The Dehydrogenation of ortho-Tropylphenols and the Synthesis of Furano-p-benzoquinonetropides

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Abstract
The intermolecular disproportionation reaction between 2-methoxy-10aH-cyclohepta-[b]benzofuran (4) and 2-acetoxy-3-methoxyphenyltropylium ion (2) occurred upon the treatment of 2 with 2 N hydrochloric acid, thus affording 3′-methoxy-2′, 2-epoxyphenyltropylium ion (5) and 3-(2-acetoxy-3-methoxyphenyl)tropilidene (6). 3H-Cyclohepta[b]benzofuran-3-one (furano-p-benzoquinonetropide) (25), its ethyl (30), chloro (35), acetyl (40) and hydroxy (48) derivatives were synthesized by the application of this disproportionation reaction to the dehydrogenation products of 4-tropyl, 6-ethyl-4-tropyl, 6-chloro-4-tropyl, 6-acetyl-4-tropyl resorcinol and 4-tropylphroglucinol triacetate respectively. The electronic spectra of these furano-p-benzoquinonetropides (25), (30), (35), and (40), in water showed their long wavelength absorption maxima at mμ (logε) values of 540 (3.74), 568 (3.57), 512 (3.83) and 512 (3.51) respectively. However the spectra of these compounds in chloroform showed the peaks at mμ (logε) values of 635 (3.03), 685 (3.61), 665 (3.56) and 600 (3.50) respectively, the peaks had shifted to wave-lengths longer by 100–150 mμ than those in water. This solvent effect, the reverse of the case of p-benzoquinonetropides, may be interpreted in terms of an increased contribution by the polar structure to the ground state as a result of the formation of the furan ring.