On the mechanism of the organocatalytic asymmetric epoxidation of α,ß-unsaturated aldehydes.

Mechanistic studies on the organocatalytic epoxidation of α,ß-unsaturated aldehydes explore the autoinductive behavior of the reaction and establish that the hydrate/peroxyhydrate of the product is acting as a phase-transfer catalyst. Based on these studies, an improved methodology that provides high selectivities and decreased catalyst loading, through the addition of chloral hydrate, is developed.

Trienamines in asymmetric organocatalysis: Diels-Alder and tandem reactions.

The discovery of a novel activation mode provided by organocatalysis is presented. It is demonstrated that the merger of optically active secondary amines and polyenals generates reactive trienamine intermediates, which readily participate in Diels-Alder reactions with different classes of dienophiles, hence, providing a facile entry to highly complex molecular frameworks with excellent stereocontrol. For the Diels-Alder reactions with 3-olefinic oxindoles, spirocyclic oxidoles are formed in high yields, and with enantioselectivities in the range of 94-98% ee. It is demonstrated, that some of these products can be transformed into the hexahydrofuro[2,3-b]indole fragment. The organocatalytic trienamine concept has been extended to also include Diels-Alder reactions of olefins substituted with cyanoacetates providing multifunctional cyclohexenes with three contiguous stereocenters in high yield and good stereocontrol. The novelty of this activation strategy lies within the perfect chirality relay over a distance of up to eight bonds. Moreover, we also present the first trienamine tandem reaction by combining trienamine catalysis with enamine activation. In addition to the experimental results, a detailed mechanistic survey is also provided including NMR spectroscopic studies and calculations of the reactive trienamine intermediates, rationalizing the origin of stereochemistry.

An organocatalytic approach to 2-hydroxyalkyl- and 2-aminoalkyl furanes.

The first enantioselective methodology for the synthesis of electron-poor 2-hydroxyalkyl- and 2-aminoalkyl furanes is demonstrated in this study. It utilizes a highly stereoselective organocatalytic one-pot reaction cascade: epoxidation or aziridination of α,ß-unsaturated aldehydes followed by Feist-Bénary reaction of various 1,3-dicarbonyl compounds to give the target furanes. This efficient multibond forming reaction cascade benefits from low catalyst loadings and readily available starting materials. Furthermore, the possibility to interrupt the reaction sequence at the stage of the corresponding optically active 2-hydroxyalkyl- and 2-aminoalkyl 2,3-dihydrofuranes with three stereogenic centers is also presented. Finally, models which account for the formation of the optically active 2,3-dihydrofuranes are proposed.

Asymmetric formal trans-dihydroxylation and trans-aminohydroxylation of alpha,beta-unsaturated aldehydes via an organocatalytic reaction cascade.

This study demonstrates the first formal asymmetric trans-dihydroxylation and trans-aminohydroxylation of alpha,beta-unsaturated aldehydes in an organocatalytic multibond forming one-pot reaction cascade. This efficient process converts alpha,beta-unsaturated aldehydes into optically active trans-2,3-dihydroxyaldehydes and trans-3-amino-2-hydroxyaldehydes with the aldehyde moiety protected as an acetal. The elaborated one-pot protocol proceeds via the formation of 2,3-epoxy and 2,3-aziridine aldehyde intermediates, which subsequently participate in a novel NaOMe-initiated rearrangement reaction leading to the formation of acetal protected trans-2,3-dihydroxyaldehydes and trans-3-amino-2-hydroxyaldehydes in a highly stereoselective manner. Advantageously, this multibond forming reaction cascade can be performed one-pot, thereby minimizing the number of manual operations and purification procedures required to obtain the products. Additionally, for the purpose of trans-aminohydroxylation of the alpha,beta-unsaturated aldehydes, a new enantioselective aziridination protocol using 4-methyl-N-(tosyloxy)benzenesulfonamide as the nitrogen source has been developed. The mechanism of the formal trans-dihydroxylation and trans-aminohydroxylation of alpha,beta-unsaturated aldehydes is elucidated by various investigations including isotopic labeling studies. Finally, the products obtained were applied in the synthesis of numerous important molecules.

P-Chiral ferrocenephospholanes: synthesis, reactivity, metal complex chemistry and application in the asymmetric hydrogenation of olefins.

Starting from (R)-N,N-dimethyl-1-ferrocenylethylamine, a diastereoselective ortho-lithiation procedure and a stereoconvergent intramolecular hydrophosphination gave access to P-chiral ferrocenephospholanes. These mono- or bidentate ligands were converted to the corresponding rhodium and iridium complexes, including a chiral version of Crabtree's catalyst, and tested in the asymmetric hydrogenation of functionalized and unfunctionalized olefins. A significant reactivity difference between the rhodium-1,5-cyclooctadiene and the rhodium-norbornadiene complex was observed during catalyst activation.

Mechanisms in aminocatalysis.

The mechanisms of the α-, ß- and γ-functionalisations of aldehydes and α,ß-unsaturated aldehydes by secondary amines are presented and discussed.

Organocatalytic preparation of simple ß-hydroxy and ß-amino esters: low catalyst loadings and gram-scale synthesis.

A combined amino- and N-heterocyclic carbene (NHC)-catalyzed one-pot reaction sequence for the synthesis of simple enantioenriched ß-hydroxy and ß-amino esters using commercially available catalysts at low catalyst loadings has been developed. The desired products were obtained in high yield and excellent enantiopurity. The generation of quaternary stereocenters and application in gram-scale synthesis were also realized, with no requirements of inert or anhydrous reaction conditions, thus making this transformation a highly practical protocol.