Nucleophilic Activation of Hydrosilanes via a Strain-Imposing Strategy Leading to Functional Sila-aromatics

Carefully designed cyclic hydrosilanes enable trans-selective hydrosilylation of unactivated alkynes without transition metal catalysts via silicate formation. Employment of sterically demanding bidentate ligands of silicon increases steric congestion upon silicate formation, and this strain-imposing strategy facilitates hydride transfer. This hydrosilylation provides efficient access to diverse benzosiloles, silaphenalenes, and related silacycles.

In situ formed acetals facilitated direct Michael addition of unactivated ketones

A facile Michael addition of unactivated ketones under Brønsted acid conditions for the synthesis of 1,5-diketones.

TiO2 nano crystallites catalyzed water mediated microwave assisted regioselective three component domino hydrolysis/aldol condensation/Michael addition reaction of 3-(1,5-dioxo-1,5-diphenylpentan-3-yl)quinolin-2(1H)-one

Microwave supported, water intervened, nano crystalline TiO₂ catalyzed synthesis of 3-(1,5-dioxo-1,5-diphenylpentan-3-yl)quinolin-2(1H)-ones, is described.

Lewis base catalysis of the Mukaiyama directed aldol reaction: 40 years of inspiration and advances

Since the landmark publications of the first directed aldol addition reaction in 1973, the site, diastereo-, and enantioselective aldol reaction has been elevated to the rarefied status of being both a named and a strategy-level reaction (the Mukaiyama directed aldol reaction). The importance of this reaction in the stereoselective synthesis of untold numbers of organic compounds, both natural and unnatural, cannot be overstated. However, its impact on the field extends beyond the impressive applications in synthesis. The directed aldol reaction has served as a fertile proving ground for new concepts and new methods for stereocontrol and catalysis. This Minireview provides a case history of how the challenges of merging site selectivity, diastereoselectivity, enantioselectivity, and catalysis into a unified reaction manifold stimulated the development of Lewis base catalyzed aldol addition reactions. The evolution of this process is chronicled from the authors' laboratories as well as in those of Professor Teruaki Mukaiyama.

First sequential Mukaiyama-Michael reaction/crossed-Claisen condensation using two molar ketene silyl acetals and one molar alpha,beta-unsaturated esters promoted by a NaOH catalyst

The NaOH-catalyzed first sequential Mukaiyama-Michael reaction/crossed-Claisen condensation is developed using two molar ketene silyl acetals and one molar alpha,beta-unsaturated esters in either a stepwise or one-pot manner.

Lewis Base-Catalysed Mukaiyama–Aldol Reaction of Trimethylsilyl Enolates with Aldehydes

An efficient Mukaiyama-type aldol reaction of three typical silyl enolates, such as 1-(trimethylsiloxy)-1-methoxy-2-methyl-2-propene, 1-phenyl-1-trimethylsilyloxyethene and 1, 2-bis(trimethylsiloxy)cyclobutene, with aryl aldehydes and α,β–unsaturated aldehydes catalysed by 5 mol% of Lewis base catalyst 4-O2NPhOMgI in dichloromethane is described. The reaction proceeds under mild reaction conditions in good to excellent yields.

Lewis Base Catalyzed Mannich-Type Reactions between Trimethylsilyl Enol Ethers and Aldimines

Lewis base catalyzed Mannich-type reaction between trimethylsilyl enol ethers and N-tosylaldimines is described. Nitrogen anions generated from amides or imides such as lithium benzamide or potassium phthalimide are found to be effective Lewis base catalysts in DMF at room temperature to afford the corresponding beta-amino carbonyl compounds in good to high yields; the oxygen anion generated from carboxylic acids such as lithium acetate was also found to be effective in dry DMF. The above-mentioned lithium acetate-catalyzed Mannich-type reaction between aldimines and various trimethylsilyl (TMS) enol ethers such as silyl ketene acetal proceeded smoothly even in water-containing DMF. Then, Lewis base catalyzed three-component Mannich-type reactions of TMS enol ether, tosylamide, and aromatic aldehyde having electron-withdrawing group such as p-nitrobenzaldehyde were investigated. The reaction proceeded smoothly to afford the corresponding beta-amino ester in good yield. Further, ammonium carboxylates such as tetrabutyl ammonium acetate or tetrabutyl ammonium benzoate were found to be more effective Lewis base catalysts in the above-mentioned Mannich-type reaction. The synthesis proceeded in various solvents at lower temperatures. The reaction between aldimines and TMS enol ethers generated from thioester and various ketones such as propiophenone or cyclohexanone also proceeded smoothly to afford the corresponding beta-amino carbonyl compounds in high yields with good to high anti-selectivities.