Liquid-Phase Synthesis of Methyl (2Z)-2-Arylsulfonylmethyl-2- alkenoates from PEG-Supported α-Phenylselenopropionate

Treatment of lithio derivative of novel PEG-supported a-phenylselenopropionate with aldehydes, followed by oxidation-elimination with 30% hydrogen peroxide, formed Baylis-Hillman products, which were then reacted with sodium arylsulfinate. The resulting sulfonylated products were cleaved from the PEG efficiently affording methyl (2Z)-2-arylsulfonylmethyl-2-alkenoates in good yields and high purities.     

On the properties of the anions derived from α-deprotonation of α-(o-carboran-1-yl)- and α-ferrocenyl-1-alkylbenzotriazoles

The synthesis of 1-[(2-R-o-carboran-1-yl)methyl]benzotriazoles (R = Me, Ph) is described. α-Deprotonation of these compounds followed by reactions of the generated carbanions with MeI give the corresponding α-methylated products. Even at room temperature, they exist in solution as an equilibrium mixture of two conformers due to steric crowding around the C^α atom. In contrast, the anions generated by deprotonation of α-ferrocenyl derivatives of 1-methyl- and 1-ethylbenzotriazoles are ambident and are attacked by electrophiles at both the C^α and N(3) atoms.     

Carbonyl ylide formation from the rhodium (II) acetate catalyzed reaction of a α-diazoketone

Reaction of the α-diazoketone derived from 7-carboxyphthalide with rhodium acetate results in an internal cyclization to give a six-ring carbonyl ylide which is subsequently converted to 7-carbomethoxyphthalide.     

Stereochemistry of α-(tert-butoxycarbonylamino) hydroxylamines: 1H NMR analysis of hydroxylamines derived from 2-pyrrolidinyl nitrones

Hydroxylamines derived from 2-pyrrolidinyl nitrones can be easily and unambiguously distinguished by ¹H NMR spectroscopy. A strong hydrogen bond which can be observed both in the solid state and solution is responsible for the preferred conformation of the title compounds.     

Synthesis of α-amino acids using transition metal catalysis - alkylation of schiff bases derived from α-amimo acid esters (regio,stereo - selectivity)

A general approach to the synthesis of γ,δ-unsaturated α-amino acid esters is described. Schiff bases derived from glycine and alanine esters were alkylated in the presence of palladium or molybdenum catalysts under neutral or basic conditions using allylic carbonates, esters or halides, (20–95% yield). These less stabilized nucleophiles reacted with the η³ allyl species on the side opposite to the palladium and they can be classified as soft nucleophiles. The regioselectivity was studied with various unsymmetrical electrophiles. After hydrolysis, several functionalized α-amino acids of biological interest (enzymes inhibitors) were obtained. Asymmetric palladium allylic alkylation of the benzophenone imine glycine methyl ester using Pd(OAc)₂ + (+)DIOP was achieved with up to 68 % ee ; the enantioselective Pd-promoted alkylation of this new and useful prochiral nucleophile for the synthesis of α-amino acids is one of the highest ee known.     

1,3-Dipolar cycloaddition of a nitrone derived from (S)-malic acid to α,β-unsaturated δ-lactones

1,3-Dipolar cycloaddition of nitrone 7 to α,β-unsaturated δ-lactones: non-chiral 2, racemic mixture 3/3ent, d-glycero 3 and d-threo 15 proceeds with high stereoselectivity in the case of 2 and 15, and with a significant kinetic resolution in the case of the racemate 3/3ent. The endo approach of reactants was not observed. CD-spectroscopy proved an attractive tool for determination of the absolute configuration of cycloadducts.     

Further enantioselective syntheses of α-arylalkanamines via intermediate addition of Grignard reagents to a chiral hydrazone derived from (R)-(−)-2-aminobutan-1-ol

Reaction of various aromatic aldehydes with the chiral hydrazine (R)-(−)-2, derived from 2-aminobutan-1-ol (R)-(−)-1, gave the corresponding hydrazones 5–12. Enantioselective addition of EtMgBr or n-BuMgBr to 5–8 gave the trisubstituted hydrazines 13a–f (d.e.s=100%). Catalytic hydrogenolysis (6 bar/Pd–C/110°C/5 h) of the N–N bond of the latter afforded the enantiomerically enriched α-arylalkanamines (R)-(+)-14a–f (e.e.s=90–93%).     

Deracemisation of α-amino acids—(R)- and (S)-phenylalanine from the same enantiomer of a homochiral auxiliary

Chiral auxiliary (3S)-N,N′-bis-(p-methoxybenzyl)-3-isopropylpiperazine-2,5-dione 1 was employed for the synthesis of both enantiomers of phenylalanine using a regioselective deprotonation/stereoselective reprotonation strategy. Modification of this approach enables the efficient deracemisation of (±)-phenylalanine.     

