Improved Synthesis of 1-Aryl-2, 2-Dichloro-1-Alkanones

Recently¹ we described a convenient synthesis of 1-aryl-2, 2-dichloro-1-alkanones 1 by a reaction sequence involving conversion of the parent alkylarylketones into the corresponding N-cyclohexylketimines, followed by chlorination with N-chlorosuccinimide in carbon tetrachloride to afford N-cyclo-hexyl α,α-dichloroketimines, the latter compounds being hydrolyzed in acidic medium to yield the title compounds 1. The relative inaccessibility of compounds of type 1 in the literature was striking. α,α-Dichloroacetophenones 1 (R=H) are     

Regiospecific synthesis of α-ketoacetals by rearrangement of α-bromo-α-fluoroketones

α-Ketoacetals, derived from alkylaryl-α-diones and with acetalized benzoyl moiety, were synthesized by alkoxide induced rearrangement of α-bromo-α-fluoroalkylarylketones.     

The favorskii rearrangement of dichlorinated methylketones

Twenty-two dichlorinated methylketones have been submitted to Favorskii rearrangement in NaOMeMeOH. Distribution of products is strongly dependent on substitution. Primary dichloromethyl-ketones (R₂ = H) gave rise to Favorskii esters only. Results are explained by a cyclopropanone intermediate, which is formed stereospecifically by disrotative closure of a delocalized zwitter-ion. Opening of the cyclopropanone intermediate is affected by steric and electronic influences. On the contrary secondary dichloromethylketones (R₂ ≠ H) afforded Favorskii esters next to methoxyketones derived from a solvolysis mechanism.     

Acid catalyzed ring closure reactions of electrophilic alkenes

Treatment of -acyl-,β-unsaturated ketones with sulfuric acid or dimethylformamide-hydrogen chloride or p-toluenesulfonic acid gave rise to 3-acyl-2-alkyl-4,5-dihydrofurans. Similar cyclization of -acyl-,β-unsaturated esters initially afforded 3-alkoxycarbonyl-2-alkyl-4,5-dihydrofurans which were transformed into 2-acylbutanolides on further reaction with sulfuric acid.

This acid catalyzed cyclization is strongly dependent upon the substitution pattern of the electrophilic alkenes, the acid used and reaction conditions.     

Studies in organic mass spectrometry—VI. The fragmentation of enol derivatives of acyclic β-diketones

The mass spectra of enol derivatives of β-diketones, such as enol ethers and enaminies are discussed. Their behaviour under electron-impact is in accordance with the fragmentation we suggested for an acyclic β-diketone in the enol form. Rearrangement of the enol functional group is observed in the spectra. This process is a general one, as it show not only migration of oxygen and nitrogen in the enol ethers and enamines, but also migeration of sulphur and chlorine in the thio-ether and in 4-chloro-3-pentene-2-one. Enol derivatives are suitable compounds for determining the branching of alkyl chains in β-diketones.     

Synthesis of α-cyanoenamines : Isolation and characterization of both tautomeric isomers: α-cyanoenamines and imidoylcyanides

α-Cyanoenamines have been prepared in high yield by the reaction of α-chloroaldimines with potassium cyanide in methanol. On gas chromatographic analysis, the α-cyanoenamines were partially isomerized to the tautomeric imidoylcyanides. Both isomers have been isolated and spectroscopically characterized.     

Reactions of N-1(2,2-dichloroalkylidene)amines with potassium cyanide: synthesis of β-chloro-α-cyanoenamines, α-chloroimidates and 2-amino-5-cyan

Reaction of N-1(2,2-dichloroalkylidene)amines, prepared by chlorination of aliphatic aldimines with N-chlorosuccinimide, with excess of potassium cyanide in methanol gave β-chloro-α-cyanoenamines. When the reaction was carried out for a longer period, α-chloroimidates were isolated (except for N-t-Bu compounds). Reaction of the α-chloroaldimines with potassium cyanide in dimethylsulphoxide at 70° gave 1,2-dicyanoenamines while at 120° 2-amino-5-cyanopyrrols were produced via 1,3-dicyanoenamines. The reaction mechanisms are discused.     

Favorskii-type rearrangement of α-chloro ketimines

The first examples of the Favorskii-type rearrangement of α-monochloro ketimines are reported. The regiospecific opening of the intermediate cyclopropylideneamines parallels the opening of cyclopropanones under Favorskii-conditions.