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.     

Reactivity of α-arylseleno-aldehydes towards halogens and benzeneselenenyl chloride

Chlorination of α-seleno-aldehydes bearing an α-hydrogen gives selenium dichlorides which decompose into α-chloro α-seleno-aldehydes and α-chloroenal. Bromination, in all cases, and chlorination for the other α-seleno-aldehydes lead to the α-halogenoaldehydes.     

Zur Kenntnis der Hydrolyse substituierter Imidazolidinthione-(4)

Imidazolidine-thiones-(4) are hydrolyzed in acid solutions or by ammonium hydroxide. Selective formation of α-aminothioneamides, α-aminocarbonamides, α-aminoesters or α-aminoacids takes place in good yields as a function of the reaction conditions. Hydrolysis of the imidazolidinones-(4) leads predominantly to α-aminoacids. α-Aminothioneamides can be converted into α-aminocarbonamides, α-aminoesters or α-aminoacids under relatively mild conditions.     

Chemoselective mono halogenation of β-keto-sulfones using potassium halide and hydrogen peroxide; synthesis of halomethyl sulfones and dihalomethyl sulfones

The synthesis of α-halo β-keto-sulfones using potassium halide and hydrogen peroxide as a chemoselective mono halogenation reagent and the synthesis of α,α-symmetrical and asymmetrical dihalo β-keto-sulfones and α-halo, α-alkyl and β-keto-sulfones is described. Base induced cleavage of α-halo β-keto-sulfones, α,α-dihalo β-keto-sulfones, and α-halo, α-alkyl β-keto-sulfones afforded the corresponding halomethyl sulfones, dihalomethyl sulfones and haloalkyl sulfones.     

New general synthesis of α-alkoxyketones via α'-alkylation, α-alkylation and α,α'-dialkylation of α-alkoxyketimines

α-Methoxy- and α-ethoxyketones, as important intermediates in organic synthesis and flavor compounds in food chemistry, were synthesized by deprotonation of N-(1-alkoxy-2-propylidene)isopropylamine, prepared by condensation of the corresponding α-alkoxyacetone with isopropylamine, and subsequent reaction of the corresponding 1-azaallylic anions with alkyl halides to afford α'-alkylated, α-alkylated and α,α'-dialkylated ketimines. Hydrolysis of the imino function led to the desired substituted α-alkoxyketones. The ratio of α-, α'-, and α,α'-(di)alkylated compounds depended on the amount of base used and on the nature of the alkylating reagent.     

Inorganic chemistry of vitamin B12; by J.M. Pratt. Academic Press,London and New York, 1972, £6.00 net

Action of dimethyllithium cuprate on α,α-dichloro esters at room temperature leads to the formation of α-chloro α-methyl esters together with non chlorinated α-methyl esters; the same reaction performed at ?70° produces α-chloro ester enolates which upon heating to room temperature are transformed into α-methyl ester enolates. The reaction is applied to β-functional α,α-dichloro esters and one α,α-dichloro ketone.     

Study on the Reaction of α-Ketohemithioacetal

Aromatic α-sulfinyl carboxylic acids can be rearranged to hemithioacetals or other derivatives of glyoxylic acid under the action of acid reagents was first reported by Pummerer¹. Later, Russell and coworkers applied this rearrangement to β-ketosulfoxides, synthesized α-ketohemithioacetal², which can be transformed to α-keto alcohol, α-keto aldehyde and α-hydroxy alcohol, α-hydroxy acid³. Furthermore, Hall and Poet reported that α-ketohemithio-acetal can be rearranged to the corresponding α-hydroxythioester in the presence of magnesium nitrate and sodium acetate or tertiary amine⁴. However, few reports of reaction of α-ketohemithioacetal can be seen in literature.     

Regiospecific synthesis of α-chloro- and α-fluoro-1,2-diones

α-Chloro-1,2-diones and α-fluoro-1,2-diones were prepared from the corresponding α-chloroaldimines by a sequence of reactions involving cyanation to α-cyanoenamines, α-halogenation to form α-chloro- or α-fluoroimidoyl cyanides and addition of organolithium reagents across the nitrile moiety, followed by acidic hydrolysis. All steps are straightforward and occur without side reactions finally leading to regiospecifically chlorinated and fluorinated 1,2-diones in good yields.     

Organocatalyzed asymmetric α-hydroxyamination of α-branched aldehydes: asymmetric synthesis of optically active N-protected α,α-disubstituted amino aldehydes and amino alcohols

Enantioselective direct α-hydroxyamination and α-aminoxylation of α-branched aldehydes using a proline-derived tetrazole catalyst is described herein. α-Hydroxyamination adducts with up to 90% ee were obtained by the reaction of nitrosobenzene with unactivated α-branched aldehydes under mild reaction conditions.     

Nouvelle transposition de carbénoïdes lithiens α-alcoolates: synthèse régiospécifique de α-chlorocétones

Organolithium reagents bearing α-chloro and β-lithium alkoxide functions undergo only α-elimination and transpose to α-chloroenolates, which upon hydrolysis give regiospecific α-chloroketones.     

Copper-Catalyzed CH Oxidation/Cross-Coupling of α-Amino Carbonyl Compounds

Keeping options open: The new and mild title reaction involving indoles selectively furnishes 1 and 2 with the aid of tert-butyl hydroperoxide (TBHP). The method represents the first example of a copper-catalyzed α?arylation of α-amino carbonyl substrates leading to α-aryl α-imino and α-aryl α-oxo carbonyl compounds using a C?H oxidation strategy.     

