Iridium-catalyzed enantioselective allylation of sodium 2-aminobenzenethiolate: an access to chiral benzo-fused N,S-heterocycles

The use of sodium 2-aminobenzenethiolate in the enantioselective iridium catalyzed allylic substitution with a range of methyl allyl carbonates allows the concise synthesis of the branch-type products with both excellent regio- and enantioselectivities, which are functionalized N,S-containing allylic intermediates for the formation of chiral benzo-fused N,S-heterocycles.     

Effects of allylic and homoallylic substituents on the ring closing metathesis reaction used to synthesise simplified eleuthesides

During the course of our synthetic studies towards simplified eleuthesides, we have found that p-methoxyphenyl (PMP) protected allylic alcohols are compatible with the RCM reaction and can give better yields than the corresponding free allylic alcohols.     

Selective aerobic oxidation of allylic and benzylic alcohols catalyzed by N-hydroxyindole and copper(I) chloride

In the presence of copper(I) chloride, tert-butyl 1-hydroxy-2-methyl-6-trifluoromethyl-1H-indole-3-carboxylate acted as a catalyst for the chemoselective aerobic oxidation of allylic and benzylic alcohols. A variety of primary and secondary allylic and benzylic alcohols were oxidized into the corresponding α,β-unsaturated carbonyl compounds in good yields without affecting non-allylic alcohols.     

Catalytic amination reactions mediated by Co(II) Schiff base complexes

Co(acacen), 1, (acacen = 2,11-dihydroxy-4,9-dimethyl-5,8-diaza-2,4,8,10-dodecatetraene dianion) was found to be a highly efficient catalyst for the allylic amination of non activated alkenes, using N-(p-toluensulfonyl)iminophenyliodinane (PhINTs) as nitrene precursor. This reactivity has been extended to the less reactive C-H bond of toluene. The effect of reaction times and of added cosolvent on yields and selectivities was investigated. Under the best conditions, allylic amines were obtained in a 40-70% isolated yield. A complex derived from the stoichiometric reaction of Co(acacen), 1, with PhINTs has been isolated and spectroscopically characterized. Such a complex, although not able to transfer its NTs moiety to alkenes, is still active in catalyzing allylic amination of cyclohexene.     

Regio- and stereoselective synthesis of Z-vinylic tellurides from propargylic alcohols: a route to chiral Z-enynes

tert-Butyldimethylsilyl ethers of propargylic alcohols are hydrotellurated regioselectively to give 1,2-Z-vinylic tellurides. Enantiomerically pure propargylic alcohols give enantiomerically pure vinylic tellurides, which are coupled with alkynes under Pd catalysis to give enantiomerically pure allylic enynols.     

Synthesis of chiral 2,2′-dipyridylamines and their use in the copper-catalyzed asymmetric allylic oxidation of cyclohexene

Chiral dipyridylamines have been synthesized by N-arylation reactions, and the applicability of those compounds to the copper-catalyzed asymmetric allylic oxidation of cyclohexene was demonstrated.     

E/Z Isomerization of 3,3-disubstituted allylic thioethers

Allylic thioethers of the general structure 1 underwent E/Z isomerization during both basic and acidic hydrolysis of the ester moiety at the remote end of the molecule. The isomerization was dependent on the substitution of the allylic moiety. The presence of a 5-membered heterocycle on the double bond supported the isomerization. However, analogous oxy-ethers were stable.     

Influence of structural changes in ferrocene phosphane aminophosphane ligands on their catalytic activity

New phosphane aminophosphane ligands based on [3]ferrocenophane skeleton were synthesized using a direct double lithiation followed by phosphanylation. Influence of ligand structure on catalytic performance was evaluated by performing a series of Pd-catalyzed allylic substitution on different substrates. Enantioselectivities up to 55% ee were obtained with bridged ligand compared to 33% ee with analogous non-bridged BoPhoz ligand.     

Regiocontrolled fluorination of 2-hydroxyalkyl dihydropyrans and carbonyl derivatives

Reaction of polysubstituted 2-hydroxyalkyldihydropyrans with DAST led regiospecifically to fluorination at the exocyclic position, except for primary alcohols. Difluorination of carbonylated analogues with deoxo-fluor™ occurred also regioselectively. The unexpected stability and synthetic potential of these new allylic fluorides are discussed.     

BINOL-derived N-phosphino sulfoximines as ligands for asymmetric catalysis

BINOL-derived N-phosphino sulfoximines have been prepared for the first time and tested as ligands in asymmetric transition metal catalysis. Up to 99% ee was achieved in the Rh-catalyzed asymmetric hydrogenation of functionalized olefins and up to 66% ee in the Pd-catalyzed allylic alkylation.     

