4-Cyclooctene-l-carboxylic acid

Alkylation of 28 with acrolein gives the bicyclic ketone (65), which can be converted to 4-cyclooctene-l-carboxylic acid by the action of base on its methiodide (55a). 

A mixture of 17 g of the methiodide and 32 ml of a 40 % aqueous potassium hydroxide solution is heated with stirring in a flask fitted with a condenser. The heating bath should be kept at 125-130°, and the heating should be continued for 5 hours. The cooled reaction mixture is then diluted with 30 ml of water and washed twice with 25-ml portions of ether. The aqueous layer is cautiously acidified in the cold with concentrated hydrochloric acid to a pH of about 2 and then extracted five times with 25-ml portions of ether. The combined extracts are washed twice with 10% sodium thiosulfate solution and are dried (magnesium sulfate). Removal of the solvent followed by distillation affords about 3 g of 4-cyclooctene-l-carboxylic acid, bp 125-12671-1 mm. The product may solidify and may be recrystallized by dissolution in a minimum amount of pentane followed by cooling in a Dry-Ice bath. After rapid filtration, the collected solid has mp 34-35°. 

Phenylseleno-lactonization of 4-cyclooctene-l-carboxylic acid (41) gives a mixture of six- and seven-membered-ring lactones 42 A and 42B by TLC and H-NMR spectroscopy in a 3 1 ratio. After passing through a silica gel column, however, only one product, the six-membered lactone 42 A, is obtained in 94% yield 3. 

The reaction has also been applied to the conversion of vinyl bromides into acrylic acids, e.g. 1-bromo- and 1-chlorocyclooctene are converted into cyclooctene-1-carboxylic acid (ca. 98%) [3], 2-chloro-3,3-dimethylbut-l-ene yields 4,4-dimethylpent-2-enoic acid (95%), and tams-cinnamic acid is obtained (85%) from fran.v-p-bromostyrene. cis-p-Bromostyrene produces a mixture of cis- and trans-cinnamic acids in 38 and 42% yields, respectively [3]. In these reactions, benzyltri-ethylammonium chloride cannot be used as the phase-transfer catalyst, as it leads to the production of phenylacetic acid [3]. 

Dry diethyl malonate added to a soln. of Na in abs. ethanol, stirred 20 min. at 50° under N2, 5,6-epoxy-l-cyclooctene added, refluxed 3 days, aq. KOH added, and refluxed 1 hr. 10-oxo-9-oxabicyclo[6.3.0]undec-4-ene-ll-carboxylic acid (Y 70%) stirred 0.5 hr. at 80° with diethylamine and formalin soln., Na-acetate and glacial acetic acid added, and heated 15-30 min. at 80-90° 11-methylene-9-oxabicyclo[6.3.0]undec-4-en-10-one (Y 87%). F. e. s. N. Bensel, H. Marschall, and P. Weyerstahl, B. 108, 2697 (1975). 

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