Syntheses of the four stereoisomers of Phytophthora mating hormone α2 and a concise synthesis of mating hormone α1

Four stereoisomers of Phytophthora mating hormone α2 were synthesized using both enantiomers of citronellol as starting materials. The absolute configuration of the natural product was determined to be 7S,11R,15R by oospore-inducing assays of the synthetic isomers. A concise synthetic procedure of α1 was also established using a common synthetic intermediate of α2.     

Fluorinated NH-iminophosphonates and iminocarboxylates: novel synthons for the preparation of biorelevant α-aminophosphonates and carboxylates

A convenient synthetic approach to previously unknown N–H α-iminophosphonates and iminotrifluoropropionates was developed. The synthetic potential of N–H iminophosphonates and iminotrifluoropropionates, existing as an equilibrium mixture of E/Z-isomers, was demonstrated by their easy functionalization to afford biorelevant fluorinated α-aminophosphonic and α-aminocarboxylic acid derivatives.     

A General Synthesis of α-Substituted Acrylonitriles

During a study of synthetic approaches to naturally-occurring sesquiterpene lactones, a new synthesis of the α-methylene-y-butyrolactone group was developed¹ and has subsequently been applied to the synthesis of various types of α-methylenecarbonyl compounds.² The synthetic scheme suggested that α-substituted acrylonitriles would also be available by this method.     

The synthetic protocol for α-bromocarbonyl compounds via brominations

α-Bromocarbonyl compound easily generates α-radicals in the presence of a proper initiator, such as copper salt. Recently, tertiary-alkylation reaction using α-bromocarbonyl compound as a tertiary alkyl source is recognized as one of the most important alkylation reactions. The reactions using α-bromocarbonyl compound are increasing, whereas synthetic methods for various functionalized α-bromocarbonyl compounds are not summarized. Generally, α-bromocarbonyl compounds can be synthesized from the corresponding carboxylic acids via α-bromo acid bromide, but the brominations of carboxylic acids are sometimes problematic. In this paper, we will report some technical information for a bromination and synthetic examples of representative α-bromocarbonyl compounds.     

Selective synthesis of α-fluoro-β-keto- and α-fluoro-β-aminophosphonates via electrophilic fluorination by selectfluor

A series of α-mono- and α,α-difluoro-β-ketophosphonates were synthesized in moderate to good yields with excellent selectivities via electrophilic fluorination by Selectfluor. Subsequently, synthetic potential of the obtained α-monofluoro-β-ketophosphonates was demonstrated by their application in synthesis of α-monofluoro-β-aminophosphonates, useful building blocks in the preparation of phosphapeptides.     

A parallel synthesis approach towards a family of C-nucleosides

A synthetic route was devised for a sugar based α-chloroketone, which was subsequently used to generate a family of C-nucleosides via parallel synthetic methodology.     

Fucosyltransferases as synthetic tools: glycan array based substrate selection and core fucosylation of synthetic N-glycans

Two recombinant fucosyltransferases were employed as synthetic tools in the chemoenzymatic synthesis of core fucosylated N-glycan structures. Enzyme substrates were rapidly identified by incubating a microarray of synthetic N-glycans with the transferases and detecting the presence of core fucose with four lectins and one antibody. Selected substrates were then enzymatically fucosylated in solution on a preparative scale and characterized by NMR and MS. With this approach the chemoenzymatic synthesis of a series of α1,3-, α1,6-, and difucosylated structures was accomplished in very short time and with high yields, which otherwise would have required extensive additional synthetic effort and a complete redesign of existing synthetic routes. In addition, valuable information was gathered regarding the specificities of the lectins employed in this study.     

Direct synthesis of α-thio aromatic acids from aromatic amino acids

Modified amino acids are useful synthetic components in both chemistry and biology. Here we describe a simple, scalable two-step procedure to generate α-thio aromatic acids from aromatic amino acids with yields of up to 96%. Diazotization and α-lactone mediated bromination efficiently form the α-bromo acid with retention of configuration. Thiol substitution with mild reagents such as sodium hydrosulfide or sodium trithiocarbonate provides the inverted, free α-thio acid. The mildly acidic soft nucleophile can then be utilized in many synthetic applications.     

Copper catalyzed asymmetric conjugate addition-bromination of α,β-unsaturated ketones: a highly efficient one-pot reaction for the synthesis of chiral α-bromo-β-alkylketones

An efficient one-pot reaction for the synthesis of chiral α-bromo-β-alkyl ketones was developed. The final products were obtained with excellent enantiomeric excess and good isolated yields. The synthetic potential was illustrated by the radical cyclization of the α-brominated ketone.     

Photo-irradiation of α-halo carbonyl compounds: a novel synthesis of α-hydroxy- and α,α′-dihydroxyketones

The reaction of α-halo ketones (α-iodocycloalkanones, α-bromocycloalkanones, α-iodo-β-alkoxy esters, and α-iodoacyclicketones) with irradiation under a high-pressure mercury lamp gave the corresponding α-hydroxyketones in good yields. For α-bromoketones, it was found that α-hydroxylation does not occur. However, α-bromoketones were converted into α-hydroxyketones in the presence of KI. In the case of α,α′-diiodo ketones, α,α′-dihydroxyketones, which up to now have scarcely been reported, were obtained. This reaction affords a new, clean and convenient synthetic method for α-hydroxy- and α,α′-dihydroxyketones.     