Synthetic studies on bradykinin antagonist martinellines: construction of a pyrrolo[3,2-c]quinoline skeleton using silicon-tether RCM reaction and allylic amination

The pyrrolo[3,2-c]quinoline consisting of a core structure of martinellines, the first naturally occurring heterocycle, was prepared through silicon-tether ring-closing metathesis reaction and intramolecular allylic amination as key steps.     

γ-Selective allylic substitution reaction with Grignard reagents catalyzed by copper N-heterocyclic carbene complexes and its application to enantioselective synthesis

The reaction of allylic compounds with alkyl Grignard reagents in the presence of a catalytic amount of copper N-heterocyclic carbene (NHC) complexes proceeded predominantly in an S_N2′ reaction pathway to give γ-substituted product in excellent yield. The method was applied to asymmetric reaction by using optically active NHC ligands.     

Aza-Nazarov cyclization cascades

Benzamides with tethered acetal groups undergo reactions in CF₃SO₃H to give ring-fused isoindolinones by a cyclization cascade. The reaction initially forms an N-acyliminium ion which then gives the isoindolinone by the aza-Nazarov reaction. An unusual variant also cyclizes at the allylic position.     

A simple method for the oxidation of primary alcohols with o-iodoxybenzoic acid (IBX) in the presence of acetic acid

A simple method for the oxidation of primary alcohols to aldehydes using o-iodoxybenzoic acid (IBX) with the addition of stoichiometric acetic acid has been developed. Addition of acetic acid significantly accelerated the reaction rate. Under these conditions, primary aliphatic, benzylic, and allylic alcohols are smoothly converted to aldehydes in high yields (90-97%).     

Kinetic resolution of allylic alcohols via stereoselective acylation catalyzed by lipase PS-30

By using lipase PS-30 as catalyst, the kinetic resolution of a series of racemic allylic alcohols has been achieved via stereoselective acylation. The value of kinetic enantiomeric ratio (E) reached up to 968. Substituent effect is briefly discussed.     

N-Bromosuccinimide-mediated reaction of cyclic styrenes with chloramine-T

A facile route toward substituted allylic sulfonamides 3 is developed from the N-bromosuccinimide (NBS)-mediated allylic amination of cyclic styrenes 2 with chloramine-T (1a). Skeleton 2 is prepared by Grignard addition of cyclic ketones with different arylmagnesium bromides in THF followed by dehydration of the resulting tertiary alcohols with BF₃·OEt₂ in CH₂Cl₂. The synthetic route obtained moderate yields from the one-step operation and the key structures of skeleton 3 were confirmed by X-ray crystallographic analysis.     

Copper(I) tert-butoxide-promoted stereospecific alkylation of β-hydroxymethylvinylsilanes with alkyl halides

Stereospecific alkylation of (Z)-β-hydroxymethylvinylsilanes proceeded by treatment with copper(I) tert-butoxide and alkyl halides. Tri- and tetra-substituted allylic alcohols were obtained with complete retention of configuration.     

Palladium-catalysed allylic amination for the direct synthesis of epi-4-alkylamino-N-acetylneuraminic acid derivatives

A simple and efficient procedure has been developed for the direct formation of epi-4-alkylamino-N-acetylneuraminic acid derivatives as potential inhibitors of influenza neuraminidases. The allylic amination of oxazoline 6 has been effected with a series of primary and secondary amines in the presence of catalytic Pd(π-allyl)₂(Et₃P)₂ to give the corresponding 4-epi-alkylamino products in a stereoselective and regiospecific manner.     

Nickel-catalyzed coupling of terminal allenes, aldehydes, and silanes

The development of a nickel-catalyzed coupling of terminal allenes, aldehydes, and silanes is described. This transformation selectively provides 1,1-disubstituted allylic alcohols, protected as a silyl ether. The choice of the reducing agent is essential for achieving selectivity in this coupling process. A trialkylphosphine (Cyp₃P) and an N-heterocyclic carbene (IPr) are complementary in this reaction.     

Phosphine-catalyzed [3+3] annulation reaction of modified tert-butyl allylic carbonates and substituted alkylidenemalononitriles

A phosphine-catalyzed [3+3] annulation reaction of modified tert-butyl allylic carbonates with various alkylidenemalononitriles to form cyclohexenes was developed. The use of protic solvent is crucial in this reaction. When non-polar solvent, toluene or xylene, was used, only non-cyclized product was obtained.