Ultrasound-assisted rapid synthesis of β-cyanoepoxides using hypervalent iodine reagents

An elegant approach for the rapid synthesis of β-cyanoepoxides 3 by the epoxidation of β-cyanostyrenes 1 with PIDA 2a is described. The epoxidation of β-cyanostyrenes 1 was performed with 1.2 equiv. of PIDA 2a in MeCN-H₂O (1:1) at room temperature in ultrasonic bath. The epoxidation reactions were completed in short reaction time and β-cyanoepoxides 3 were isolated in 69–94% yields.     

Hypervalent organoiodine reagents in the β-fragmentation of bicyclic carbinolamides leading to imides

A mild and convenient method for the synthesis of 3,4-substituted cyclic imides by photolysis of bicyclic [3.3.0]- and [3.2.1]-carbinolamides in the presence of (diacetoxyiodo)-benzene and iodine is described.     

Bio-solvents change regioselectivity in the synthesis of disaccharides using Biolacta β-galactosidase

Bio-solvents are good alternative solvents that avoid the use of classical organic solvents when performing enzymatic reactions. A noticeably change in regioselectivity was observed in the synthetic behaviour of Biolacta β-galactosidase using bio-solvents derived from dimethylamide and glycerol as co-solvents. Under these conditions, the enzyme changes its well known tendency to produce β-(1→4) to β-(1→6) disaccharides. An evaluation of the bio-solvent concentration and the effects of the non proteic additives in commercially available Biolacta β-galactosidase was undertaken in order to optimize the reaction conditions to improve the yield of the β-(1→6) product.     

Transition-metal catalysis in michael addition of β-dicarbonyls : Tuning of the reaction conditions

(2,4- Pentanedionato) copper(I) and bis(2,4-pentanedionato)copper(II) together with boron trifluoride etherate catalyze Michael addition of β-dicarbonyls to cyclohexenone, cyclopentenone, 2-methylcyclopentenone, and 3-thienylidenemalonaldehyde.     

Aza-annulation of β-enaminolactones: application to the synthesis of enantiopure difunctionalized bicyclic lactams

Diastereoselective aza-annulation of seven-membered β-enaminolactones 2 gives access to bicyclic heterocyles 5. Fragmentation of molecule 5a with lithium methoxide affords cis or trans bicyclic lactams 8 with excellent stereoselectivities.     

Synthesis of β-ketophosphonates with electron rich β-aryl groups as useful organophosphorus reagents in lignans synthesis

Investigation of the oxidation reaction of electron rich alkoxy substituted β-aryl β-hydroxyphosphonates to corresponding β-ketophosphonates, which may be utilized in syntheses of lignans with various oxidizing agents (PCC, PDC, SIBX, CAN, Oxone^®, KMNO₄/SiO₂, KMnO₄/MS 4 Å, KMnO₄/CuSO₄, KMnO₄/CuSO₄/Al₂O₃, MnO₂, CrO₃/SiO₂, H₂O₂/salen) is described. The effect of oxidants and reaction conditions on the reaction efficiency and yield was also investigated.     

Enantioselective 1,4-addition of aryllithium reagents to α,β-unsaturated tert-butyl esters in the presence of chiral additives

Reaction of t-BuLi with a mixture of aryl bromide and chiral diamine, amino ether or diether, in toluene at −78°C provided chiral aryllithium complexes efficiently. Reaction of these aryllithium complexes with α,β-unsaturated tert-butyl esters afforded the 1,4-addition products in up to 88% ee.     

Ligand-controlled synthesis of vanadium(I) β-diketiminates and their catalysis in cyclotrimerization of alkynes

Three dimeric vanadium(I) β-diketiminates [V{μ-(η(6)-ArN)C(Me)CHC(Me)C(N-Ar)}](2) (Ar = 2,6-Me(2)C(6)H(3) (2), 2,6-Et(2)C(6)H(3) (3), 9-anthracenyl (4)) were prepared and isolated upon reduction of their corresponding dichloro precursors VCl(2)(Nacnac). Compounds 2-4 all show a structure with each vanadium atom being η(2) bonded to the β-diketiminate framework and η(6) bonded to a flanking ring of a β-diketiminato ligand, attached to the other vanadium centre within the dimer. No metal-metal bonding interactions are observed in these dimers due to long vanadium-vanadium separations. Compounds 2-4 display an antiferromagnetic exchange between the two vanadium centres. An imido azabutadienyl complex (η(2)-PhCC(H)C(Ph)NC(6)H(3)-2,6-(i)Pr(2))VN(C(6)H(3)-2,6-(i)Pr(2))(OEt(2)) (5) was isolated from the reduction of VCl(2)(HC(C(Ph)NC(6)H(3)-2,6-(i)Pr(2))(2)) by KC(8). Compounds 2-4 and the inverted-sandwich divanadium complex (μ-η(6):η(6)-C(6)H(5)Me)[V(HC(C(Me)NC(6)H(3)-2,6-(i)Pr(2))(2))](2) (1) reduce Ph(2)S(2) to give two vanadium dithiolates V(SPh)(2)[(HC(C(Me)NC(6)H(3)-2,6-R(2))(2))] (R = Et (6), (i)Pr (7)) through an oxidative addition. Most notably, 1 and 3 catalyze the cyclotrimerization of alkynes, giving tri-substituted benzenes in good yields and a 1,3,5-triphenylbenzene coordinated intermediate 8 was isolated and characterized.     

