Organophotocatalytic\nReduction of Benzenes to Cyclohexenes

The reduction of\nabundant benzene rings to scarce C(sp<sup>3</sup>)-rich motifs is\ninvaluable for drug design, as C(sp<sup>3</sup>)\ncontent is known to correlate with clinical success. Cyclohexenes\nare attractive targets, as they can be rapidly elaborated into large\nproduct libraries and are stable against rearomatization. However,\npartial reduction reactions of benzenes to cyclohexenes are rare and\nhave a very narrow scope. Herein we report a broadly applicable method\nthat converts electron-poor benzenes to cyclohexenes and tolerates\nLewis-basic functional groups such as triazoles and thioethers as\nwell as reducible groups such as cyanides, alkynes, and sulfones.\nThe reaction utilizes an organic donor that induces mild arene reduction\nby preassociation to a photoexcitable electron donor–acceptor\n(EDA) complex and mild isomerization of redox-inert 1,4-cyclohexadienes\nto reducible 1,3-cyclohexadienes without a strong base in its oxidized\nthioquinone methide form.