2.2- Dichlorovinyl ketones

Variations in the reaction temperature and in the proportions of the ketone and PCI5 were appreciably reflected in the ratio of the amounts of compound 9 obtained in the first stage to the total content of 7 and 8 and then proportionally in the composition of the final products. In the interaction of the ketones with PCI5, an excess of the latter and high temperature make the anomalous reactions more significant. 4-(l,2-Dichlorovinyl)-3,5-dimethyl-l//-pyrazole (9) was obtained individually by the action of more than a twofold excess of PCI5 on the acetylpyrazole 6 at 80°C in 50% yield. Under the influence of NaNHa in liquid NH3, dichloroethy-lene 9 was converted into chloroacetylene 10 by loss of a molecule of HCl (yield 77%) (Scheme 28). 

Dichlorovinylation. This reaction can be used to prepare a- and y-acetylenic ketones (equation 1).1... 

Dichlorovinylation. Enolate dichlorovinylation with trichloroethylene involves proton elimination to form dichloroacetylene as the actual electrophile.1 Dichloroac-etylene can be prepared by reaction of trichloroethylene with Li N[Si(CH3)j]2 followed by distillation. In the absence of a proton donor, it reacts with a variety of tertiary enolates to give a-chloroethynyl ketones and esters in 43-90% yields. 

Dlchlorovinylation. Enolates of ketones react with 1 to form a-dichlorovinyl ketones, which can be converted into o-acetylenic ketones (equations I and II). 

The formation of desaurins from ketones, carbon disulfide, and base 1275,1281,1282,1285-1290 believed to involve nucleophilic attack on a thioketene by the dianion of a 1,1-dimercaptoalkene, as shown for the synthesis of 572. Related syntheses involve the use of thiophosgene instead of carbon disulfide and the use of diazoalkanes or phosphonium and sulfonium ylides instead of a ketone and base. Treatment of perfluoroiso-butylene with fluoride ion and elemental sulfur in a dipolar, aprotic solvent ° °° or with sources of anionic sulfur (potassium sulfide, sodium hydrosulfide,potassium thiocyanate,sodium thiosulfate, dithiocarbamate salts, dithiophosphate salts ) give the dimer (573) of bis(trifIuoromethyl)-thioketene. Similarly, other 2,4-bis(methylene)-l,4-dithietanes are obtained by treating 2,2-dichlorovinyl ketones with anionic sulfur re-... 

By action of excess secondary amine on chloroform in the presence of sodium alkoxide some form-amidinium salts (182 equation 102) have been prepared. The aminolysis of. -dichlorovinyl ketones or trihalocyclopropenes gives rise to the amidinium salts (183) and (184) (Scheme 24), respectively. ... 

Thus, dichlorocarbene, generated in a neutral medium by using bromodichloro-methyl(phenyl)mercury, underwent addition to 4-methylpent-3-en-2-one (the product is unstable), and to various 2,2-dichlorovinyl ketones. 

Recently, the dehalogenation method was further modified by using 1,2-dichlorovinyl ethers 62 as starting compounds" ". Loffler and Himbert applied the reaction of 1,2-dichlorovinyl ethers 62 with butyllithium to generate lithium alkoxyacetylides 61, which were subsequently quenched with ketones or arylated by the palladium-catalyzed crosscoupling with aryl halides to yield alkoxyarylacetylenes 63 (equation 37)". ... 

Trichloroethylene serves as an effective reagent fc)- the dichlorovinylation of lithium enolates of several conjugated ketones. Under similar reaction conditions, 2,6-d1methylcyclo-2-hexen-l-one and 2-ethyl-5-methoxy-l-tetra1one give the analogous dichlorovinyl adduct in comparable... 

Sodium hydroxide (s. a. under HCl) 2-Ghlorochromones from 2,2-dichlorovinyl ketones... 

Typical features in Reaction scheme 93 are the transformation of a dichlorovinyl-group of 144 into a chloroacetyl-group 145 by intermediate involvement of phenolate and the following Ruthenium-catalyzed addition of carbon tetrachloride, which involves a migration of the ketone moiety to give the mixture 146,... 

Reaction of allyl-l,l-dichlorovinyl ethers with n-BuLi followed by reaction with ketones, epoxides, and oxetanes has been reported to provide 0-, y-, and 6-lactones... 

Trichloroethylene reacts with enolates, via intermediate formation of dichloro-acetylene, to give a-dichlorovinyl ketones, and chloroacetylenes substituted with sulphur, halogeno, and aryl groups react as Michael acceptors with simple enolates to yield the corresponding a-vinyl ketones. ... 

A condensation of vinyl sulphides of synthetic value involves the reaction of a-ethylthio-styrenes with an aldehyde in the presence of a Lewis acid catalyst to give 3-ethylthio-indenes. Regiospecific and stereospecific pentannelation i.e, fusion of a cyclopentane ring) of an alicyclic ketone involves arylthiomethylen-ation followed by base-catalysed addition to an aj8-unsaturated ester. a-Phenyl-thiobutenolides are less reactive Michael acceptors than their sulphoxide counterparts, and /SjS-dichlorovinyl sulphides are less reactive in electrophilic reactions than their oxygen counterparts. Dimerization of aryl a-cyanovinyl sulphides occurs more readily than that of alkyl analogues, since the intermediate 1,4-diradical ArSC(CN)CH2CH2d(CN)SAr, which cyclizes to the cyclobutane, is more stable. Products obtained by photolysis of methyl vinyl sulphide are accounted for by homolysis of both vinyl—S and methyl—S bonds. The kinetics of catalysed cis-trans isomerization of aryl vinyl sulphides have been studied. ... 

A new route to 1,3-thiazinethiones with a wide variety of substituents is provided by the reaction of j8j8-dichlorovinyl aryl ketones with primary thioamides in a molar ratio of 1 2. Thus (9) reacts with thiobenzamide in boiling acetic acid to give (10), which, by sequential treatments with mercuric acetate and oxalyl chloride, can be converted into the thiazinium salt (11)... 

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