First synthesis of dialkyl phosphonate derivatives of sesquiterpene α-methylene-γ-lactone

The stereoselective synthesis of two phosphorus-containing derivatives of the known guaianolide arglabin was carried out for the first time. The molecular structures of these products were established based on the spectroscopic data and the results of X-ray diffraction analysis of one of these compounds.     

The reaction of α-phenethyl radicals with 1,4-benzoquinone and 2,6-di-tert-butyl-1,4-benzoquinone

The absolute rate constant for 1,4-benzoquinone (BQ) irreversibly trapping α-phenethyl radicals (3) has been determined as 4.4×10⁶ M⁻¹ s⁻¹ at 43 °C using acyclic cis azoalkane 9c as a radical precursor. These reactants afford the hydroquinone mono ether 4 at 30 °C but a mixture of products at elevated temperature. 2,6-Di-tert-butyl-1,4-benzoquinone (DTBQ) also reacts with 3 but the cyclohexadienone products are thermally labile.     

Synthesis of histidinoalanine: a comparison of β-lactone and sulfamidate electrophiles

Previous syntheses of histidinoalanine (HAL) have led to mixtures of regioisomers and/or stereoisomers. For example, opening of N-Cbz-D-serine-β-lactone (6) with Boc-L-His-OMe (5) gave a 2:1 mixture of τ- and π-regioisomers. The sulfamidate 10, derived from N-benzyl-D-serine methyl ester (11), was reacted with Boc-L-His-OMe (5) to give the τ-HAL derivative 17 as a single isomer in 57% yield. A similarly prepared τ-HAL 19, bearing protecting groups that were all hydrogenolytically labile, led to the free bis-amino acid, τ-L-histidinyl-D-alanine (τ-4), as a salt-free standard for amino acid analysis.     

Synthesis of new 1,4- and 1,5-disubstituted N-ethyl acetate and N-α-butyro-γ-lactone alkylimidazole derivatives as N-acylhomoserine lactone analogs

New alkylimidazoles functionalized with a homoserine lactone or an alkyloxycarbonyl moiety have been synthesized as N-acylhomoserine lactones (AHLs) analogs. The 1,4-disubstituted imidazole derivatives were prepared by alkylation of 4(5)-alkylimidazoles with α-bromo-γ-butyrolactone or ethyl α-bromoacetate. An alternative route was preferred for the synthesis of their 1,5-disubstituted counterparts based on the use of a N₁-protected alkylimidazole, its alkylation to an N₃-imidazolyl-α-acetate and deprotection to the desired 1,5-disubstituted esters and subsequent alkylation of the acetate moiety with cyclic ethylene sulfate followed by acid-catalyzed cyclization. The ability to modulate bacterial quorum sensing of all new compounds was compared to that of previously reported AHL analogs in which the amide bond is replaced by a heterocyclic group.     

High-yielding synthesis of 2-arylacrylamides via homogeneous catalytic aminocarbonylation of α-iodostyrene and α,α′-diiodo-1,4-divinylbenzene

Highly reactive iodoalkenes (α-iodostyrene and α,α′-diiodo-1,4-divinylbenzene) were prepared and used as substrates in palladium-catalysed aminocarbonylation reaction. Regardless of the type of amine nucleophile the corresponding N-substituted phenylacrylamides have been formed chemoselectively in nearly quantitative yields. High isolated yields (up to 83%) have been achieved both with unfunctionalised simple amines and amino acid methyl esters under mild reaction conditions.     

Synthesis of new α-hydroxyphosphonates and α-acetoxyphosphonates

A series of new α-hydroxyphosphonate (5–14) have been synthesized in high yields by reaction of β-chloro-α,β-unsaturated aldehydes (1–4) and trialkyl phosphite in the presence of chlorotrimethylsilane at room temperature under solvent-free conditions. In addition, compounds (5–14) were reacted with acetic anhydride in DBU to give the new α-acetoxyphosphonate derivatives (15–23). All these phosphonates (5–23) were obtained as mixtures of two (E and Z) isomers and fully characterized by multinuclear (¹H, ¹³C, and ³¹P) NMR, IR spectroscopy and HRMS.     

Organocatalytic synthesis of α-hydroxy and α-aminophosphonates

A new and highly flexible procedure is described for the synthesis of α-amino- and α-hydroxy phosphonates. In the presence of a catalytic amount of oxalic acid (10 mol %), trimethyl phosphite reacts with aldehydes or imines (generated in situ from an aldehyde and an amine) to yield the corresponding coupled products in good yield.     

Oxidative synthesis of benzo[1,4]oxazines from α-branched primary amines and ortho-benzoquinones

The efficient oxidative construction of benzo[1,4]oxazines from simple α-branched amines and ortho-benzoquinones is reported. The procedure pivots on a triethylamine and iodine mediated oxidative ring closure from the ketimine intermediate formed upon their condensation. This reaction was shown to tolerate a variety of α-branched benzylamines and downstream derivatization to substituted benzomorpholine structures was also demonstrated.     

