K. Dawes

Light-induced and related reactions of quinones. Part VIII. Some (2-hydroxyalkyl)-, phenethyl-, (2-ethoxycarbonylethyl)-, and styryl-1,4-benzoquinones

The synthesis of 1,4-benzoquinones carrying, severally, the side-chains [CH2]2·OH, CH2·CH(OH)Me, [CH2]2·Ph, CH2·CHPh2, [CH2]2·CO2Et, CH2·CH(CO2Et)2, cis- and trans-CHCHPh, CHCPh2, and CO·CHCHPh is described. When irradiated with visible light the hydroxyalkylquinones yield the corresponding carbonyl compounds. The phenyl-, diphenyl-, and ethoxycarbonyl-ethylquinones and the β-phenylstyrylquinone give 2,3-dihydrobenzofurans. Mechanisms are discussed. Diethyl (1,4-benzoquinonyl)methylmalonate is essentially unchanged. The remaining quinones afford unidentified amorphous products.

Light-induced and related reactions of quinones. Part X. Further studies with hydroxymethyl-, vinyl-, and (2-ethoxycarbonylethyl)-1,4-benzoquinones

Irradiation of hydroxymethyl-1,4-benzoquinone in [2H6]benzene gave ([2H5]phenoxymethyl)-1,4-benzoquinone, with no incorporation of deuterium into the quinonoid nucleus. Irradiation of 2-hydroxymethyl-5- and 2-hydroxymethyl-6-methyl-1,4-benzoquinones in benzene gave the corresponding methyl homologues of phenoxymethyl-1,4-benzoquinone, but 3-methyl-2-phenoxymethyl-1,4-benzoquinone was not formed from 2-hydroxymethyl-3-methyl-1,4-benzoquinone.Irradiation of [3,3,3-2H3]-2-(1,4-benzoquinonyl)propene in benzene gave 3-[2H3]methyl-5-hydroxybenzofuran with neither loss nor scrambling of the label. 1-(1,4-Benzoquinonyl)-1-phenylethylene behaved analogously, but vinyl-1,4-benzoquinone afforded only amorphous material.Diethyl (1,4-benzoquinonylmethyl)malonate gave ethyl 6-hydroxycoumarin-3-carboxylate when irradiated in benzene containing a trace of oxygen.The mechanistic significance of these results is discussed.

Light-induced and related reactions of quinones. Part V. Substituent effects in light-induced reactions between p-quinones and aldehydes

Irradiation of 1,4-benzoquinone with visible light in the presence of terephthaldehyde, p-cyanobenzaldehyde, and p-trifluoromethylbenzaldehyde yields the corresponding quinol monoaroyl esters as the major addition products. Similarly, naphthazarinquinone, 1,4-benzoquinone-2,3-dicarboxylic anhydride, and 2,3-dicyano-1,4-benzoquinone in acetaldehyde give the corresponding quinol monoacetates. 1,4-Benzoquinone gives quinol monoacrylate exclusively when it is irradiated in benzene containing acraldehyde, but in the presence of crotonaldehyde it yields both quinol monocrotonate and crotonylquinol. The significance of these results is discussed.

Light-induced and related reactions of quinones. Part VII. Cleavage and isomerisation of some (1-hydroxyalkyl)-1,4-benzoquinones

The synthesis is described of 1,4-benzoquinones carrying, severally, the following side-chains: CH(OH)·CH2Ph,CD(OH)·CH2Ph, CMe(OH)·CH2Ph, CH(OH)·CHPh2, CH(OH)·CH2·CH:CH2, and CMe(OH)·CH2·CH:CH2. When irradiated with visible light all the secondary alcohols yield 2,5-dihydroxybenzaldehyde, and all the tertiary alcohols give 2,5-dihydroxyacetophenone, probably via fragmentation of the derived alkoxyl radicals. The tertiary alcohols also yield isomers in which reorganisation of the side-chain has occurred. Mechanisms are suggested.

Light-induced cleavage of the side-chain of some 1′-hydroxyalkyl-1,4-benzoquinones

Light-induced fragmentation of 1′-hydroxy-alkyl-1,4-benzoquinones to acylquinols occurs when suitable free radical leaving groups are present at the 1′-position.