Synthesis of polyoxygenated hydrocarbons via radical-mediated oxygenation of vinylcyclopropanes

Stereoselective Photoredox Catalyzed (3+3) Dipolar Cycloaddition of Nitrone with Aryl Cyclopropane

By resorting to the principle of remote activation, we herein demonstrate the first photoredox catalyzed (3+3) dipolar cycloaddition of nitrones with aryl cyclopropanes. Key to the fidelity of the reaction resides in a facile manner of substrate activation by single-electron transfer (SET) oxidation with photoredox catalysis, and the reaction takes place through a stepwise cascade encompassing a three-electron-type nucleophilic substitution triggered cyclopropane ring-opening and a diastereoselective 6-endo-trig radical cyclization manifold. The reaction proceeds under mild conditions with excellent regio- and stereoselectivity, nicely complementing the well-developed Lewis acid catalyzed cycloaddition of donor-acceptor cyclopropanes. Other merits of the protocol include wide scope of aryl cyclopropanes with diversified substitution patterns and good functional-group compatibility. A mechanism involving an aryl radical cation promoted remote activation mode was also proposed and supported by mechanistic experiments.

Electrocatalytic Activation of Donor-Acceptor Cyclopropanes and Cyclobutanes: An Alternative C(sp3 )-C(sp3 ) Cleavage Mode

We describe the first electrochemical activation of D-A cyclopropanes and D-A cyclobutanes leading after C(sp3 )-C(sp3 ) cleavage to the formation of highly reactive radical cations. This concept is utilized to formally insert molecular oxygen after direct or DDQ-assisted anodic oxidation of the strained carbocycles, delivering β- and γ-hydroxy ketones and 1,2-dioxanes electrocatalytically. Furthermore, insights into the mechanism of the oxidative process, obtained experimentally and by additional quantum-chemical calculations are presented. The synthetic potential of the reaction products is demonstrated by diverse derivatizations.

Metal-hydride hydrogen atom transfer (MHAT) reactions in natural product synthesis

Functionalization of olefins has been an important transformation in synthetic chemistry. This review will focus on the natural product synthesis employing the MHAT reaction as the key strategy.

Iodine-Catalyzed Aerobic Oxidation of Spirovinylcyclopropyl Oxindoles to Form Spiro-1,2-dioxolanes Diastereoselectively

A novel method of iodine-catalyzed aerobic oxidation with spirovinylcyclopropyl oxindoles under mild conditions has been described. A series of spiro-1,2-dioxolanes were prepared in good to excellent yields and considerable diastereoselectivities. The new approach is operationally simple, scalable, and tolerant of various functional groups.

Structural diversity and chemical synthesis of peroxide and peroxide-derived polyketide metabolites from marine sponges

The structural elucidation, chemical synthesis and therapeutic potential of peroxide and peroxide-derived sponge metabolites, with special focus on their intriguing structural similarities and differences from a biogenetic perspective, are reviewed.

Asymmetric synthesis of 3,3,5,5-tetrasubstituted 1,2-dioxolanes: total synthesis of epiplakinic acid F

The first enantioselective total synthesis of epiplakinic acid F (1) was achieved through a pivotal step involving a radical-mediated asymmetric peroxidation of vinylcyclopropanes with molecular oxygen to construct highly substituted 1,2-dioxolanes.

Total synthesis of plakortide E and biomimetic synthesis of plakortone B

The total synthesis of plakortide E (1a) is reported. A novel palladium-catalyzed approach towards 1,2-dioxolanes as well as an alternative substrate-controlled route leading exclusively to cis-highly substituted 1,2-dioxolanes have been developed. A lipase-catalyzed kinetic resolution was employed to provide optically pure 1,2-dioxolane central cores. Coupling of the central cores and side chains was achieved by a modified Negishi reaction. All four isomeric structures of plakortide E methyl ester, namely, 26a-d were synthesized. One of the structures, 26d, was shown to be identical with the natural plakortide E methyl ester on the basis of (1)H, (13)C NMR spectra and specific rotation comparisons. With the plakortide E methyl ester (4S,6R,10R)-(-)-cis-26d and its other three isomers in hand, we successfully converted them into (3S,4S,6R,10R)-plakortone B (2a), and its isomers ent-2a, 2b and ent-2b via an intramolecular oxa-Michael addition/lactonization cascade reaction. Finally, saponification converted 1,2-dioxolane 26d into plakortide E (1a) whose absolute configuration (4S,6R,10R) was confirmed by comparison of spectral and physical data with those reported.