Enantioselective α-amination of branched aldehydes promoted by simple chiral primary amino acids

A series of simple chiral primary amino acids were first successfully applied to promote the enantioselective α-amination of branched aldehydes with azadicarboxylates and the desired adducts bearing quaternary stereogenic centers were obtained in excellent yields (up to 99%) and enantioselectivities (up to 97% ee).     

Organocatalytic oxy-Michael addition of alcohols to α,β-unsaturated aldehydes

1,4-Addition of alcohols to α,β-unsaturated aldehydes was found to be efficiently promoted by biphenyldiamine-based catalyst 3 without formation of the acetals.     

A remarkably simple α-oximation of aldehydes via organo-SOMO catalysis

A novel α-oximation reaction of unactivated aldehydes has been achieved in excellent yields by reaction with NaNO(2)-FeCl(3) couple and in the presence of pyrrolidine as organocatalyst.     

The asymmetric hydroboration of simple alkenylsilanes: chiral α-silylalkyl- boranes and alcohols

The detailed study of the asymmetric hydroboration of various vinyl-silanes with monoisopinocampheylborane ( IPCBH₂) is presented. In all cases, β-substitution on the vinylsilane gives monomeric dialkylborane adducts with the boryl group α to the silicon. These studies show that the larger the groups on silicon are, the more positive the influence on the enantioselectivity of the process. Moderate asymmetric induction (24–40%) is observed only for vinyl-silanes which contain a substituent trans to the silicon. A model for the asymmetric hydroboration of alkenes with this reagent is proposed. The complete characterization of the borane intermediates was achieved employing NMR ( ¹¹B, ¹³C, ¹H, ²⁹Si).     

The acid free asymmetric intermolecular α-alkylation of aldehydes in fluorinated alcohols

The acid free asymmetric intermolecular α-alkylation of aldehydes with alcohols has been discovered using trifluoroethanol as solvent. This unprecedented system affords the enantioenriched functionalized primary alcohols (after NaBH(4) reduction) in high yields and good to excellent enantioselectivities with wide substrate scope in the absence of any acid additive.     

Asymmetric organocatalytic oxy-Michael addition of alcohols to α,β-unsaturated aldehydes

A 1,4-addition of alcohols to α,β-unsaturated aldehydes was found to be efficiently promoted by biphenyldiamine-based catalyst 3 without formation of the acetals. An asymmetric variant of this reaction has also been performed by designing a novel axially chiral organocatalyst (R)-10c.     

Synthesis of polyfunctionalized pyrroles bearing C-2 α-azido side-chains and displacement of the α-azido group by various nucleophiles

Tetrasubstituted pyrroles bearing C-2 α-azido side-chains were synthesized employing a new class of diazides, α,γ-diazido α,β-unsaturated esters, and 1,3-dicarbonyl compounds under simple thermal conditions. Further investigation of the synthetic utility of the obtained pyrroles reveals unexpected displacement of the α-azido group at the C-2 side-chain by a variety of nucleophiles. This two-step process exhibits a broad substrate scope, good functional group tolerance, simple operation, and high reaction efficiency, providing an easy access to polyfunctional pyrroles with novel substitution patterns.     

Asymmetric hydroazidation of α-substituted vinyl ketones catalyzed by chiral primary amine

We report herein the first example of asymmetric hydroazidation of α-substituted vinyl ketones by using chiral primary amines as the catalysts.A simple chiral primary-tertiary diamine catalyst derived from lphenylalanine was found to readily promote this aza-Michael addition reaction with enamine protonation as the key stereogenic step,thus enabling the effective synthesis of α-chiral β-azido ketones with good yields and moderate enantioselectivities.     

Preparation of novel multifunctional amino alcohols from nitroparaffins and α,β-unsaturated aldehydes

A series of novel multifunctional amino alcohols were prepared by tandem Michael–Henry reaction by reacting nitroalkanes such as 2-nitropropane with readily available α,β-unsaturated aldehydes. The dinitro compounds were further reduced by catalytic hydrogenation to obtain respective diamines. This synthetic route provides a very convenient method of preparing multifunctional amino alcohols.     

