Ketenes, preparation

This Asian species is a major agricultural pest. The pheromone has been proposed to consist of three male-specific compounds, only one of which, (Z)-exo-a-bergamotenal 150, has been reported in the literature [114]. The racemic compound was synthesized starting from farnesoic acid chloride 146 (Scheme 25) [114]. Thus, the vinyl ketene prepared from acid chloride 146 underwent 2+2 cycloaddition to give bicyclic ketone 147. The ketone function was removed by reaction with hydrazine followed by treatment of the resulting hy-... 

Ketene reactivity in intramolecular cycloadditions parallel those in intermolecular reactions in which chloro-, vinyl-, aryl- and alkoxyketenes are more reactive than the alkylketenes. In most instances the ketene is generated by amine dehydrohalogenation of an acid chloride. There are, however, a few examples of ketenes prepared along less conventional routes as by the examples for the formation of 11.150 12,151 and 13.151... 

Thus, [2-1-2] cycloaddition of 2-methylpropene with chloro(2,2,2-trichloroethyl)ketene (prepared in situ from 2,4,4,4-tetrachlorobutanoyl chloride and triethylamine) in cyclohexane yielded 2-chloro-3,3-dimethyl-2-(2,2,2-trichloroethyl)cyclobutanone (70%). This a-chloro-cyclobutanone undergoes a stereoselective cine rearrangement in the presence of triethylamine in refluxing toluene for 20 hours to give cw-(2a,4a)-2-chloro-3,3-dimethyl-4-(2,2,2-tri-chloroethyl)cyclobutanone in 94% yield,which was resolved by means of the diastereomeric salts of their sodium hydrogen sulfite adducts with ( —)- or (- -)-l-phenylethylamine. ... 

When dimethoxyphosphinyl phenyl ketene, prepared by an Rh-catalyzed Wolff rearrangement of dimethyl l-diazo-2-oxo-2-phenylethylphosphonate, is submitted to the action of (trimethylsi-lyl)diazomethane, it gives rise to the corresponding dimethyl 2-(trimethylsilyl)-l-phenylvinylphos-phonate in reasonable yield (44%, Scheme 2.9). ... 

The initial examples of ketene preparation utihzed efimination reactions from carboxylic acid derivatives in the preparation of diphenylketene (1) by the dehalogenation of 2-chlorodiphenylacetyl chloride with zinc (Eqns (4.1)), and the dehydrochlorination of diphenylacetyl chloride... 

Ketene Prepared from Reagent Yield Refer- ence... 

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