Catalytic allylic oxidation with a recyclable, fluorous seleninic acid

In conjunction with iodoxybenzene as reoxidant perfluorooctylseleninic acid catalyzes the allylic oxidation of alkenes to enones in trifluoromethylbenzene at reflux in moderate to good yield. After a reductive workup with sodium metabisulfite, the catalyst is recovered by fluorous extraction in the form of bis(perfluorooctyl) diselenide, which, itself, serves as a convenient catalyst precursor. [reaction: see text]     

Catalytic asymmetric cyclopropanation of allylic alcohols with titanium-TADDOLate: scope of the cyclopropanation reaction.

A substoichiometric amount of titanium-TADDOLate complex was effective at catalyzing the cyclopropanation reaction of allylic alcohols in the presence 1 equiv of bis(iodomethyl)zinc. After initial optimization of the catalyst structure, excellent yields and enantiomeric ratios were obtained for 3-aryl- or 3-heteroaryl-substituted allylic alcohols (up to 97:3). Alkyl-substituted allylic alcohols gave modest yields and enantiomeric ratios (up to 87:13) but these compare favorably with those observed with other substoichiometric chiral ligands. The full synthetic scope of the reaction is presented in this paper.     

Direct, enantioselective iridium-catalyzed allylic amination of racemic allylic alcohols

The direct route: Iridium-catalyzed direct conversion of branched allylic alcohols into enantioenriched branched primary allylic amines is highly regio- and enantioselective (see scheme; coe=cyclooctene).     

Highly enantioselective Pd-catalyzed allylic alkylation of indoles using Sulfur-MOP ligand

The preparation of various (R)-Sulfur-MOP ligands with aryl and alkyl substituents on sulfur, and the application of these ligands to Pd-catalyzed asymmetric allylic alkylation of indoles is reported. The sulfur substituent served as an effective stereocontrol element, and in the case of the 2-i-PrPh substituent on sulfur, the allylation products from an array of simple and substituted indoles were obtained with high enantioselectivity (up to 95% ee).     

Liquid-phase synthesis of chiral tartrate ligand library for enantioselective sharpless epoxidation of allylic alcohols

This paper reports a successful development of a group of efficient soluble polymer-supported chiral tartrate ligands by liquid-phase synthesis for Sharpless epoxidation of a variety of allylic alcohols through ligand diversity. The influence of substituent in chiral tartrate ligands on the enantioselectivities of the reaction was disclosed. Moderate chemical yields and good enantiomeric excesses were obtained by using soluble polymer-supported tartrate ester in the epoxidation of allylic alcohols with Ti(O-i-Pr)(4)/tert-butyl hydroperoxide.     

Syntheses of (R)-(+)-cibenzoline and analogues via catalytic enantioselective cyclopropanation using (S)-phenylalanine-derived disulfonamide

Cyclopropanation of 3,3-diaryl-2-propen-1-ols 1 with Et₂Zn and CH₂I₂ proceeded in the presence of a catalytic amount of (S)-2-(methanesulfonyl)amino-1-(p-toluenesulfonyl)amino-3-phenylpropane 2 to afford the corresponding cyclopropylmethanols with 20–76% ee. (+)-2,2-Diphenylcyclopropylmethanol 3a (76% ee) was oxidized with IBX in DMSO, followed by NaClO₂, H₂O₂, and NaH₂PO₄ in MeCN–H₂O to give the corresponding acid 5a, which was converted with ethylenediamine, in the presence of PyBOP and Et₃N in CH₂Cl₂, to the amide 6a in quantitative overall yield from 3a. Amide 6a was cyclized at 160 °C under reduced pressure (2 mmHg) to afford (R)-(+)-cibenzoline in 55% yield.     

