Carbene chloro

The first synthesis of a cyclopropenone was reported in 1959 by Breslowls who achieved the preparation of diphenyl cyclopropenone (11) by reacting phenyl ketene dimethylacetal with benzal chloride/K-tert.-butoxide. The phenyl chloro carbene primarily generated adds to the electron-rich ketene acetal double bond to form the chlorocyclopropanone ketal 9, which undergoes 0-elimination of HC1 to diphenyl cyclopropenone ketal 10. Final hydrolysis yields 11 as a well-defined compound which is stable up to the melting point (120—121 °C). 

The first cyclopropenone, diphenylcyclopropenone (28), was reported in 1959. This, the most common of the cyclopropenones, was prepared by the reaction of phenylketene dimethylacetal with benzal chloride and potassium r-butoxide. The chlorocyclopro-penone ketal (29) which is produced from these reagents via phenyl (chloro)carbene addition to the ketal undergoes )8-elimination yielding 30 which can be hydrolyzed, in situ, to give the cyclopropenone (equation 25). A series of arylphenylcyclopropenones were prepared using this method. ... 

Due to the high reaction temperature and long reaction times, this method is less suited for the synthesis of thermally labile cyclopropanes. In such cases, the corresponding diazo esters are a better source of alkoxycarbonyl(chloro)carbene and alkoxycarbonyl(bromo)car-bene (see Section 1.2.1.2.4.2.6.2.). However, no alternative exists for transfer of alkoxycarbo-nyl(fluoro)carbenes here, [bromo(ethoxycarbonyl)fluoromethyl]phenylmercury is a more reactive precursor than [chloro(ethoxycarbonyl)fluoromethyl]phenylmercury. Typical examples are shown for the formation of 1, 2, and 3. Further examples are given in Houben-Weyl, Vol.E19b, pl044ff. 

Bis(a-chloroarylidene)hydrazines or 1,2-diaryl-1,2-dichloroethenes [a formal dimer of aryl(chloro)carbene] were sometimes observed as side products when 3-aryl-3-chloro-3/7-di-azirines were decomposed in alkenes. 

E)- or (Z)-isomers can be obtained with R =H by controlling the stereochemistry of the ketene acetal. However, the remainder of the substrate must be inert to attack by chloro-carbenes which will clearly limit the utility of this method. Reformatsky reactions of oxoketene acetals (187) derived from aryl ketones (186) followed by dehydration and hydrolysis or just dehydration... 

Dimethylvinylidine carbene (52) has been shown to add to indole-3-carbaldehyde (53) to mainly yield /3-(dihydroprenyl)indole (54). Aryl- and heteroaryl-chloro-carbenes (55) have been shown to add to 1-azabuta-1,3-dienes via a formal [4- -1]-cycloaddition, involving a transient azomethine ylide (56) giving rise to the corresponding pyrrole (57). A formal [4 -1- l]-cycloaddition is also observed during the addition of a triplet carbene (dicarboethoxycarbene generated with a triplet sensitizer) to cyclooctatetraene which leads to bicyclo[4.2.1]nonatriene (58). ... 

Table 4.4. Cyclopropanation of olefins with phenylthio and phenylthio(chloro)carbene...

Methylthio(chloro)carbene has been generated under phase transfer conditions from dichloromethyl methyl sulfide. This carbene cyclopropanates tetramethyl-ethylene in 43%yield, accompanied by a 24%yield of l,2-dichloro-l,2-Z /5-methyl-thioethylene [24]. 

The rearrangement of metal carbenes can also provide halodienes in a very elegant manner. For instance, Fischer chromium chloro carbenes, generated from CrCl2 and a trihalomethyl group borne by the substrate, were shown to evolve under microwave irradiation to provide stereoselectively (Z, )-l-halo-l,3-dienol esters in... 

---