Palladium-Catalyzed Synthesis of Functionalized Indoles by Acylation/Allylation of 2-Alkynylanilines with Three-Membered Rings.

Palladium-catalyzed synthesis of 3-acyl and -allyl indoles has been realized by merging nucleophilic cyclization of ortho-alkynylanilines with ring opening of three-membered rings such as cyclopropenones and gem-difluorinated cyclopropanes. These functionalized indoles were obtained in moderate to high yields with high stereoselectivity in both cases. This protocol provides an alternative method toward functionalized indoles under mild and redox-neutral conditions.

Occurrence and biosynthesis of plant sesterterpenes (C25), a new addition to terpene diversity.

Terpenes, the largest group of plant-specialized metabolites, have received considerable attention for their highly diverse biological activities. Monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), and triterpenes (C30) have been extensively investigated at both the biochemical and molecular levels over the past two decades. Sesterterpenes (C25), an understudied terpenoid group, were recently described by plant scientists at the molecular level. This review summarizes the plant species that produce sesterterpenes and describes recent developments in the field of sesterterpene biosynthesis, placing a special focus on the catalytic mechanism and evolution of geranylfarnesyl diphosphate synthase and sesterterpene synthase. Finally, we propose several questions to be addressed in future studies, which may help to elucidate sesterterpene metabolism in plants.

Rhodium(III)-Catalyzed Asymmetric [4+1] and [5+1] Annulation of Arenes and 1,3-Enynes: A Distinct Mechanism of Allyl Formation and Allyl Functionalization.

We report chiral RhIII cyclopentadienyl-catalyzed enantioselective synthesis of lactams and isochromenes through oxidative [4+1] and [5+1] annulation, respectively, between arenes and 1,3-enynes. The reaction proceeds through a C-H activation, alkenyl-to-allyl rearrangement, and a nucleophilic cyclization cascade. The mechanisms of the [4+1] annulations were elucidated by a combination of experimental and computational methods. DFT studies indicated that, following the C-H activation and alkyne insertion, a RhIII alkenyl intermediate undergoes δ-hydrogen elimination of the allylic C-H via a six-membered ring transition state to produce a RhIII enallene hydride intermediate. Subsequent hydride insertion and allyl rearrangement affords several rhodium(III) allyl intermediates, and a rare RhIII η4 ene-allyl species with π-agostic interaction undergoes SN2 '-type external attack by the nitrogen nucleophile, instead of C-N reductive elimination, as the stereodetermining step.