Photochemical reactions of 2-bromotropone and 2,7-dibromotropone with 9,10-dicyanoanthracene

Abstract

The photochemical reactions of 2-bromotropone and 2,7-dibromotropone with 9,10-dicyanoanthracene gave products with anthracene, anthracenone, and dihydroanthracene skeletons both in polar and non-polar solvents. These products were formed by attack of water contaminated in the solvent, by attack of the troponoid, and by attack of the solvent used in the reactions, respectively, on a reaction intermediate. In a mixed solvent of benzene and methanol, a benzaldehyde derivative with a tribenzo-2-oxabicyclo[3.2.2]nonane system was obtained. This result was informative about the reaction mechanism, and suggested the formation of an [8 + 4]pi cycloadduct with a tribenzo-2-oxabicyclo[3.2.2]nonane system between the troponoid as the 8 pi component and the 9,10-dicyanoanthracene as the 4 pi component. In non-polar benzene, a new tetrabromodihydroanthracene derivative was obtained together with anthracenone and anthracene derivatives. It was proved by the reaction in benzene-d6 that the new product was formed by attack of benzene-d6.

meta-Photoaddition reactions of 2-chloro-, 2,5-dichloro-, and 2-halo-5-isopropyl-tropones with 9,10-dicyanoanthracene

“…Similarly, irradiation of a dichloromethane solution of 2,5-dichlorotropone (9) and DCA gave product 10 in 36% yield. The 1 H NMR spectrum indicated that two structures 10a and 10b are possible since the four tropone ring protons appeared as two sets of the AB quartet.…”

“…An isomer of 13 has been obtained as one of the photoproducts in the reaction of 2,7-dibromotropone and DCA. 9 The chemical shifts Similarly, 2-bromo-5-isopropyltropone (14) gave a bromo derivative 15 of 12 in 85 and 84% yields in benzene and in dichloromethane, respectively and in 69% yield in a mixed solvent of acetonitrile and dichloromethane (Scheme 5).…”

“…15 The similar mechanism has been proposed in the reaction of 2,7-dibromotropone and the excited DCA. 9 Next, a methoxide ion attacks the cycloheptatrienyl ion (19b) to give a 7-isopropyl-7-methoxycycloheptatriene derivative (20). Since the oxidation potential of cycloheptatriene 20 should be lower than 2-halotropones, 9,16 an electron-transfer reaction would occur from 20 to DCA to give a cation radical (21).…”

“…The spectral data are similar to a bromo derivative of 5, which has been obtained in the reaction of 2,7-dibromotropone and DCA. 9 Therefore, the structure of 5 was assigned to be an anthracenone derivative. The structure of 6 was determined to be a 1,1a,8,8a-tetrahydro-9-oxo-2,7(1 0 ,2 0 )-benzeno-1,8-propenobenzo[a]cyclopropa[d]cycloheptene-2,7-dicarbonitrile derivative, a metaadduct by the 1 H and 13 C NMR spectroscopic data by comparison of the meta-adduct (2) obtained from the reaction of 1 and DCA.…”

“…9 From the results of solvent effects, we proposed an ionic mechanism in polar solvents and a radical mechanism in non-polar solvents in the reaction of halotropones with DCA. In this paper, we report the photoreaction of the excited DCA with 2-chloro-, 2,5-dichloro-, and 2-halogeno-5-isopropyltropones to propose the mechanism of the meta-adduct via a bicyclo[4.…”