Metal-free tetra-n-butylammonium bromide-mediated aerobic oxidative synthesis of β-ketosulfones from styrenes

An efficient and broadly applicable protocol for the aerobic coupling of styrenes with sulfonylhydrazides has been developed that affords P-ketosulfones bearing various functional groups in moderate to excellent yields.The preliminary experimental results support the involvement of active benzyl radical species,and a radical pathway was therefore proposed for the reaction.     

A facile stereospecific synthesis of chiral β-keto sulfoxides

A synthetic strategy has been devised for the preparation of chiral β-keto sulfoxides (actually, α-vinylsulfinyl ketones) starting from the readily available C-6 substituted 2,3-dihydro-1,4-oxathiines. The procedure, which is characterized by high yields and excellent enantiomeric excesses, represents an improvement in preparation methods for chiral β-keto sulfoxides.     

Copper catalyzed one-pot synthesis of β-ketophosphine oxides from ketones and H-phosphine oxides

A facile and efficient copper catalyzed one-pot method has been developed for the formation of β-ketophosphine oxides from ketones and H-phosphine oxides under air at room temperature, in which vinylhydrazinedicarboxylate was formed as the key intermediate. Preliminary mechanistic studies indicated that the reaction might involve a radical process and carbonyl oxygen atom of β-ketophosphine oxides came from molecular oxygen.     

PMA-SiO2 catalyzed synthesis of β-keto enol ethers

An efficient conversion of β-diketones into correspondingβ-keto enol ethers with catalytic amount of PMA-SiO_2 has been achieved.     

Metal-free synthesis of amphiphilic functional polycarbonates

Amphiphilic block copolymers of poly(5-benzyloxy trimethylene carbonate)(PBTMC) and poly(ethylene glycol)(PEG) were synthesized through enzymatic polymerization using immobilized porcine pancreas lipase(IPPL).The obtained copolymers with different compositions were characterized by GPC and ~1H NMR.The copolymer composition was in agreement with the feed ratio. The molecular weight of the copolymers showed an increasing trend with the decrease of PEG contents.Micelles of the copolymers were formed by dialysis procedure,and characterized by transmission electron microscopy (TEM).     

A facile synthesis of α-aminophosphonates catalyzed by ytterbium perfluorooctanoate under solvent-free conditions

Three-component reactions of aldehydes, amines and diethyl phosphite are efficiently catalyzed by ytterbium perfluorooctanoate [Yb(PFO)₃] under solvent-free conditions, giving the corresponding α-aminophosphonates in good to excellent yields. The catalyst can be recovered and reused for several times without any significant loss of activity. Furthermore, a possible mechanism for this transformation is also presented.     

On the synthesis of β-keto-1,3-dithianes from conjugated ynones catalyzed by magnesium oxide

MgO was used for the first time as a heterogeneous basic catalyst to synthesize β-keto-1,3-dithianes, potentially useful synthetic intermediates, from conjugated ynones and ynoates.     

A facile synthesis of trisubstituted alkenes from β-diketones and aldehydes with AlCl3 as catalyst

Preparation of trisubstituted alkenes from low-activity β-diketones and aldehydes with aluminum chloride as catalyst has been studied. The frequently used catalyst AlCl₃ is used for the first time to promote this condensation. The procedure is a convenient, low toxicity, and highly efficient method for industrial synthesis of trisubstituted alkenes in high yield.     

A facile synthesis of pyrano[2,3-d:6,5-d′]dipyrimidines via microwave-assisted multicomponent reactions catalyzed by β-cyclodextrin

A facile three-component reaction of aromatic aldehyde, 2,2-dimethyl-1,3-dioxane-4,6-dione, and 6-amino-1,3-dimethyluracil was developed for the first time using β-cyclodextrin (β-CD) as a macrocyclic host for aldehyde and an efficient catalyst that leads to a batch of novel pyrano[2,3-d:6,5-d′]dipyrimidines ( 4a-k ). The synthesis was accomplished with the aid of microwave irradiations in solvent-free conditions. The product obtained was in contrast to the previous report in which a similar reaction resulted in a mixture of benzylidenepyrimidine and bisaminopyrimidine analogs in the presence of triethylbenzylammonium chloride in an aqueous medium. The formation of the pyrano[2,3-d:6,5-d′]dipyrimidines may be in virtue of the property of β-CD to construct new C C and C X (where X = heteroatom) bonds. Reusability of the catalyst up to three runs without any noteworthy change in catalytic activity is one of the main features of the reaction. Other noteworthy features are good to excellent yields, eco-friendly procedure, non-column chromatographic purification, and mild conditions.     