α-氨基酸的不对称合成

α氨基酸的不对称合成是合成方法学中的重要组成部分,由此而发展出来的方法成为不对称合成领域中的典范。本文着重从合成方法学角度出发,总结了α－氨基酸不对称合成的最新进展。     

α-羟基取代膦酸酯类化合物的合成研究进展

含磷化合物一直是有机化学研究的热点之一,许多合成药物以及天然产物都含有磷原子。其中,α-羟基取代膦酸酯类化合物是重要的有机合成中间体,其在有机合成中的应用一直受到广泛关注。文章详细综述了α-羟基取代膦酸酯类化合物的合成方法。     

Concise synthetic strategy toward cyclic α,α-disubstituted α-amino acids bearing a δ-nitrogen atom: chiral 1-substituted 4-aminopiperidine-4-carboxylic acids

A concise synthetic strategy toward cyclic α,α-disubstituted α-amino acids, 1-substituted 4-aminopiperidine-4-carboxylic acids have been developed. The synthetic route is a reductive amination of dimethyl bis(dioxolanemethyl)malonate with various amines, followed by Curtius rearrangement. This synthetic route is capable of synthesizing 4-aminopiperidine-4-carboxylic acids bearing a bulky substituent and optically active ones bearing a pendent chiral substituent, by the change of condensed amines.     

Radical-mediated hydroxyalkylation of α,β-unsaturated esters

The radical-mediated hydroxyalkylation of α,β-unsaturated esters with alkyl iodides, trialkylborane, water and KF in THF gave the corresponding α-hydroxy esters. The synthetic advantage of the method was demonstrated by a short-step total synthesis of (±)-tanikolide.     

Enantio- and Site-Selective α-Fluorination of N-Acyl 3,5-Dimethylpyrazoles Catalyzed by Chiral π–CuII Complexes

Catalytic enantioselective α-fluorination reactions of carbonyl compounds are among the most powerful and efficient synthetic methods for constructing optically active α-fluorinated carbonyl compounds. Nevertheless, α-fluorination of α-nonbranched carboxylic acid derivatives is still a big challenge because of relatively high pK_a values of their α-hydrogen atoms and difficulty of subsequent synthetic transformation without epimerization. Herein we show that chiral copper(II) complexes of 3-(2-naphthyl)-l -alanine-derived amides are highly effective catalysts for the enantio- and site-selective α-fluorination of N-(α-arylacetyl) and N-(α-alkylacetyl) 3,5-dimethylpyrazoles. The substrate scope of the transformation is very broad (25 examples including a quaternary α-fluorinated α-amino acid derivative). α-Fluorinated products were converted into the corresponding esters, secondary amides, tertiary amides, ketones, and alcohols with almost no epimerization in high yield.     

Synthesis and application of enantioenriched functionalized α-tetrasubstituted α-amino acids from biocatalytic desymmetrization of prochiral α-aminomalonamides

Catalyzed by Rhodococcus erythropolis AJ270, an amidase-containing microbial whole cell catalyst in neutral phosphate buffer at 30 °C, a number of prochiral α-substituted α-aminomalonamides underwent highly efficient and enantioselective hydrolytic desymmetrization to afford functionalized α-tetrasubstituted α-amino acids in 74-98% chemical yields and 94.0 to >99.5% ee. The presence of a free α-amino (NH(2)) substituent in the substrates was deemed important to ensure high biocatalytic efficiency and enantioselectivity. The synthetic application of biocatalytic desymmetrization was demonstrated by practical chemical transformations of (R)-2-amino-2-carbamoylpent-4-enoic acid to α-substituted serine analogues and a bioactive diamino alcohol derivative.     

A New Synthesis of α-Fluoromalonates from α-Fluoro-α-phosphonyl Malonates Using P-C Bond Cleavage

P-C bond cleavage of α-fluoro-α-phosphonyl malonates using magnesium chloride provides a new synthetic route to α-fluoro malonates.     

Highly enantioselective synthesis of α,α-dialkylmalonates by phase-transfer catalytic desymmetrization

A novel enantioselective synthetic method for the construction of a quaternary carbon center from malonates via phase-transfer catalytic (PTC) alkylation has been developed. The asymmetric α-alkylation of diphenylmethyl tert-butyl α-alkylmalonates with alkylating agents under phase-transfer catalysis conditions (aq 50% KOH, toluene, 0 °C) in the presence of (S,S)-3,4,5-trifluorophenyl-NAS bromide (8) as PTC catalyst afforded the corresponding α,α-dialkylmalonates in high chemical (up to 99%) and optical yields (up to 97% ee) which could be readily converted to versatile chiral intermediates. Notably, the direct double α-alkylations of diphenylmethyl tert-butyl malonate also provided the corresponding α,α-dialkylmalonates without loss of enantioselectivity. The synthetic potential of this method has been demonstrated by the preparation of α,α-dialkylamino acid and oxindole systems.     

Enantioselective direct vinylogous Michael addition of functionalized furanones to nitroalkenes catalyzed by an axially chiral guanidine base

The highly syn-diastereo- and enantioselective direct vinylogous Michael addition of α-thio substituted furanones with conjugate nitroalkenes was demonstrated using an axially chiral guanidine base catalyst. The method provides facile access to enantioenriched α,γ-functionalized butenolides that can be further manipulated, thereby rendering them useful synthetic intermediates.     

Efficient synthesis of α-(fluoro/chloro/methoxy)disulfonylmethane derivatives as tunable substituted methyl synthons via a new C-S bond forming strategy

A new synthetic protocol for the preparation of α-fluoro(disulfonyl)methane and its chloro as well as methoxy analogues has been developed. Due to the synthetic utility of α-fluoro(bisphenylsulfonyl)methane (FBSM) as a versatile synthon in the preparation of various useful fluoromethylated organic molecules, search for an easy and economic for its preparation route has been essential. The C-S bond forming strategy is utilized in this new synthetic approach, which can be applied to a variety of substrates with high efficiency and selectivity.