Direct Organocatalytic Asymmetric α-Chlorination of Aldehydes

Asymmetric total synthesis of danicalipin A and evaluation of biological activity

Asymmetric total synthesis of danicalipin A was achieved. The synthesis was characterized by diastereoselective introduction of chlorine atoms. Biological activities with synthetic danicalipin A, its enantiomer, and racemate were also evaluated toward brine shrimp. Both enantiomers of danicalipin A showed almost the same activity.

Catalysis of phosphorus(V)-mediated transformations: dichlorination reactions of epoxides under Appel conditions

A stereospecific triphenylphosphine oxide-catalyzed 1,2-dichlorination reaction of epoxides has been developed. The reaction is effective for a range of terminal and internal epoxides. In contrast to the classical Appel-type dichlorination of epoxides, oxalyl chloride is used as a stoichiometric reagent to generate the chlorophosphonium salt responsible for dichlorination from catalytic triphenylphosphine oxide.

A concise and stereoselective synthesis of hydroxypyrrolidines: rapid synthesis of (+)-preussin

A convergent and stereoselective synthesis of 2,5-disubstituted 3-hydroxypyrrolidines has been developed that involves reductive annulation of β-iminochlorohydrins, which are readily available from β-ketochlorohydrins, and provides rapid access to a variety of 2,5-syn-pyrrolidines. Application of this process to the concise (three-step) synthesis of the fungal metabolite (+)-preussin and analogues of this substance is reported.

Stereoselective synthesis of chiral 4-(1-chloroalkyl)-beta-lactams starting from amino acids and their transformation into functionalized chiral azetidines and pyrrolidines

Chiral short-chain alpha-chloroaldehydes were prepared starting from enantiomerically pure amino acids in a three-step approach, thus providing a practical synthetic alternative for known organocatalytic alpha-chlorination procedures. The latter aldehydes proved to be useful starting materials for the stereoselective Staudinger synthesis of (3S,4S)-4-[(1S)-1-chloroalkyl]azetidin-2-ones in high diastereomeric ratios and good overall yields, which were used as chiral building blocks for the preparation of a number of azetidines and pyrrolidines.

Mechanisms in aminocatalysis

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

Regioselective and stereoselective cyclizations of chloropolyols in water: rapid synthesis of hydroxytetrahydrofurans

A concise, stereoselective synthesis of functionalized tetrahydrofuranols has been developed that involves heating readily available chloropolyols in water. These reactions are operationally straightforward and chemoselective for the formation of tetrahydrofurans, obviating the need for complicated protecting group strategies. The efficiency of this process is demonstrated in a short asymmetric synthesis of the natural product (+)-goniothalesdiol.

N-Heterocyclic carbene catalyzed asymmetric hydration: direct synthesis of alpha-protio and alpha-deuterio alpha-chloro and alpha-fluoro carboxylic acids

Asymmetric hydration of alpha,alpha-dichloro aldehydes and alpha-halo enals via a NHC-catalyzed redox process to yield enantioenriched alpha-chloro and alpha-fluoro carboxylic acids is described herein. The developed reaction allows for installation of an alpha-deuterium to give rise to enantioenriched alpha-deutero alpha-halo acids using D(2)O as the deuteron source.

Enantioselective α-Chlorination of Aldehydes with Recyclable Fluorous (S)-Pyrrolidine-Thiourea Bifunctional Organocatalyst

A novel fluorous (S)-pyrrolidine-thiourea bifunctional organocatalyst is prepared. The catalyst shows good activity and enantioselectivity for direct α-chlorination of aldehydes using N-chlorosuccinimide (NCS) as the chlorine source. It can be recovered from the reaction mixture by fluorous solid-phase extraction with excellent purity for direct reuse.

Enantioselective organocatalytic alpha-sulfenylation of substituted diketopiperazines

The asymmetric organocatalytic alpha-sulfenylation of substituted piperazine-2,5-diones is reported, with cinchona alkaloids as chiral Lewis bases and electrophilic sulfur transfer reagents. Catalyst loadings, the type of sulfur transfer reagent, temperature and solvent were investigated in order to optimize the reaction conditions. The effects of ring substitution and the type of catalyst on the yield and enantioselectivity of the reaction are reported.

Development of a concise and general enantioselective approach to 2,5-disubstituted-3-hydroxytetrahydrofurans

Concise syntheses of 2,5-disubstituted-3-hydroxytetrahydrofurans have been developed that provide access to each configurational isomer of this scaffold from a single aldol adduct. Application of these methods to the rapid preparation of (6S,7S,9S,10S)- and (6S,7S,9R,10R)-6,9-epoxynonadec-18-ene-7,10-diol, two structurally related marine epoxylipids, is reported.

Enantioselective linchpin catalysis by SOMO catalysis: an approach to the asymmetric alpha-chlorination of aldehydes and terminal epoxide formation

Time for SOme MOre: For the first time SOMO (singly occupied molecular orbital) activation has been exploited to allow a new approach to the alpha-chlorination of aldehydes. This transformation can be readily implemented as part of a linchpin catalysis approach to the enantioselective production of terminal epoxides.

Asymmetric, organocatalytic, three-step synthesis of gamma-hydroxy-(E)-alpha,beta-unsaturated sulfones and esters

Efficient and enantiocontrolled synthesis of gamma-hydroxy-alpha,beta-unsaturated sulfones and esters are reported through the reaction of enantioenriched alpha-selenyl aldehydes with EWG-stabilized carbanions and then a one-pot selenide oxidation, in situ epoxide formation, and final in situ epoxide opening.

Asymmetric aminocatalysis--gold rush in organic chemistry

Catalysis with chiral secondary amines (asymmetric aminocatalysis) has become a well-established and powerful synthetic tool for the chemo- and enantioselective functionalization of carbonyl compounds. In the last eight years alone, this field has grown at such an extraordinary pace that it is now recognized as an independent area of synthetic chemistry, where the goal is the preparation of any chiral molecule in an efficient, rapid, and stereoselective manner. This has been made possible by the impressive level of scientific competition and high quality research generated in this area. This Review describes this "Asymmetric Aminocatalysis Gold Rush" and charts the milestones in its development. As in all areas of science, progress depends on human effort.

Chiral NHC-catalyzed oxodiene Diels-Alder reactions with alpha-chloroaldehyde bisulfite salts

Alpha-chloroaldehyde bisulfite adducts were successfully employed in chiral NHC-catalyzed hetero-Diels-Alder reactions with various oxodienes under biphasic reaction conditions with high levels of enantioselectivity. This new protocol makes possible enantioselective additions from commercially available chloroacetaldehyde sodium bisulfite and demonstrates that this unique class of catalysts readily tolerates aqueous conditions.