Chiral phosphoric acid catalyzed enantioselective synthesis of β-amino-α,α-difluoro carbonyl compounds

A biphenol-based chiral phosphoric acid bearing a 9-anthryl group at each of the 3,3'-positions catalyzed the asymmetric Mannich-type reaction of N-Boc imine with difluoroenol silyl ethers in the presence of MS3A in THF to afford β-amino-α,α-difluoroketones in good yields and with excellent enantioselectivities. Optically pure 3,3-difluoroazetidin-2-one was readily synthesized from the Mannich-adduct.     

A facile method for the synthesis of enantiopure α-unsubstituted β-hydroxy esters

One-pot deacylation–debromination reactions involving the transesterification of the initial chiral α-bromo-β-hydroxy thioimide aldol adducts and subsequent Al–Hg mediated reductive cleavage of the C–Br bond allow for a facile synthesis of enantiopure β-hydroxy esters.     

Enantioselective synthesis of C2-symmetric hexols from β,δ-diketosulfoxides

An enantioselective synthesis of (1,2S,4S,8S,10S,11)-hexahydroxyundecane, a C₂-symmetric hexol precursor of the alkaloid (−)-lythranidine, is described. This convergent synthesis was based on the stereoselective reduction of two different β,δ-diketosulfoxides.     

An efficient reduction protocol for the synthesis of β-hydroxycarbamates from β-nitro alcohols in one pot: a facile synthesis of (−)-β-conhydrine

An efficient and practical one-pot protocol for the reduction of β-nitro alcohols to their corresponding N-(tert-butoxycarbonyl) amino alcohols using Zn-NH₄Cl in aqueous methanol is described. Other reducible groups such as ketones and isolated double bonds remained intact. This methodology allows a short synthesis of (−)-β-conhydrine to be achieved.     

A one-step procedure for facile, selective synthesis of protected d-glucopyranosides with free 2-C hydroxyl group starting from peracetylated β-D-glucopyranose

An important field in carbohydrate chemistry is to look for regioselective re-actions of saccharides to simplify the chemical synthesis of oligosaccharides. Oneof such efforts nowadays is directed to the convenient preparation of protected D-     

A facile synthesis and crystallographic analysis of N-protected β-amino alcohols and short peptaibols

A facile, efficient and racemization-free method for the synthesis of N-protected β-amino alcohols and peptaibols using N-hydroxysuccinimide active esters is described. Using this method, dipeptide, tripeptide and pentapeptide alcohols were isolated in high yields. The conformations in crystals of β-amino alcohol, dipeptide and tripeptide alcohols were analysed, with a well-defined type III β-turn being observed in the tripeptide alcohol crystals. This method is found to be compatible with Fmoc-, Boc- and other side-chain protecting groups.     

SmI_2-promoted imino-Reformatsky reaction for facile synthesis of enantioenriched β-amino acid esters

A facile and efficient method for the stereoselective synthesis of β-amino acid esters via SmI2-promoted imino-Reformatsky reaction is described.Asymmetric addition of tert-butyl bromoacetate to N-tert-butanesulfinyl aldimines afforded β-amino acid esters in moderate to high yields with excellent diastereoselectivities.The synthetic utilities of the tert-butyl β-amino acid esters were expanded by the preparation of β-lactams and 3-aminoindan-1-ones derivatives.     

Metal-free and highly regioselective synthesis of N-heteroaryl substituted pyrazoles from α,β-unsaturated N-tosylhydrazones and heteroaryl chlorides

A cascade cyclization/nucleophilic aromatic substitution (S_NAr) reaction of α,β-unsaturated N-tosylhydrazones with N-heteroaryl chlorides was developed for the synthesis of N-heteroaryl pyrazole derivatives. This one-pot reaction provided bi(heteroaryl) derivatives in good to excellent yields and with excellent regioselectivity. The procedure is operationally simple and applicable to large-scale synthesis.     

A facile synthesis of α,α′-bis(substituted benzylidene) cycloalkanones catalyzed by p-TSA under solvent-free conditions

Abstract

Various 2,6-dibenzylidene cycloalkanones were readily prepared in a few minutes with good yields by simply mixing aromatic aldehydes with cycloalkanones in the presence of catalytic amounts of p-toluenesulfonic acid as a solid heterogeneous catalyst under solvent-free condition.