A sulfenium-ion-initiated, catalytic, enantio-selective polyene cyclization is described. Homogeranylar-enes and ortho-geranylphenols undergo polycyclization in good yield, diastereoselectivity, and enantioselectivity. The stereodetermining step is the generation of an enantio-merically enriched thiiranium ion from a terminal alkene and a sulfenylating agent in the presence of a chiral Lewis basic catalyst. The use of hexafluoroisopropyl alcohol as the solvent is crucial to obtain good yields. The thioether moiety resulting from the reaction can be subsequently transformed into diverse oxygen and carbon functionality postcyclization. The utility of this method is demonstrated by the enantioselective syntheses of (+)-ferruginol and (+)-hinokiol.

We report here a catalytic method for the modular ring expansion of cyclic aliphatic alcohols. In this work, proton-coupled electron transfer (PCET) activation of an allylic alcohol substrate affords an alkoxy radical intermediate that undergoes subsequent C-C bond cleavage to furnish an enone and a tethered alkyl radical. Recombination of this alkyl radical with the revealed olefin acceptor in turn produces a ring-expanded ketone product. The regioselectivity of this C-C bondforming event can be reliably controlled via substituents on the olefin substrate, providing a means to convert a simple N-membered ring substrate to either n+1 or n+2 ring adducts in a selective fashion.

A light-driven method for the contra-thermodynamic positional isomerization of olefins is described. In this work, stepwise PCET activation of a more substituted and more thermodynamically stable olefin substrate is mediated by an excited-state oxidant and a Brønsted base to afford an allylic radical that is captured by a Cr(II) co-catalyst to furnish an allylchromium(III) intermediate. In situ protodemetalation of this allylchromium complex by methanol is highly regioselective and affords an isomerized and less thermodynamically stable alkene product. The higher oxidation potential of the less substituted olefin isomer renders it inert to further oxidation by the excited-state oxidant, enabling it to accumulate in solution over the course of the reaction. A broad range of isopropylidene substrates is accommodated, including enol ethers, enamides, styrenes, 1,3-dienes, and tetrasubstituted alkyl olefins. Mechanistic investigations of the protodemetalation step are also presented.

A method is described for the isomerization of acyclic allylic alcohols into β‐functionalized ketones via 1,3‐alkyl transposition. This reaction proceeds via light‐driven proton‐coupled electron transfer (PCET) activation of the O−H bond in the allylic alcohol substrate, followed by C−C β‐scission of the resulting alkoxy radical. The transient alkyl radical and enone acceptor generated in the scission event subsequently recombine via radical conjugate addition to deliver β‐functionalized ketone products. A variety of allylic alcohol substrates bearing alkyl and acyl migratory groups were successfully accommodated. Insights from mechanistic studies led to a modified reaction protocol that improves reaction performance for challenging substrates.

A light-driven method for the contra-thermodynamic positional isomerization of olefins is described. In this work, stepwise PCET activation of a more substituted and more thermodynami-cally stable olefin substrate is mediated by an excited-state oxi-dant and a Brønsted base to afford an allylic radical that is cap-tured by a Cr(II) co-catalyst to furnish an allylchromium(III) intermediate. In situ protodemetalation of this allylchromium complex by methanol is highly regioselective and affords an isomerized and less thermodynamically stable alkene product. The higher oxidation potential of the less substituted olefin isomer renders it inert to further oxidation by the excited-state oxidant, enabling it to accumulate in solution over the course of the reaction. A broad range of isopropylidene substrates is ac-commodated, including enol ethers, enamides, styrenes, 1,3-dienes, and tetrasubstituted alkyl olefins. Mechanistic investiga-tions of the protodemetalation step are also presented.