Enantioselective syntheses of α-phenylalkanamines via intermediate addition of Grignard reagents to chiral hydrazones derived from (R)-(−)-2-aminobutan-1-ol

The hydrazine (R)-(−)-28 was obtained in four steps from 2-aminobutan-1-ol (R)-(−)-11, and reacted with benzaldehyde to give the hydrazone (R)-(−)-29. Nucleophilic addition of various alkyl Grignard reagents to the latter yielded the corresponding trisubstituted hydrazines (R,R)-30a–g in 70–89% yields and having d.e.s=100% (¹H and ¹³C NMR). Catalytic hydrogenolysis of these hydrazines afforded the corresponding (R)-(+)-α-phenylalkanamines (R)-(+)-31a–g having e.e.s=90–92% (chiral GPC).     

Reactions of α-imino ketones derived from arylglyoxals with (trifluoromethyl)trimethylsilane; a new route to β-amino-α-trifluoromethyl alcohols

The reactions of α-imino ketones, derived from arylglyoxals, with (trifluoromethyl)trimethylsilane (CF₃SiMe₃) in DME solution, in the presence of catalytic amount of CsF, at room temperature, yield O-silylated β-imino alcohols in the chemoselective manner. Subsequent reduction of these products with NaBH₄ in ethanolic solution leads to the corresponding β-(N-alkyl)amino-α-trifluoromethyl alcohols in good to excellent yields. Trifluoromethylation of enantiomerically pure α-imino ketones (with Ar = Ph or p-MeOC₆H₄), bearing as a chiral auxiliary the PhCH(Me) group attached to the nitrogen atom, yields mixtures of diastereomeric products in the ratio of ca. 3:2.     

Chiral Phosphine Ligands Derived from Sugars 4.Crystal Structure of Methyl 4,6-O-Benzylidene-3-Deoxy-3-(Diphenylphosphino)-α-D-Altropyranoside (3-MBPA)

IINTRODUCTIONChiralphosphinesareveryusefulligandsinenantioselectivecatalysiswithtransitionmetalcomplexes"'.Becausesugarisrichnotonlyinstereochemistrybutalsoinnatureandpossessesmanyhydroxylgroupsassyntheticstartingpoints,theyhavereceivedmuchattentionsincethe1970st2i.However,thetypesofchiralphosphinesinwhichthephosphorusatomsareattacheddirectlytothesecondarycarbonsofsugararefew.Thedifficultiesinthesyntheticprocessesarepartofthereason.Bythenucleophilicreplacementreaction,itisdifficulttolink…     

Synthesis and crystal structure of a trinuclear copper(II) complex derived from N,N′-Bis(4-methoxysalicylidene)-1,3-pentanediamine

A trinuclear copper(II) complex [Cu₃Cl₂L₂], where L is the dianionic form of N,N′-bis(4-methoxysalicylidene)-1,3-pentanediamine, has been synthesized and characterized by means of spectroscopic methods and single crystal X-ray structure determination. The complex crystallizes in the orthorhombic space group Pnma with unit cell dimensions a = 15.301(2), b = 23.226(2), c = 12.089(1)Å, V = 4296.2(8) ų, Z = 4, R ₁ = 0.0682, and wR ₂ = 0.1590. The molecule of the complex possesses a crystallographic mirror plane symmetry with the mirror plane passes through the three Cu atoms and the two Cl atoms. The two terminal Cu atoms adopt distorted square pyramidal coordination, and the middle one adopts square planar coordination. The intramolecular Cu…Cu distances are 2.900(1) and 2.916(1) Å. The complex was tested for its antibacterial activity to assess its inhibiting potential.     

Direct benzylic functionalization of pyridines:Palladium-catalyzed mono-α-arylation of α-(2-pyridinyl)acetates with heteroaryl halides

Herein,we report a Pd-catalyzed mono-a-arylation reaction for pyridine benzylic functionalization.This approach serves as an efficient alternative to synthesize di-heteroaryl acetates in good yields and selectivities.Moreover,the method is applicable to heteroa ryl substrate combinations,and exhibits great functional group tolerance.A streamlined protocol also enables the rapid synthesis of diheteroaryl ketones.The synthetic value was also demonstrated by scale-up experiments.     

