Stereoselective Palladium-Catalyzed Arylation of Exo-Glycals with Aryl Iodides

Skeletal Transformations of Terpenoid Forskolin Employing an Oxidative Rearrangement Strategy

The skeletal transformations of diterpenoid forskolin were achieved by employing an oxidative rearrangement strategy. A library of 36 forskolin analogues with structural diversity was effectively generated. Computational analysis shows that 12 CTD compounds with unique scaffolds and ring systems were produced during the course of this work.

Synthesis of C,N-Glycosides via Brønsted Acid-Catalyzed Azidation of exo-Glycals

The reaction of exo-glycals with azidotrimethylsilane in the presence of a Brønsted acid leads to the generation of the corresponding C,N-glycosyl azides. The majority of these glycosylation reactions proceed at room temperature with short reaction times. In addition, the targeted products were obtained in high yields with exclusive diastereoselectivity to the α-anomer in pyranose-based derivatives. Carbohydrate units based on mannose, galactose, arabinose, and ribose were also shown to proceed in high yields.

Synthesis of Five-Membered exo-Glycals from Six-Membered 2-Iodo-endo-glycals

Five-membered exo-glycals were synthesized from six-membered 2-iodo-endo-glycals by a metal/halogen exchange/ring-opening sequence followed by a cyclization catalyzed by Ag₂CO₃.

Direct nucleophilic and electrophilic activation of alcohols using a unified boron-based organocatalyst scaffold

Organocatalytic strategies for the direct activation of hydroxy-containing compounds have paled in comparison to those applicable to carbonyl compounds. To this end, boronic acids have emerged as valuable catalysts for the functionalization of hydroxy groups in a mild and selective fashion. Distinct modes of activation in boronic acid-catalyzed transformations are often accomplished by vastly different catalytic species, complicating the design of broadly applicable catalyst classes. Herein, we report the use of benzoxazaborine as a general scaffold for the development of structurally related yet mechanistically divergent catalysts for the direct nucleophilic and electrophilic activation of alcohols under ambient conditions. The utility of these catalysts is demonstrated in the monophosphorylation of vicinal diols and the reductive deoxygenation of benzylic alcohols and ketones respectively. Mechanistic studies of both processes reveal the contrasting nature of key tetravalent boron intermediates in the two catalytic manifolds.

Synthesis of intramolecular cross-coupling analogues of forskolin

A ring distortion strategy was applied to the synthesis of a series of intramolecular cross-coupled analogues of forskolin 1. Treatment with palladium acetate, forskolin underwent an intramolecular cross-coupling reaction to generate a novel cycloalkene ether 2 in 85% yield. Under the same conditions, a series of forskolin ester analogues 4a-4d were prepared from 1-OH ester derivatives of forskolin 3a-3d in 85-93% yields. Treating cycloalkene ether 2 with aryl iodides in the presence of a palladium catalyst afforded Z-isomers arylation products 5a-5e in a stereoselective manner in 70-85% yields.