William T. Brady

Halogenated ketenes—IV : Cycloadditions of alkylhaloketenes☆☆☆

Abstract Methylbromo, ethylbromo- and ethylchloroketenes have been prepared and undergo 1,2-cycloaddition with cyclopentadiene to form bicyclo[3.2.0]hept-2-en-6-ones. The cycloadducts were prepared by generating the alkylhalokenes by dehydrohalogenation of the appropriately substituted acid halide in the presence of cyclopentadiene. Methylchloroketene also undergoes cycloaddition very readily with ethyl vinyl ether. cis and trans Isomers were produced in all cases and the isomer distributions determined.

Phenyl(trimethylsilyl)ketene. Some ketene reactions with diazomethane

Abstract Phenyl(trimethylsilyl)ketene was prepared by the zinc dehalogenation of phenyl(trimethylsilyl)bromoacetyl chloride. This ketene parallels tirmethylsilylketene in stabibility and lack of reactivity in cycloaddition reactions. The reaction of phenyl(ethyl)-, phenyl(trimethylsilyl)- and trimethylsilylketenes with diazomethane at −78°C is described. Only the 2 1 cycloadducts, the cyclobutanones, could be isolated.

Rearrangements of 8-chloro-8-methylbicyclo[4.2.0]oct-2-en-7-one

The endo- and exo-methyl isomers of 8-chloro-8-methylbicyclo[4.2.0]oct-2-en-7-one were separately treated with aqueous sodium carbonate, aqueous sodium hydroxide, silver nitrate in methanol, and sodium methoxide in methanol. A stereospecific ring contraction and an allylic substitution involving the enol form of the bicyclic ketone were found to be dependent on the base. Thermal rearrangement of the title compound resulted in the formation of propiophenone.

Halogenated ketens. Formation of allenes by the pyrolysis of halogenated oxetan-2-ones

Cycloadducts derived from the cycloaddition of alkylchloroketens and chloral were decarboxylated over a hot wire to produce trichloromethylallenes.

The reaction of dimethylketen with some acid halides

The addition of several acid halides to dimethylketen to produce β-keto-acid halides is described. A correlation exists between the reactivity of the acid halide and the pKa of the acid from which the acid from which the acid halide is derived. Dimethylketen is more reactive than diphenyl- and phenylethyl-keten. This is not a general reaction of keten and acid halides.