Regioselective addition of organomagnesium reagents to N-silyl activated nicotinic acid esters—a convenient method for the synthesis of 4,4-disubstituted 1,4-dihydronicotinates

The addition of RMgX or R₂Mg to nicotinic acid esters, activated with triisopropylsilyl triflate, was investigated. The regioselectivity of this reaction, where 4-unsubstituted and 4-substituted pyridine derivatives were employed as starting materials, was examined. Depending on the structure of the organomagnesium reagent varying ratios of 1,2-, 1,4-, and 1,6-regioisomers were obtained but in any case the 1,4-addition products were clearly predominating. Desilylation of the isomeric pure addition products with LiOH provided stable 4,4-disubstituted dihydropyridines, which could be easily N-alkylated with alkylhalides in high yield. Furthermore, it was shown that the silyl protecting group of the obtained dihydropyridines can be easily replaced by an acyl group.     

An approach to the Paal–Knorr pyrroles synthesis in the presence of β-cyclodextrin in aqueous media

An efficient and facile method for the synthesis of N-substituted pyrroles in moderate to good yields by the Paal–Knorr reaction of γ-diketones with amines in the presence of β-cyclodextrin in aqueous media has been developed.Moreover,this process tolerated diamines(e.g.,para-,meta- or orthophenylenediamine)to construct bis-pyrrole or mono-pyrrole derivates.β-Cyclodextrin can be recovered easily after the reactions and reused without evident loss in activity.     

The first organocatalytic addition of 2-trimethylsilyloxyfuran to carbonyl compounds: hydrogen-bond catalysis in γ-butenolides synthesis

This letter describes the first example of diastereoselective ‘organocatalyzed’ synthesis of the butenolide products substituted at the γ-position by a chain bearing hydroxyl groups. The urea-derivative 4 has proved to be an efficient catalyst for the addition of the commercial TMSOF to carbonyl compounds under solvent-free conditions. The reaction conditions and generality of the procedure have been examined.     

Stereoselective synthesis of conjugated all-trans-tetraenes. Application to the synthesis of β-parinaric acid methyl ester

in this paper is reported the stereoselective synthesis of all-trans-tetraenes by reductive elimination of 1,8-dibenzoate-2,4,6-trienes with sodium amalgam. The method was applied to the syntheses of 4E, 6E, 8E, 10E-heptatetraene and β—parinaric acid methyl ester.     

Dichotomy within 1,4-addition of organolithium and Grignard reagents to α,β-unsaturated Fischer alkoxycarbenes: A new synthesis of Fischer carbenes

The reaction of organolithium and Grignard reagents with pentacarbonyl[(ethoxy)(2-phenylethenyl)carbene]chromium(0) gave, after the quenching of the initially formed product of the 1,4-addition, different products depending on the organometallic and quenching reagents used. The addition of organolithiums, followed by a work-up with acid (AcOH or HCl), afforded the corresponding carbene complexes. In contrast, quenching the reaction mixture with ethanol led to the stereoselective formation of (Z)-enol ethers. The usage of Grignard reagents led to the formation of the carbene complexes regardless of which quenching reagent was used.     

A novel polycondensation method for the synthesis of a two-faced β-1,4-glucan

Abstract  

The stereospecific synthesis of a chitosan derivative repeating 2-azido-3,6-di-O-benzyl-2-deoxy-β-d-glucopyranosyl-(1 → 4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-d-glucopyranose, which has two distinguishing faces, was achieved by polycondensation of the sole starting disaccharide, trichloroacetimidoyl 2-azido-3,6-di-O-benzyl-2-deoxy-β-d-glucopyranosyl-(1 → 4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-d-glucopyranoside in a short and efficient way.     

Supramolecular biomimetic catalysis by β-cyclodextrin for the synthesis of new antimicrobial chromeno[4,3-b]quinolin-isonicotinamides in water

Research on Chemical Intermediates - Herein, a fast and convenient protocol for the synthesis of new isoniazid fused chromeno[4,3-b]quinolin was achieved through biomimetic catalysis by...     

A chemoenzymatic approach to the synthesis of the stereoisomers of a β-adrenergic receptor antagonist

The four stereoisomers of Δ²-isoxazoline 2, a β-adrenergic receptor antagonist structurally related to Falintolol 1, were prepared by an enzyme-catalyzed kinetic resolution of the unsaturated secondary alcohol (±)-7 followed by its cycloaddition to pyruvonitrile oxide. Through this strategy, diastereomeric aminoalcohols (+)-2a/(−)-2b and (−)-2a/(+)-2b were obtained in 99 and 92% enantiomeric excess, respectively. The absolute configuration to the target compounds was assigned via chemical correlation to the enantiomers of epoxides 4a and 4b, whose stereochemistry had been previously established.     

Asymmetric synthesis of β-substituted γ-lactams via rhodium/diene-catalyzed 1,4-additions: application to the synthesis of (R)-baclofen and (R)-rolipram

An efficient rhodium/diene-catalyzed asymmetric addition of arylboronic acids to α,β-unsaturated γ-lactams has been developed. The power of this methodology is further demonstrated by the concise synthesis of (R)-baclofen and (R)-rolipram.