2,3-Benzotropone (1) has conveniently been prepared from easily available α-tetralone (2) in good overall yield by the following successive reactions: dihalocarbene addition to enol-ether (3) derived from 2, ring-expansion of the adduct (4) to halobenzocycloheptadienone (5), and dehydrohalogenation of 5 giving 1.
Pleiadiene-7,8-dione, o-pleiadienoquinone (I), was synthesized by hydrolysis of acenaphthylene-dichloroketene adduct (III). E1⁄2 value is −0.23 V at pH 5.28. Spectral data suggest that I has the contribution from such canonical forms as 2,3- (Ia) and/or 4,5-benzotropolonate (Ib) structures.
The dichlorocarbene addition to various di- and trimethoxynaphthalenes has been investigated systematically. It has been found that the carbene addition is oriented by the 1-methoxyl group to the 3,4-double bond and by the 2-methoxyl group to the 1,2-double bond of naphthalene nucleus, and that the spontaneous cyclopropane ring-opening of the intermediate carbene-adducts leads to the preferencial formation of 2,3-benzotropone over 4,5-benzotropone derivatives. The steric effects by methoxyl group seem not to be significant in either the carbene-addition or ring-opening reaction.
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Contrary to a report that the reaction of benzo [b]cyclohepta [e][1,4] oxazine 1 with ,-diamine 2b produces 1,2,3,4tetrahydrocyclohepta[b][1,4]diazepine 4, the product was found to be 2-phenyl-3,4,5,6-tetrahydropyrimidine 5b and is peculiar to the reaction of 1 with ,-diamines 2 as well as -aminamide 7.
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