Viscous and dielectric properties of α-tocopherol and α-tocopherol acetate

This article presents the results of the shear viscosity and the dielectric relaxation measurements performed for α-tocopherol and α-tocopherol acetate, two principal compounds from the vitamin E group. The temperature dependence of the viscosity and dielectric relaxation time of the compounds can be very well reproduced with the Vogel–Fulcher–Tammann equation. It was found that for both tocopherols, the viscosity and the relaxation time attain their infinite high value (solid-like state) at the temperature of ～60 K below the transition to the glass state.     

Preparation of n-oxides of α− and α′-A minonicotines

Summary All possible N-oxides of -benzamidonicotine were prepared and were hydrolyzed with hydrochloric acid to N-oxides of the corresponding -aminonicotines.     

Reaction of nitroalkanes with levoglucosenone and its α-bromo and α-iodo derivatives. Cyclopentaannulation of α-halocyclenones

Michael reactions of levoglucosenone and its α-bromo and α-iodo derivatives with α,ω-dinitroalkanes were studied under conditions of chemical and electrochemical generation of base. Procedures were developed for stereospecific fusion of a cyclopentane ring to α-bromo- and α-iodolevoglucosenones, 2-iodocyclopent-2-en-1-one, and 2-iodocyclohex-2-en-1-one by the action of 2,2-dimethyl-1,3-dinitropropane.     

Palladium-catalyzed Hiyama couplings of α-silylenoates and α-silylenamides

The Hiyama couplings of both α-silylenoates and α-silylenamides are described. These sensitive substrate classes require particularly specific conditions, employing both appropriate silicon-based species and a silver additive to realize high yields of the coupling products. Regioselective platinum-catalyzed hydrosilylations provide a direct and convenient entry into these stereodefined trisubstituted alkenes.     

Copolymerization of α-Methylstyrene and Styrene

In this paper, the effects of temperature from 60 °C to 80 °C and the molar ratios in monomer feed on the copolymerization of α-methylstyrene(AMS) and styrene(St) were studied. The resulting copolymers, designated as PAS, were characterized by FTIR, GPC, NMR and TGA. When the reaction temperature was below 75 °C, the molecular weights increased almost linearly as the evolution of the copolymerization. The phenomenon revealed that AMS could mediate the conventional free radical polymerization having some features of a controlled system. As the AMS/St = 50/50(molar) in feed, the overall fraction of the AMS unit incorporated into the copolymer was as high as 42 mol%, the monomer conversion could be more than 90 wt% and the molecular weights could reach as high as 4400. However, since the styrene is more reactive than AMS, the AMS fraction in copolymer increased with the overall monomer conversion. The 13C-NMR revealed the products were random copolymers which had triads, such as-AMS-AMS-AMS-,-St-AMS-AMS-(-AMS-AMS-St-) and-St-AMS-St-. TGA curves demonstrated that the degradation temperature of the resulting copolymers went down from about 356.9 °C(0 mol% AMS) to 250.2 °C(42 mol% AMS). This behavior demonstrated that there exist weak bonds in the AMScontaining sequences which could be used as potential free radical generators.     

Regiospecific Baeyer-Villiger Oxidation of α,α-Dichlorocyclobutanones: A Norbisabolide γ-lactone Analogue1

Details and methodological comparisons are presented on the preparation of a norbisabolide γ-lactone analogue (4) via dichloroketene cycloaddition to limonene followed by regioselective Baeyer-Villiger oxidation (CH₃CO₃H) of the α,α-dichlorocyclobutanones 3 and C-Cl reduction (Zn/HOAc). The sequence of reduction followed by oxidation (HOCI) applied to 3 produced 4 in much better yield.     

A straightforward synthesis of both enantiomers of α-vinylalanine and α-ethynylalanine

This report describes the synthesis of enantiomerically pure (S)- and (R)-α-vinylalanines and (S)- and (R)-α-ethynylalanines, four quaternary α-amino acids, using a straightforward synthetic route and starting from (S)- and (R)-N-Boc-N,O-isopropylidene-α-methylserinals.     

1,4-Addition of tetraethyl fluoromethylenebisphosphonate to α,β-unsaturated compounds

Tetraethyl fluoromethylenebisphosphonate in the presence of cesium carbonate in DMF undergoes efficient 1,4-addition to Michael acceptors having terminal double bond such as α,β-unsaturated ketones, esters, sulfones, sulfoxides, and phosphonates to yield the corresponding adducts (α-alkyl-α-fluoromethylenebisphosphonates) in good to excellent yields.     

Palladium-catalyzed 1,4-addition of diarylphosphines to α,β-unsaturated N-acylpyrroles

Highly stereoselective asymmetric 1,4-addition of diarylphosphines to α,β-unsaturated N-acylpyrroles catalyzed by a PCP pincer-Pd complex has been developed for the synthesis of chiral phosphines with excellent stereoselectivity (91-99% ee) under mild conditions. The products obtained can be further converted into chiral phosphine-oxazoline ligands.     

Palladium-catalyzed 1,4-addition of diarylphosphines to α,β-unsaturated aldehydes

A highly stereoselective asymmetric 1,4-addition of diarylphosphines to α,β-unsaturated aldehydes catalyzed by a bis(phosphine) pincer-Pd complex has been developed for the synthesis of chiral phosphines with excellent stereoselectivity (up to 98% ee) under mild conditions. The application of the current method to the synthesis of enantiopure bisphosphine and its pincer-Pd complex has also been demonstrated.