Stereoselective aldol additions of achiral ethyl ketone-derived trichlorosilyl enolates

Origins of Diastereoselectivity in the Addition of Enoxysilanes to Vinyl Diazonium Salts

The addition of enoxysilanes to vinyl diazonium ions occurs with varying levels of diastereoselectivity. To understand the origins of the stereoselectivity, we studied these transformations using density functional theory (DFT) calculations. The selectivity stems from a stabilizing cation-π interaction that orients the nucleophile and the diazonium ion.

Catalytic enantioselective aldol reactions

Recent developments in catalytic asymmetric aldol reactions have been summarized.

Sequential Catalysis of Phosphine Oxide for Stereoselective Synthesis of Stereopentads

An efficient method for accessing enantiomerically pure stereopentads via a catalytic asymmetric sequential aldol reaction has been developed for the first time. The enantioselective sequential aldol reaction produces a wide range of chiral stereopentad precursors in good yields with excellent enantioselectivities. The key to success is the use of the sequential catalytic system involving a chiral phosphine oxide catalyst and trichlorosilyl triflate.

Aminophosphine Oxides: A Platform for Diversified Functions

This review summarizes significant contributions reported on aminophosphine oxides (AmPOs), specifically those containing at least one amino group present as amino substituents on α- and β-carbons including direct P-N bond containing molecules. AmPOs have additional 'N' site(s), including highly basic 'P=O' groups, and these features make favor smooth and unexpected behavior. The most striking manifestations of flexibility of AmPOs are that they are exciting ligand systems for the coordination chemistry of actinides, and their involvement in catalytic organic reactions including enantioselective opening of meso-epoxides, addition of silyl enol ethers, allylation with allyltributylstannane, etc. The diverse properties of the AmPOs and their metal complexes demonstrate both the scope and complexity of these systems, depending on the basicity of phosphoryl group, and nature of the substituents on the pentavalent tetracoordinate phosphorus atom and metal. Two components key to understanding the challenges of actinide separations are detailed here, namely, previously described separation methods, and recent investigations into the fundamental coordination chemistry of actinides. Both are aimed at probing the critical features necessary for improved selectivity of separations. This review leads to the conclusion that, although many AmPOs have already been discovered and developed over the past century, many opportunities nevertheless exist for further developments towards new extraction processes and new catalytic materials by fine tuning the electronic and steric properties of substituents on the central phosphorus atom.

Intramolecular [1,4]-S- to O-silyl migration: a useful strategy for synthesizing Z-silyl enol ethers with diverse thioether linkages

An intramolecular [1,4]-S- to O-silyl migration has been used to form silyl enol ethers with Z-configurational control. The silyl migration also creates a new anion center at sulfur, which can subsequently react with electrophiles to generate Z-silyl enol ethers with diverse thioether linkages. The synthetic utility of this pathway was demonstrated by modifying the Z-silyl enol ethers with aldehydes via a Mukaiyama aldol reaction or Prins cyclization to generate functionalized organosulfur compounds.

Lewis acid organocatalysts

Abstract The term Lewis acid catalysts generally refers to metal salts like aluminium chloride, titanium chloride and zinc chloride. Their application in asymmetric catalysis can be achieved by the addition of enantiopure ligands to these salts. However, not only metal centers can function as Lewis acids. Compounds containing carbenium, silyl or phosphonium cations display Lewis acid catalytic activity. In addition, hypervalent compounds based on phosphorus and silicon, inherit Lewis acidity. Furthermore, ionic liquids, organic salts with a melting point below 100 degrees C, have revealed the ability to catalyze a range of reactions either in substoichiometric amount or, if used as the reaction medium, in stoichiometric or even larger quantities. The ionic liquids can often be efficiently recovered. The catalytic activity of the ionic liquid is explained by the Lewis acidic nature of their cations. This review covers the survey of known classes of metal-free Lewis acids and their application in catalysis.

Catalytic Addition of Simple Alkenes to Carbonyl Compounds Using Group 10 Metals

Recent advances using nickel complexes in the activation of unactivated monosubstituted olefins for catalytic intermolecular carbon-carbon bond-forming reactions with carbonyl compounds, such as simple aldehydes, isocyanates, and conjugated aldehydes and ketones, are discussed. In these reactions, the olefins function as vinyl- and allylmetal equivalents, providing a new strategy for organic synthesis. Current limitations and the outlook for this new strategy are also discussed.