Ketene bis

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... 

Ketenes. Derivatives of the compound ketene, CH2=C=0, are named by substitutive nomenclature. For example, C4H9CH=C=0 is butyl ketene. An acyl derivative, such as CH3CH2—CO—CH2CH=C=O, may be named as a polyketone, 1-hexene-1,4-dione. Bis-ketene is used for two to avoid ambiguity with diketene (dimeric ketene). 

In addition to products derived from bis-ketenes, reactions of /7 45) and of diethyl... 

Chelation with copper(ll) Lewis acids has been used to change the reactivity of bis ketenes toward alcohols. The alcoholysis of 52 in the presence of copper acetylaceto-nate derivatives afforded the cyclic lactones 54 (Sch. 14) [35]. The addition of alcohols to 52 without the Lewis acid led to the formation of ketene esters 53 which would not undergo cyclization upon treatment with the copper(ll) complexes. It is suggested that chelation of the bis-ketene in a jr-fashion accounts for the lactone products. Although chiral Lewis acids were used, the products were obtained as racemates probably because of very facile epimerization. 

Cleavage without decarbonylation has been observed with derivatives of cyclobutenedione ("cyclobutadienequinone ), the initial product being either a bis-ketene or a diacyl radical depending on whether the reacting excited state is singlet or triplet. Thus, the product of photolysis 93> of phenylcyclobutenedione in methanol was dimethyl phenylsuccinate plus an unidentified substance. The bis ketene intermediate (14) formed... 

These reactions have been extensively investigated,and photolysis of the bis (chromium(0) Fischer carbene complex) 90 in the presence of the vinylaziridine 91 proceeds through the formation of a nominal bis (ketene metal complex) 92 leading to the bis(azepinone) product 93 (Eqn (4.49))." " Whether formation of the ketene metal complexes are... 

Scheme 10. Chemoselective mono- vs. di-Claisen rearrangement of a glycal bis(ketene acetal) [22]...

The bis-ketene 469, generated in the photolysis of the cyclobutenedione 468, can be trapped with dimethylphenylisocyanide to give the cycloadduct 470 via a [4+1] cycloaddition (yield 82%). ... 

Carbon suboxide can be considered to be the parent bis(ketene). It polymerizes at room temperature in diethyl ether to yield yellow, red, or violet polymers. One recent structural study 31) on these soluble polymers concluded that the original structure proposed by Diels et al. 11) was correct. This structure is shown in Eq. (IV-22). 

The preparation of polymers from bis(ketenes) by the route shown in Eq. (IV-24) has been attempted 16-18, 37). Only ill-defined products resulted 3-5,14,16-18, 32, 37). 

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