Diverse synthesis of the C ring fragment of bryostatins via Zn/Cu-promoted conjugate addition of α-hydroxy iodide with enone

A convergent approach to 1,5-hydroxy ketones,the general precursors for constructing the C ring of bryostatins,has been developed via a Zn/Cu-promoted conjugate addition of a-hydroxy iodides with enones.The reaction leads to direct formation of the C21-C22 bond and tolerates diverse functionalities at the C17-,C18-and C24-positions.The approach also enables a more concise synthesis of the known C ring intermediate(10 longest linear steps and 14 total steps),in contrast to its previous synthesis(17 longest linear steps and 22 total steps) in our total synthesis of bryostatin 8.     

A practical synthesis of α-bromo/iodo/chloroketones from olefins under visible-light irradiation conditions

A practical synthesis of α-bromo/iodo/chloroketones from olefins under visible-light irradiation conditions has been developed.In the presence of PhI(OAc)₂ as promoter and under ambient conditions,the reactions of styrenes and triiodomethane undergo the transformation smoothly to deliver the corresponding a-iodoketones without additional photocatalyst in good yields under sunlight irradiation.Mea nwhile,the reactions of styrenes with tribromomethane and trichloromethane generate the desiredα-bromoketones and a-chloroketones in high yields by using Ru(bpy)₃Cl₂ as a photocatalyst under blue LED(450-455 nm) irradiation.     

Gallium trichloride-catalyzed conjugate addition of indole and pyrrole to α,β-unsaturated ketones in aqueous media

Michael addition of indole and pyrrole to a variety ofα,β-unsaturated ketones was efficiently promoted by a catalytic amount of GaCl_3 in aqueous media to afford the corresponding products in good to excellent yields.     

Convenient synthesis of α-bromo ketones by the Meerwein reaction

A simple and convenient procedure was proposed for the synthesis of 4-aryl-3-bromobutan-2-ones from methyl vinyl ketone and arenediazonium bromides under Meerwein reaction conditions.     

NBS-assisted an efficient conversion of styrenes to α-hydroxy ketones in water

An expedient, mild and environmentally benign method for the oxidation of styrenes to α-hydroxy ketones has been developed. This conversion has been achieved by employing water as a solvent as well as an oxygen source. This facile and efficient tandem process provides α-hydroxy ketones in moderate to good yields from easily accessible styrenes.     

Copper-catalyzed synthesis of α-ketothioamides from ketones

In this paper, the conversion of acetophenone to α-ketothioamide was reported in the presence of CuI as the catalyst and S₈/DMF as the coupling partners. The presence of both KF and NaOH was found to be necessary to achieve the high yield of the product. Propiophenone and butyrophenone also reacted in the presence of phenylboronic acid as an additive. Willgerodt-Kindler products were not observed in these reactions.     

Stereoselective cycloaddition of N-acyliminium cations withα,β-unsaturated ketones and esters

The cycloaddition of N-acyliminium cations with some deactivated alkenes such asα,β-unsaturate ketones and esters has been investigated.In most cases,the N-acyliminium cations produced from 3-hydroxy-2-arylisoindol-1-ones in the presence of BF_3·OEt_2 could be reacted withα,β-unsaturated ketones and esters to afford stereoselectively the cycloaddition products 6-acylisoindolo[2,1-a] quinolin-11-ones in moderate to high yields.     

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.     

Synthesis of α,β-Unsaturated Ketones using Potassium fluoridealumina Catalyst by Microwave Irradiation

Microwaveirradiationhasf0undalotofapplicati0nsinrecentyears'".Thereactiontimecanbeshortenedgreatlyundermicrowaveirradiation,soitisanewandconvenientsyntheticmethod.Inprevi0uspapers"',wereportedtheethoxylationsofnitro-chlorobenzeneandreactionsofcarboxylicacidwithhalidesunderndcrowaveirradiation.a,6-Unsaturatedketonesareusefulcompounds,whosesynthesiswerenoteasybyconventionalways"9.Ontheotherhand,KF-Al2O3isanewkindofbasecatalyststhatcancatalyzemanyreactionsunderndldconditions,t0givehighcatalytic…     

Regiospecific synthesis of α-arylsulfonoxy ketones from ketone derivatives

Isomeric enol ester, enamine, and silyl enol ether derivatives of unsymmetrical ketones are converted regiospecifically to α-arylsulfonoxy ketones with arylsulfonyl peroxides.     

