Solvolysis of 2,3-cyclopenteno-4H-homochromen-4-ol acetate: comparison with the corresponding carbocylic system.

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A novel secondary cyclopropylphenylmethyl acetate was prepared from a chromone skeleton via homochromone derivatives in order to study solvolytic behavior. Reduction of the cyclopropyl ketone (homochromone) with lithium aluminum hydride in ether to the corresponding secondary alcohol, was found to be highly stereospecific giving only one of the geometrical isomers. The alcohol was converted into its acetate and subjected to solvolysis in 80% acetone–water. The acetate was hydrolyzed at the rate of 3×10−5 s−1 (25 °C) undergoing alkyloxygen fission. This rate constant was as high as the most reactive secondary esters in solvolyses ever reported, and about 20 times as high as the corresponding carbocyclic ester by estimation of the same leaving group. Product studies were undertaken in the presence of sodium hydrogencarbonate, and seven-membered hemiacetal was obtained in good yield. The structural characteristics of the homochromenol ester in the solvolysis are discussed and benzohomopyrylium ion, an extremely delocalized homoaromatic species, is proposed as an intermediate carbocation.
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