Bisketene

Ketenes. Derivatives of the compound ketene, CH2=C=0, are named by substitutive nomenclature. For example, C4Hc,CH=C=0 is butyl ketene. An acyl derivative, such as CH3CH2—CO—CH2CH=C=0, may be named as a polyketone, l-hexene-l,4-dione. Bisketene is used for two to avoid ambiguity with diketene (dimeric ketene). 

Cyclopropenone formation should involve the bisketene 46 and its decarbonylation to the monoketene 47 (a valence tautomer of cyclopropenone 44), since photolysis in protic media like ethanol produces diethoxy diethyl tartrate 45) (meso and d,l). This method was also successful in the case of l,2-diphenyl-3,3-dichloro-cyclo-butene dione (48) giving rise to diphenyl cyclopropenone49 (but as for 44 only a moderate yield was produced) ... 

The bromination and hydrolysis of ketenes and bisketenes have been studied. The reaction of the bis(ketene) 289 with bromine has yielded the dibromo fumarate derivative 290, whose /r/mr-con figuration has been confirmed by X-ray crystallography (Scheme 41).366 The hydrolysis of the dibromo fumarate derivative 291 first provided the dibromo derivative (5//)-furanone 292. The prolonged reaction with water afforded the maleic anhydride 293. The methanolysis of the dibromo fumarate derivative 290 has resulted in the formation of an isomeric mixture of dimethyl... 

Bisketenes (11) can decarboxylate and then ring close to give cyclopropenones (12) subsequent further decarboxylation yields alkynes (13). A theoretical study shows that the first reaction is favoured by electronegative substituents, whereas electropositive substituents favour the second. The calculations do not indicate conclusively whether cyclopropenone formation is concerted, or proceeds via a syn-ketenylcarbene (14). 

At the HF/6-31G level, ketenyl carbenes (1) were calculated to be intermediates in the decarbonylation of 1,2-bisketenes (2) to form cyclopropenones." At the MP2/6-31G and B3LYP levels, however, decarbonylation was predicted to form the cyclopropenones directly. The anfi-ketenyl carbenes were found to be 2.2-5.4kcalmoP higher in energy than the syn isomers (1). The mechanism of reaction of [l.l.ljpropellane with singlet dihalocarbene has been reported. ... 

Addition of bromine to bisketene (Mc3SiC=C=0)2 (39) has been shown to produce the fumaryl dibromide (ii)-(40), which rearranged upon warming to furanone... 

In further matrix isolation studies, cyclophanedione (38), was envisioned as a precursor, which upon long wavelength irradiation fragments quantitatively to p-xylylene and bisketene (39) (Scheme 16.14). In contrast to benzannellated derivative 32, however, the latter turned out to be photochemically stable under matrix isolation conditions. 

In a novel method of forming cyclobutanols, titanium(IV) chloride is found to promote the condensation of substituted bisketene silyl acetals 23 with more reactive carbon electrophiles such as acetic anhydride or benzoic anhydride. In each experiment, it is apparent that only one diastercomer of the substituted 2,4-dicarbomethoxycyclobutanols 24 is furnished, as can be vindicated by NMR spectral analysis.33... 

Bisketenes can provide different reaction paths in the reaction with imines (Scheme 18). For example, bisketene (74) does not form p-lactam species like (76). Instead, DFT computations [78] indicate that zwitterionic intermediate (75) leads to the furane intermediate (77) whose cyclization yields aziridine (78). 1,2-, 1,3- and 1,4-bisketenyl benzene react normally to yield mainly bis (p-lactams) [78],... 

Scheme 18 Formation of bicyclic compound (78) in the reaction between bisketene (74) and imine (E)-(62a)...

A short review of the first 100 years of ketene chemistry covers haloketenes, Wolff (g) rearrangements, stereoselective nucleophilic attack, dimerization, cycloadditions, ketene-Claisen and -Cope reactions, bisketenes, and free radical processes.12 ... 

The bisketene, which cannot be isolated, must have the same stereochemistry, because the dimethyl ester B formed from the bisketene by the addition of methanol still is a cw-disubstituted cyclohexane. 

Additional examples of trapping of the bisketene from benzocyclobutenedione (in low yield) by Diels-Alder reactions have also been reported 44). 

One of the reasons for confusion in this area is the fact that cyclobutenediones absorb at much shorter wavelengths than their saturated counterparts, prompting the use of short wavelength light in photolyses this can result in formation of secondary photoproducts. It seems likely that formation of cyclopropenones and of acetylenes is the result of photochemical reaction of bisketenes, the primary products of irradiation. Acetylenes could also be formed from cyclopropenones. 

The photolysis of bis-benzhydrylidenecyclobutanedione 24 to cyclic anhydride 26 in aqueous methanol may involve prior photocyclization to cyclobutenedione 25 followed by photolysis to bisketene and reaction with solvent rather than formation of biradical 27 and subsequent reactions as originally suggested 51 ... 

In the presence of pyridine, photolysis of benzocyclobutene-l,2-dione (196) leads to the formation of pyridine ylide (197), and this is thought to arise by reaction with bisketene formed from the substrate dione rather than from an oxacarbene (198). 3-(2-Hydroxy-4-methoxyphenyl)-4-phenyl-2(5H)-fura-none, one of the photoproducts of 6-methoxybenzofuran-2,3-dione and styrene, has now been synthesised. ... 

Thermal fragmentation of maleic hydrazide in the range of 450°-800°C proceeds by two pathways (a) (2+2+2)-cycloreversion to give acetylene and isocyanic acid as primary products, and (b) a retro-Diels-Alder reaction to give initially diimide and a bisketene. ... 

Carbon suboxide, 0 OC=C=0, an unusually reactive bisketene, functions as an efficient double electrophile, in the synthesis of heterocyclic compounds (1). One would expect that the molecule, having four cumulative ir bonds, should be of considerable interest in the field of polymer chemistry and should have been investigated vigorously. On the contrary, not only has the structure of its polymer not been unequivocally established, but also the physical properties of the polymer and the kinetics and mechanism of the polymerization process have not been studied to any significant extent, even though its polymerization product... 

Paracyclophane readily splits intop-xylylene (147) upon thermolysis due to its strained structure [117]. Therefore it can be used as a starting material to generate reactive intermediates for spectroscopic or kinetic studies [118]. Photolysis of [2.2]paracyclophane-l,10-dione (178) was the way to generate the reactive bisketene l,4-dicarbonyl-2,5-cyclohexadiene (180) in argon at 10 K. The compound was characterized by comparison of the experimental and calculated IR spectrum [119]. 

The diester 87 with the same tetracyclic skeleton as 83 had previously been prepared by Paquette et al. via a domino Diels-Alder reaction of 5,5 -bicyclo-pentadienyl 84 with dimethyl acetylenedicarboxylate (Scheme 20) [73]. The key precursor 84 was obtained by iodine-induced oxidative coupling of the copper cyclopentadienide derived from the sodium derivative. The diester 85 formed along with 86 was transformed into a bissilyl bisenol ether by reductive cleavage of the central bond in the succinate moiety with sodium in the presence of trimethylsilyl chloride. Subsequent hydrolysis of the bisenol ether - actually a bisketene acetal - gave the dienic tetraquinacenedicarboxylate 87. This compound served as the key intermediate in the first synthesis of dodecahedrane 88 [74]. 

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