Coniferyl alcohol, flash photolysis

Irradiation of 2,2-dimethyl chromene through Pyrex using a 550-W Hanovia lamp initiates a retro 4 + 2 reaction to form the extended quinone methide 4, which reacts with methanol to form a pair of methyl ethers (Scheme 6A).18 Flash photolysis of coniferyl alcohol 5 generates the quinone methide 6 (Scheme 6B) by elimination of hydroxide ion from the excited-state reaction intermediate.19 The kinetics for the thermal reactions of 6 in water were characterized,20 but not the reaction products. These were assumed to be the starting alcohol 5 from 1,8-addition of water to 6 and the benzylic alcohol from 1,6-addition of water (Scheme 6). A second quinone methide has been proposed to form as a central intermediate in the biosynthesis of several neolignans,21a and chemical synthesis of neolignans has been achieved... 

Flash photolysis of coniferyl alcohol in water and in acetic acid produces a transient species with at 350 nm [147]. It decays by first-order kinetics in both solvents, but with very different lifetimes 500 s in water and 1.2 s in acetic acid. The transient is unreactive toward oxygen. Based on this reactivity pattern, Leary [147] assigned this transient as the corresponding quinone methide. Although this initial experiment used a flash-photolysis setup, the quinone methide is sufficiently long-lived that it can be detected with a modern UV-visible spectrophotometer using diode-array detection [148]. 

G Leary, Flash Photolysis of Coniferyl Alcohol. Chem. Comm. 13 688-689, 1971. 

Wan and his co-workers have reported the photohydration and photosolvolysis of the alkenes (45). The reactions involve the intermediacy of quinone-methide type intermediates. Flash photolysis of coniferyl alcohol (46) and isoeugenol (47) in acetonitrile has supplied evidence for the formation of the corresponding radical cations. These transient species react readily with water and other hydroxylic solvents to afford 4-vinylphenoxyl radicals. ... 

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