Synthesis,isolation, and chromatography of perdeuterated α-1,2,3,4,5,6-hexachlorocyclohexane

Perdeuterated α-1,2,3,4,5,6-hexachlorocyclohexane (α-PDHCH) was synthesized and isolated in pure form. α-PDHCH was baseline separated from unlabeled α-HCH by high resolution gas chromatography on different stationary phases. α-PDHCH was also resolved into its enantiomeric forms by application of a chiral GC phase. Furthermore, chiral chromatography of a mixture of labeled α-PDHDH and unlabeled α-HCH resulted in four peaks. Standard solutions of α-PDHCH are recommended both as recovery standard for sample clean-up and as internal standard for the quantitation of chlorinated hydrocarbons with GC/MS or GC/ECD in environmental samples.     

α-乙酰基二硫缩烯酮α碳原子的酰化反应

进行了α-乙酰基二硫缩烯酮与酰氯的酰化反应. 以干燥的二氯甲烷为溶剂, 在四氯化钛催化下, α-乙酰基环二硫缩烯酮(1)可与脂肪及芳酰氯(2)反应, 在化合物1的α-碳原子上发生酰化反应, 以较高的产率生成各种α-乙酰基-α-酰基二硫缩烯酮(3).     

α-methyl amino acids by catalytic phase-transfer alkylations

The α-methyl amino acids, α-methyl p-chlorophenylalanine, α-methyl p-tyrosine, α-methyl m-tyrosine and α-methyl DOPA have been prepared in good yields from amino ester hydrochlorides. The key step in the method is the catalytic phase-transfer alkylation of Schiff base derivatives of mono alkyl amino acids.     

Reduction and Reductive Alkylation of α-tert-Butylthio Carbonyl Compounds. An Efficient Method for Stepwise α-Alkylation of Esters,Nitriles and Ketones Via the α-Tert-Butylthio Derivatives

An efficient and generally applicable method for stepwise α-alkylatton of esters, nitriles, and ketones via the α-tert-butylthio derivatives is described. The method involves reductive-protonation and reductive-alkylation of α-alkylthio α,α-bis-alkylated carbonyl compounds which are prepared by stepwise alkylation of the corresponding simple α-alkylthio carbonyl precursors. The reduction is conveniently performed by use of stoichiometric amounts of a dissolving metal, particularly lithium, affording correspondingly the α-mono-and the α,α-bis-alkylated carbonyl compounds in good yields.     

Synthesis and Diels-Alder reactions of α-fluoro- and α-trifluoromethylacrylonitriles

A novel synthetic method for the preparation of α-fluoro- and the still unknown α-trifluoromethylacrylonitriles is elaborated. The reaction of α-fluorovinylbromides and α-trifluoromethylvinylbromides with CuCN leads to the title compounds in good to high yields. While the α-fluoroacrylonitriles were isolated as mixture of Z/E-isomers, the α-trifluoromethylacrylonitriles were obtained as pure Z-isomers. The α-trifluoromethylacrylonitriles are shown to be excellent dienophiles for Diels-Alder reactions.     

Stereocontrolled synthesis of α-amino-α'-alkoxy ketones by a copper-catalyzed cross-coupling of peptidic thiol esters and α-alkoxyalkylstannanes

A stereocontrolled synthesis of α-amino-α'-alkoxy ketones is described. This pH-neutral copper(I) thiophene-2-carboxylate (CuTC)-catalyzed cross-coupling of amino acid thiol esters and chiral nonracemic α-alkoxyalkylstannanes gives α-amino-α'-alkoxy ketones in good to excellent yields with complete retention of configuration at the α-amino- and α-alkoxy-substituted stereocenters.     

The conformation of α-substituted cyclohexanones. Group VI-A substituents

α-Phenylthio-, a α-phenylsulfono- and α-phenylseleno-cyclohexananone have the prefered conformation with the substituent axial whereas the α-phenoxy and α-phenylsulfoxo-cyclohexanones have the substituent equatorial.     

Reactivity of α-chloro-aldimines

A series of secondary N-1-(2-chloroalkylidene)amines has been prepared by condensation of disubstituted acetaldehydes with primary amines followed by chlorination with N-chlorosuccinimide in carbontetrachloride. A study of the reactivity of these N-homologues of α-chloroaldehydes is described. Treatment of the title compounds with sodium methoxide in methanol gave high yields of α,β-unsaturated aldimines. However, N-1-(2-chloro-2-methylpropylidene)amines afforded a mixture of elimination and rearrangement products, which proceeded via an aziridine intermediate. On the other hand, α-phenyl-substituted α-chloro aldimines on treatment with methoxide in methanol underwent α-substitution, consistent with an S_N1 mechanism. Powerful nucleophiles such as sodium thiophenolate in methanol and sodium azide in acetone caused α-substitution. Reaction of α-chloro aldimines with Grignard reagents produced coupling of two aldimine units or α-alkylation. Finally the reactivity of α-chloro aldimines was compared with the reactivity of the corresponding oxygen-analogues, i.e. α-chloro aldehydes.     

Reactions with α-substituted cinnamonitriles. A novel synthesis of hexa-substituted pyridines

Whereas acetoacetanilide (II) reacted with α-cyano- and α-benzoylcinnamonitrile derivatives Ia-e to give hexa-substituted pyridines III and V, it reacted with α-carboxamido- and α-thiocarboxamidocinnammonitrile derivatives If-h to afford penta-substituted pyridines VI. One mole of acetonedicarboxylic acid dianilide (VII) reacted with two moles of each of α-cyano- and α-thiocarboxamidocinnamonitriles Ia,b,f,g to yield the dipyridyl ketones VIII and IX, respectively. On the other hand, α-benzoyl- and α-ethoxycarbonylcinnamonitriles Ic,d,i,j reacted with VII in equimolecular ratio to give the pyran derivaties X and XI, respectively. Several schemes were proposed to illustrate reactions steps. The structures of the synthesized compounds were proved by chemical and spectral methods.