Oxazaborolidine-catalyzed enantioselective reduction of alpha-methylene ketones to allylic alcohols

Oxazaborolidine-catalyzed enantioselective reduction of alpha-methylene ketones was efficiently carried out by using borane-diethylaniline as a stoichiometric reducing agent. The combination of this method and subsequent hydrogenation of thus-formed allylic alcohol improved stereoselectivity in the reduction of 24-oxocholesteryl ester to 24-(R)-hydroxycholesteryl ester.     

Catalytic enantioselective synthesis of secondary allylic alcohols from terminal alkynes and aldehydes via 1-alkenylboron reagents

A practical one-pot method has been developed for preparing enantioenriched secondary allylic alcohols starting from terminal alkynes and aldehydes. Hydroboration of terminal alkynes with dicyclohexylborane and subsequent reaction of the resulting alkenylboron reagents with aldehydes in the presence of a catalytic amount (5 mol %) of 3-(3,5-diphenylphenyl)-H(8)-BINOL and excess titanium tetraisopropoxide afforded the corresponding allylic alcohols in high enantioselectivities up to 94% ee.     

Catalytic asymmetric reductive coupling of alkynes and aldehydes: enantioselective synthesis of allylic alcohols and alpha-hydroxy ketones

A highly enantioselective method for catalytic reductive coupling of alkynes and aldehydes is described. Allylic alcohols are afforded with complete E/Z selectivity, generally >95:5 regioselectivity, and in up to 96% ee. In conjunction with ozonolysis, this process is complementary to existing methods of enantioselective alpha-hydroxy ketone synthesis.     

An effective and catalytic oxidation using recyclable fluorous IBX

Oxidation of alcohols in the presence of a catalytic amount of fluorous IBX and Oxone as a co-oxidant resulted in the corresponding carbonyl compounds in good to high yields. The fluorous IBX is readily recovered as insoluble fluorous IBA from the reaction mixture by simple filtration, and can be reused without significant loss of the catalytic activity.     

Steric effects of the ligand in the enantioselective palladium-catalyzed allylic alkylation using chiral oxazolinylpyridines

Eight new chiral oxazolinylpyridines were prepared and assessed in the enantioselective palladium-catalyzed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate. Catalytic activity and enantioselectivity were found to be highly dependent upon the steric requirement of the substituent on the pyridine ring: enantioselectivity up to 92% has been obtained.     

Catalytic and enantioselective allylic C-H activation with donor-acceptor-substituted carbenoids

In this perspective we give an overview of enantioselective C-H activation at allylic sites by means of rhodium(II)-stabilized donor-acceptor-substituted carbenoids. This methodology has been proven to be both an equivalent to established asymmetric reaction sequences and a new synthetic approach with no established counterpart in organic synthesis.     

Synthesis of new fluorous modular chiral ligand derivatives from amino alcohols and application in enantioselective carbon–carbon bond-forming alkylation reactions

N-Trifluoracyl β-chalcogeno amides and N-perfluoracyl β-thio amide ligands were prepared by a simple and efficient reaction sequence. These new ligands were evaluated in palladium-catalyzed alkylation of rac-(E)-1,3-diphenyl-2-propenyl acetate in the presence of dimethyl malonate and an enantioselectivity of up to 99% was obtained. After catalysis, the fluorous ligand can be easily recovered by liquid–liquid extraction and reused without loss in the activity.     

Catalytic enantioselective synthesis of secondary alcohols using C2-symmetric diamino diol ligands

A new class of diamino diols was evaluated as catalytic ligands in the enantioselective borane reduction of aromatic ketones and the enantioselective ethylation of arylaldehydes with diethylzinc. By variation of the substitution pattern on the ketone, e.e.s of up to 94% could be obtained by in situ borane reduction using 0.025 equiv. of the ligand at 35°C in THF. N,N,N′,N′-Tetramethyldiamino diol and N,N′-dialkyl diamino diol were used as promoters for the enantioselective addition of diethylzinc reagent to the arylaldehyde, where use of 0.1 equiv. of N,N,N′,N′-tetramethyl diamino diol as catalyst in the addition of diethylzinc to arylaldehyde achieved e.e.s of up to 98%.