Synthesis and Characterization of a Sb(Ⅲ)Complex with α-Diimine Ligand and a Csp3-Csp3 Coupling Production of the Original Ligand

A Csp3-Csp3 coupling production of the original ligand molecule [(CMeN(2,6-iPr2C6H3))2]2 (1) and an antimony ionic compound with α-diimine ligand [LH3]+[SbCl4]-(2, L = [(2,6-iPrC6H3)NC(Me)]2) were synthesized and characterized by 1H NMR, elemental analysis and single-crystal X-ray structural analysis. The crystal of compound 1 belongs to the orthorhombic system, space group Pbca with a = 21.173(4), b = 10.1639(17), c = 22.954(4) , V = 4939.8(14) 3, C56H78N4, Mr = 807.22, Z = 4, Dc = 1.085 g/cm3, μ(MoKα) = 0.062 mm-1, F(000) = 1768, S = 0.998, the final R = 0.0593 and wR = 0.1616 for 6481 observed reflections (Ⅰ > 2σ(Ⅰ)) and R = 0.0819 and wR = 0.1805 for all 28753 data. The crystal of compound 2 belongs to the triclinic system, space group P with a = 10.930(2), b = 12.553(2), c = 12.561(3) , α = 89.780(7), β = 82.861(6), γ = 68.598(4)o, V = 1590.5(5) 3, C28H43Cl4N2Sb, Mr = 671.19, Z = 2, Dc = 1.401 g/cm3, μ(MoKα) = 1.222mm-1, F(000) = 688, S = 0.989, the final R = 0.0294 and wR = 0.0616 for 7578 observed reflections (Ⅰ > 2σ(Ⅰ)) and R = 0.0366 and wR = 0.0639 for all 16515 data. Complex 1 can be rationalized as a result of Csp3-Csp3 coupling of two ligand molecules. The reaction of corres- ponding potassium salts with Sb(Ⅲ) chloride resulted in the antimony complex 2, in which the cationic moiety [LH3]+ is balanced by the presence of [SbCl4]- anion.     

The preparation of (-)-grandisine B from (+)-grandisine D; a biomimetic total synthesis or formation of an isolation artefact?

An efficient new alkyne-acetal cyclization procedure has been developed to prepare enantiopure indolizidine building blocks from l-proline and then applied to prepare the Elaeocarpus-derived alkaloids grandisine B and grandisine D in an efficient manner. However, evidence is presented which indicates that grandisine B does not occur naturally but is formed by reaction of grandisine D with ammonia during the extraction/purification process.     

Synthesis and crystal structure of a novel tri-nuclear nickel(II) complex derived from N,N′-(2-hydroxypropane-1,3-diyl)bis(salicylaldimine)

A novel tri-nuclear nickel(II) complex, [Ni₃L₂(μ₂-η¹:η¹-OAc)₂(μ₁-η¹:η⁰-OAc)₂] · H₂O (H₂L is N,N′-(2-hydroxypropane-1,3-diyl)-bis(salicylaldimine), was prepared. The complex was characterized by elemental analysis, IR spectra, and single crystal X-ray determination (CIF file CCDC no. 993163). Crystal of the complex crystallizes in the monoclinic space group P2₁/n. The unit cell parameters: a = 12.5602(9), b = 13.2104(10), c = 15.0329(10) Å, β = 113.194(2)°, V = 2292.7(3) ų, Z = 2, R ₁ = 0.0506, wR ₂ = 0.1342, S = 1.067. The complex possesses crystallographic inversion center symmetry. The Ni atoms are in octahedral coordination spheres. The Ni?Ni distances are 3.022(1) Å.     

Synthesis and Structure of a NovelTetranuclear Erbium( Ⅲ) Complex with α-Alanine [Er4(Hala)6·(μ3-OH)4(H2O)8](ClO4)8·3H2O

The title complex was synthesized in an aqueous solution and its crystal structure was determined by X-ray diffraction. The crystal crystallizes in a triclinic system, space group P1 with a=1.306 3(2) nm, b=1.319 4(4) nm, c=1.950 2(4) nm, α=90.597(14)°, β=93.998(11)°, γ=94.093(13)°, V=3.344 1(12) nm3, Z=2, the final R indices are R1=0.065 4, wR2=0.126 2 respectively. The complex contains a novel tetranuclear cluster cation with four Er3+ ions connected by four μ3-OH ions and six bridging carboxyl groups. Each erbium ion is coordinated by three μ3-OH, three carboxylic oxygen atoms from three α-alanine and two oxygen atoms from water molecules, forming a square-antiprismatic coordination polyhedron.     

Solid state conformations of α,β-unsaturated hydroxamates derived from the ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine

α,β-Unsaturated hydroxamates derived from the ‘chiral Weinreb amide’ auxiliary (S)-N-1-(1′-naphthyl)ethyl-O-tert-butylhydroxylamine consistently adopt a defined conformation and undergo highly diastereoselective conjugate addition reactions with lithium amide reagents. The configuration of the N-1-(1′-naphthyl)ethyl group dictates the position of the O-tert-butyl group and also the configuration adopted by the pyramidal nitrogen atom via a ‘chiral relay’ effect. Conjugate addition of lithium amide reagents to these substrates proceeds on the face opposite to both the O-tert-butyl group and nitrogen lone-pair with high levels of diastereoselectivity.     

Synthesis and Crystal Structure of α-( N-Protected a mino)β- lactam Derivative of 1 ,5-Benzothiazepine

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