As the result of reactions using various metal salts, it was found that metal chlorides show high activity and the reaction mechanism involves nucleophilic activation of silyl enolates. Interestingly, the aldol reaction proceeded even in the presence of water, and an aqueous solution of formaldehyde was usable. In the presence of magnesium chloride, DMS enolates reacted with α-mopes to give Michael adducts in good to high yields. Under similar conditions, DMS enolates also added to N-tosylimines. The Mannich-type reaction was effectively induced by the combined use of water and a catalytic amount of diisopropylamine. The base-catalyzed Mannich-type reaction showed high levels of diastereoselectivity. The aldol reactions of α-DMS-esters with aldehydes and ketones were effectively accelerated by alkali or alkali earth metal salts. The reaction with α-enones afforded aldol adducts in preference to Michael adducts. DMS ethers and DMS amines were found to be effective in the Lewis acid-catalyzed reductive etherification and amination of carbonyl compounds2. Radical Reactions Using Indium Catalysts and HydrosilanesIn the presence of a catalytic amount of indium(III) acetate, alkyl halides underwent reduction with phenylsilane to give alkanes in good yield. This reduction is tolerant to polar functionalities such as ether and ester groups. The reaction mechanism probably involves radical reduction with indium hydride species generated from indium(III) acetate and phenylsilane. The reduction system was applicable to an efficient intermolecular radical addition of alkyl halides to electron-deficient alkenes