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Part I. A Novel Synthesis of Dihydrojasmone. — 3-Methylcyclopent-2-en-2-ol-l-one, a readily available substance of natural occurrence, was utilized in the synthesis of the well-known dihydrojasmone (2-n-aniyl-3-methylcyclopent-2-en-l-one). This was the first practical synthesis of dihydroJasmone which did not involve a condensation reaction, thus the possibility of obtaining an isomeric mixture of products was eliminated.

Acetylation of 3-methylcyclopent-2-en-2-ol-l-one with acetic anhydride gave 2-acetoxy-3-methylcyclopent-2-en-l-one, which was converted by the action of propylene oxide to 2-acetoxy-3-methylcyclopent-2-en-l-one propylene ketal. Saponification of this ketal gave 3- methyl-l,2-cyclopentanedione-l,l-propylene ketal, which served as a precursor to dihydrojasmone. Upon treatment of this compound with n-amylmagnesium chloride, followed by hydrolysis with ammonium chloride solution, 2-n-amyl-3-methylcyclopentan-2-ol-l-one propylene ketal was obtained. Dehydration and deketalization of the latter compound with sulfuric acid solution yielded dihydrojasmone.

Part II. Polymethyleneketene Dimers and Trimers. — An excellent method for the preparation of ketoketene dimers involves the dehydrohalogenation of an acyl chloride with triethylamine. The reaction of cyclopropanecarbonyl chloride with triethylamine gave no dimer but instead a solid product, presumably the acyl ammonium chloride, which reacted with aniline to form cyclopropanecarboxanilide. Cyclobutanecarbonyl chloride and triethylamine yielded at temperatures below 25® a similar addition compound which gave cyclobutanecarboxanilide when treated with aniline. When the latter reaction was carried out at a higher temperature, dispiro [] decane-5,10-dione was obtained. Dispiro [] decane-5,10-dione, trimethyleneketene dimer, underwent cleavage and decarboxylation in alkali to give dicyclobutyl ketone. The ketone was obtained without acidification of the alkaline solution, which is generally necessary for the decarboxylation of a β-keto acid in the form of its sodium salt. A mechanism was proposed for its formation. Trimethyleneketene dimer reacted with ethanol in the presence of a catalytic amount of base to give ethyl l- (cyclobutanecarbonyl)cyclobutanecarboxylate, and was reduced to the corresponding glycol, dispiro [] decane-5,10-diol with lithium aluminum hydride.

It is known that dimethylketene dimer, tetramethyl-l,3-cyclobutanedione, when treated with a catalytic amount of sodium methoxide, yields the cyclic trimer, hexamethyl-l,3,5-cyclohexanetrione. In the present investigation, this base-catalyzed process was utilized in the synthesis of trimethyleneketene trimer, trispiro [] pentadecane-5,10,15-trione, from trimethyleneketene dimer.

In this study it was found that the alkaline hydrolysis of dimethylketene trimer with barium hydroxide gave 2,4,4,6-tetramethylheptan-3,5-dione. Trimethyleneketene trimer, upon treatment with the same reagent gave l, l (dicyclobutanecarb6nyl) cyclobutane and dicyclobutyl ketone. Ethanolysis of trimethyleneketene trimer gave ethyl 1-[1-(cyclobutanecarbonyl)cyclobutanecarbonyl] cyclobutanecarboxylate. Reduction of the trimer was accomplished with lithium aluminum hydride to give trispiro [] pentadecane-5,10,15- triol.

Tetramethyleneketene dimer, dispiro [] dodecane-6,12-dione, a known compound, was the only product isolated in an attempted synthesis of tetramethyleneketene monomer by dehydrohalogenation of cyclopentanecarbonyl chloride with triethylamine. The dimer underwent cleavage and decarboxylation when treated with alkali to give dicyclopentyl ketone.

Only one polymethylene ketene, pentamethyleneketene, has been reported in the literature. It was found that hexamethyleneketene could be synthesized by dehydrohalogenation of cycloheptanecarbonyl chloride with triethylamine. This monomer reacted with aniline to give cycloheptanecarboxanilide, and gave with cyclopentadiene a cycloaddition product, hexamethylenebicyclo [3.2.0] hept-3-en-l-one. Hexamethyleneketene dimerized upon standing to give dispiro- [] hexadecane-8, l6-dione which underwent reduction with lithium aluminum hydride to give the corresponding glycol, dispiro [] hexadecane-8,l6- triol.