Forskolin Editing via Radical Iodo- and Hydroalkylation

The modification of highly oxygenated forskolin as well as manoyl and epi-manoyl oxide, two less functionalized model substrates sharing the same polycyclic skeleton, via intermolecular carbon-centered radical addition to the vinyl moiety has been investigated. Highly regio- and reasonably stereoselective iodine atom transfer radical addition (ATRA) reactions were developed. Unprotected forskolin afforded an unexpected cyclic ether derivative. Protection of the 1,3-diol as an acetonide led the formation of the iodine ATRA product. Interestingly, by changing the mode of initiation of the radical process, in situ protection of the forskolin 1,3-diol moiety as a cyclic boronic ester took place during the iodine ATRA process without disruption of the radical chain process. This very mild radical-mediated in situ protection of 1,3-diol is expected to be of interest for a broad range of radical and non-radical transformations. Finally, by using our recently developed tert-butyl­catechol-mediated hydroalkylation procedure, highly efficient preparation of forskolin derivatives bearing an extra ester or sulfone group was achieved.

Thiyl Radicals: Versatile Reactive Intermediates for Cyclization of Unsaturated Substrates

Sulfur centered radicals are widely employed in chemical synthesis, in particular for alkene and alkyne hydrothiolation towards thioether bioconjugates. The steadfast radical chain process that enables efficient hydrothiolation has been explored in the context of cascade reactions to furnish complex molecular architectures. The use of thiyl radicals offers a much cheaper and less toxic alternative to the archetypal organotin-based radical methods. This review outlines the development of thiyl radicals as reactive intermediates for initiating carbocyclization cascades. Key developments in cascade cyclization methodology are presented and applications for natural product synthesis are discussed. The review provides a chronological account of the field, beginning in the early seventies up to very recent examples; a span of almost 50 years.

Migratory Reductive Cross-Coupling via Dual Nickel Metathesis

<div>Cross-electrophile coupling has been developed into a practical approach for the construction of carbon-</div><div>carbon bonds, wherein nickel catalysis has been widely employed. Mechanistically, a catalytic cycle involving</div><div>sequentially selective oxidative addition or radical chain process is proposed. Although the catalytic cycle of dual nickel metathesis has been discussed in several important works, none thinks this pathway is possible. In this manuscript, we present a thorough mechanistic study by a series of designed experiments toward the nickel-catalyzed migratory reductive cross-coupling. The results suggest that a catalytic cycle involving two organonickel(II) species metathesis as a key step, operates in this reaction. Moreover, we provide a discussion on the difference between the nickel-catalyzed migratory reductive cross-couplings and the classical ones. Additionally, based on the mechanistic finding, a new catalytic system has also been developed, which allows the use of electron-deficient aryl halides as starting materials, affording the migratory cross-coupling products efficiently.</div>

Migratory Reductive Cross-Coupling via Dual Nickel Metathesis

<div>Cross-electrophile coupling has been developed into a practical approach for the construction of carbon-</div><div>carbon bonds, wherein nickel catalysis has been widely employed. Mechanistically, a catalytic cycle involving</div><div>sequentially selective oxidative addition or radical chain process is proposed. Although the catalytic cycle of dual nickel metathesis has been discussed in several important works, none thinks this pathway is possible. In this manuscript, we present a thorough mechanistic study by a series of designed experiments toward the nickel-catalyzed migratory reductive cross-coupling. The results suggest that a catalytic cycle involving two organonickel(II) species metathesis as a key step, operates in this reaction. Moreover, we provide a discussion on the difference between the nickel-catalyzed migratory reductive cross-couplings and the classical ones. Additionally, based on the mechanistic finding, a new catalytic system has also been developed, which allows the use of electron-deficient aryl halides as starting materials, affording the migratory cross-coupling products efficiently.</div>