One-pot asymmetric synthesis of α-trifluoromethylated amines from α-trifluoromethyl ketones

Diastereoselective reduction of (Rs)-N-tert-butanesulfinyl α-trifluoromethyl ketimines formed in situ from the corresponding α-trifluoromethyl ketones and N-tert-butanesulfinamide has been achieved, and either diastereomer of N-tert-butanesulfinyl α-trifluoromethyl amines was obtained in good yields with excellent diastereoselectivities (up to 99:1 dr) using NaBH₄ and L-Selectride as the reductants, respectively.     

Concise synthesis of α-trisubstituted amines from ketones using N-methoxyamines

Three-component allylation and cyanation utilizing a ketone and an N-methoxyamine are reported. The high nucleophilicity of the N-methoxyamine and high electrophilicity of the corresponding iminium ion enable the concise synthesis of α-trisubstituted amines in a single step.     

Enantioselective synthesis of β-hydroxy ketones from heterocyclic aldehydes in water catalyzed by a recyclable organocatalyst bearing an ionic liquid moiety

The aldol reactions of cyclic (heterocyclic) ketones and heterocyclic aldehydes catalyzed by (4R,S)-4-hydroxyproline modified with a ionic liquid moiety proceed with high yields and diastereo- and enantioselectivity in the presence of water. The catalyst retained its activity and selectivity for at least five cycles.     

Spectrometric study ofα-methylene aromatic araminenone and aminoketone

Thirteenα-methylene aromatic araminenone and fourα-methylene aromatic aminoketones were prepared by modified Mannich reaction.On the basis of isotopic labeling,a plausible way of cleavage was proposed for the formation of the M~ -17 fragment peak in the MS of theα-methylene aromatic araminenone and aminoketones.The characteristic chemical shift of the olefinic protons in ~1H NMR is also discussed.     

Facile synthesis of α-hydroxy carboxylic acids from the corresponding α-amino acids

An effective and improved procedure is developed for the synthesis of α-hydroxy carboxylic acids by treatment of the corresponding protonated α-amino acid with tert-butyl nitrite in 1,4-dioxane–water. The amino moiety must be protonated and located α to a carboxylic acid function in order to undergo initial diazotization and successive hydroxylation, since neither β-amino acids nor acid derivatives such as esters and amides undergo hydroxylations. The method is successfully applied for the synthesis of 18 proteinogenic amino acids.     

Silafunctional compounds in organic synthesis. 29.1 Oxidation of (alkenyl)alkoxysilanes to α-hydroxy ketones

(Alkenyl)alkoxysilanes are readily transformed into α-hydroxy ketones via epoxidation and the subsequent oxidative cleavage of the carbon—silicon bonds.     

Asymmetric reduction of α-hydroxy aromatic ketones to chiral aryl vicinal diols using carrot enzymes system

Asymmetric reduction ofα-hydroxy aromatic ketones was carried out by using carrot enzymes system,yielding corresponding chiral vicinal diols with special functional groups.The optimum reaction conditions were obtained after investigation of various influencing factors.Chiral aryl vicinal diols were produced with good yields and excellent enantiomeric excesses under appropriate conditions.Meanwhile,the steric factors and electronic effects of the substituents on the aromatic ring were shown to have an interesting influence on both yield and enantioselectivity.     

The NHCs-mediated cross-coupling of aromatic aldehydes with benzyl halides: synthesis of α-aryl ketones

A new NHCs-mediated synthetic method was found to produce α-aryl ketones in 22-63% yields in one-pot process from the corresponding aromatic aldehydes and benzyl halides. This method is the first example of the NHCs-mediated intermolecular nucleophilic acylation of aromatic aldehydes with benzyl halides.     

Total synthesis of human urotension-Ⅱ by microwave-assisted solid phase method

Human urotension-Ⅱwas synthesized efficiently on Wang resin under microwave irradiation using Fmoc/tBu orthogonal protection strategy.Disulphide bridge was formed on solid phase with the irradiation of microwave,then the whole peptide was cleaved from the resin.The purity of crude peptide cyclized under microwave irradiation was higher than that under room temperature.