Facile synthesis of α-monofluoromethyl alcohols: Nucleophilic monofluoromethylation of aldehydes using TMSCF(SO2Ph)2

α-Fluoromethyl phenyl sulfone derivatives have been extensively employed in various reactions as versatile fluoromethylating reagents. While nucleophilic monofluoromethylations of aldehydes have been achieved using fluoromethyl phenyl sulfone or fluorobis(sulfonyl)methanes, a facile protocol under mild reaction conditions remains an ardently sought goal. We now report a feasible synthetic approach toward β-monofluorinated alcohols using α-trimethylsilyl-α-fluorobis(phenylsulfonyl)methane [TMSCF(SO₂Ph)₂, TFBSM] as a novel monofluoromethylating reagent. Initiated by a catalytic amount of fluoride, the reagent can be readily added to a variety of aldehydes providing the desired products in high yields. Computational and kinetic studies have revealed the exceptional lability of the Si–C bond in TFBSM compared with other fluoromethylsilane counterparts.     

Trimerization of aldehydes with one α-hydrogen catalyzed by sodium hydroxide

Trimerization of 2-methylpropanal (isobutyraldehyde) is a simple and effective method to synthesize 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and 2,2,4-trimethyl-1,3-pentanediol-3-monoisobutyrate which are often used as film forming auxiliaries in paints. The use of solid sodium hydroxide as a catalyst provides an excellent yield of above 85 % after the optimization of the reaction time and the catalyst dosage. Furthermore, trimerization of four other aldehydes with one α-hydrogen catalyzed by solid sodium hydroxide can also take place and the yield of 1,3-diol monoesters reaches 50–70 %. Trimerization of aldehydes with one α-hydrogen can be explained by a three-step reaction mechanism: (i) aldol condensation of aldehyde; (ii) crossed Cannizzaro reaction; and (iii) esterification of carboxylic acid and alcohol.     

Asymmetric synthesis of vicinal amino alcohols via organocatalytic sequential α-amination/Grignard addition reactions of aldehydes

An organocatalytic sequential α-amination/Grignard addition reaction of aliphatic aldehydes is reported. The synthetically useful anti-vicinal amino alcohol derivatives were obtained in high yields and with high stereoselectivities. These derivatives could be easily transformed into oxazolidinones.     

Pyridylmagnesiates: generation by bromine–metal exchange and enantioselective addition to aldehydes

Butyl and dibutylmagnesiates incorporating chiral ligands have been prepared and their reactivity studied. The reagents were efficient to promote the clean bromine–magnesium exchange of azinyl bromides at room temperature and subsequent reaction with aldehydes affording pyridylcarbinols. (R,R)-TADDOL-based dibutylmagnesiate was the best reagent leading to acceptable to good enantioselectivities, depending on the substrate and on the aldehyde substitution. This is the first example of enantioselective addition of in situ generated pyridylmagnesiate to carbonyl electrophiles.     

Enantioselective addition of Et_2Zn to aldehydes catalyzed by chi-ral aliphatic β-amino alcohols

This paper describes the preparation of two new optically active aliphatic β-amino alcohols (R)-5,5-dimethyl-2-(dimethy-lamino)-1,1-diphenyl-1-hexanol (1a) and (S)-8,8-dimethyl-2-(dimethylamino)-1, 1-diphenyl-1-nonanol (1b). They were synthesized by methylation of the corresponding β-amino alcohols 2a and 2b. Compounds la and 1b catalyze the addition of diethylzinc to various aldehydes enantioselectively. The catalyst structure-enantioselectivity relationships were discussed.     

Kinetic profiling of prolinate-catalyzed α-amination of aldehydes

Deconvolution of the role of off-cycle species from the desired catalytic cycle leads to an optimized protocol for the prolinate-catalyzed amination of aldehydes. The scope of complex reaction networks will be greatly broadened by understanding ancillary rate processes that influence the productive catalytic pathway.