- Photochemical rearrangements of quinone monoketals
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We have studied the photochemistry of over 15 quinone cyclic monoketals, which were prepared by diol exchange from the dimethyl ketals, Swanton oxidation/hydrolysis, or direct ketalization. Their reactions in acidic media are generally explained by the classical mechanism for cyclohexadienone photochemical (di-π-methane) rearrangements: photocyclization to a cyclopropane-oxyallylcation that is protonated, followed by sovolysis. This reaction pathway provides, after hydrolysis, β-carboxy-substituted cyclopentenones. With a substituent at the β-position of the quinone monoketal, rearrangement selectivity is modestly in favor of the more substituted alkene product. With a substituent at the α-position of the quinone monoketal, rearrangement selectivity is strongly in favor of the less substituted alkene product. Possible mechanistic reasoning to explain these observations is offered.
- Pirrung, Michael C.,Nunn, David S.
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p. 5707 - 5738
(2007/10/03)
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