Ketenes, from cyclopropenones

At low temperatures cyclopropenones and enamines or ketene acetals were shown to yield 2-azonia-bicyclo(3,l, 0)hex-3-enolates-3 (371, X=0), which can be isomerized thermally to penta-2,4-diene amides(372, X=0). At elevated temperatures the amides were found to be the principal products arising from C-N-insertion 237) (insertion of the cyclopropenone three-carbon unit into the C-N bond of the enamine). These were accompanied in some cases by 3-aminoenones 373 arising from C-C-insertion 237) (insertion of the cyclopropenone into the C-C double bond of the enamine) and a-amino cyclopentenones 375 formed by Stevens rearrangement of the ylide 369 and cyclopentenones 374 ( condensation 237)). 

Azirines254 in principle react analogously to Schiff bases the 2,3-diphenyl pyridones-4 403 obtained from diphenyl cyclopropenone may well result from a primary betaine 401, which reorganizes to the pyridone-4-system via its valence tautomer, the ketene 402. 

The most general methods for preparing seven- or eight-membered rings from enamines are by ring expansion of the cyclobutene, cyclobutanone or chlorocyclopro-pane adducts formed by cycloaddition of acetylene carboxylates, ketenes or chlor-ocarbenes, respectively, to enamines of cyclopentanone or cyclohexanone. These are two-carbon or one-carbon ring expansions. Three-carbon ring expansions can also be carried out by cycloaddition of activated cyclopropenes or cyclopropenones. 

The reaction of isocyanates and ketenes with diarylcyclopropenones" involves initial electrophilic attack at the carbonyl oxygen of the enone and cyclopropenonimines and triafulvenes are the ultimate products of reaction (Sections II.F and II.G). The formation of the 1 2 adduct 329 from 14 and dehydrobenzene is rationalized by a complex path which, however, involves initial electrophilic attack on the cyclopropenone oxygen atom to give zwitterion 328 (equation 98)" ... 

At low temperatures arylcyclopropenones condense with enamines by 1,2-addition to give the 2-azoniabicyclo[3.1.0]hex-3-en-3-olates 344, which isomerize on heating to penta-2,4-dienamides 348. In an overall sense these products arise from insertion of the cyclopropenone three carbon unit into the C-N bond of the enamine and at elevated temperatures compounds 344 are not isolated. In certain instances, -aminoenones 345, co-aminocyclopentenones 347 and cyclopentenones 346 (next page) also ensue . Ketene acetals behave in a similar manner to enamines . 

Miscellaneous Reactions. A study of the photodissociation of ketene under jet-cooled conditions in the 193-215 nm wavelength range has shown that bond fission to afford H atoms is a principal reaction.Acryloyl chloride undergoes C-Cl bond fission on irradiation at 193 nm. The photodecarbon-ylation of the cyclopropenones (54) occurs quantitatively on irradiation in methanol solution to yield the corresponding alkynes. The quantum yield for decarbonylation for the alkyl substituted derivatives is in the range 0.2-0.3, while for the aryl derivatives = 0.7. A determination of the reaction dynamics for the photodissociation of diphenylcyclopropenone has shown that the dissociation occurs from the So state. 

Ring expansion by 2 C-atoms with cyclopropenones 3-Cyclopentene-l,2-diones from ketenes Ph Ph Ph, , Ph Q... 

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