Palladium-catalyzed allylic C-H silylation was performed with use of hexamethyldisilane as the silyl source. These C-H functionalization reactions occur only in the presence of hypervalent iodine reagents or other strong oxidants and proceed with excellent regioselectivity, providing the linear allylic isomer of the allylsilane products. In demonstrating the first oxidative allylic C-H silylation of alkenes, this study marks an important advance for the catalytic C-H functionalization method.

The mechanism of the palladium-catalyzed synthesis of allylic silanes and boronates from allylic alcohols was investigated. (1)H, (29)Si, (19)F, and (11)B NMR spectroscopy was used to reveal key intermediates and byproducts of the silylation reaction. The tetrafluoroborate counterion of the palladium catalyst is proposed to play an important role in both catalyst activation as well as the transmetalation step. We propose that BF(3) is generated in both processes and is responsible for the activation of the substrate hydroxyl group. An (η(3)-allyl)palladium complex has been identified as the catalyst resting state, and the formation of (η(3)-allyl)palladium complexes directly from allylic alcohols has been studied. Kinetic analysis provides evidence that the turnover limiting step is the transmetalation, and insights into notable similarities between the borylation and the silylation reaction mechanisms enabled us to considerably improve the stereoselectivity of the borylation.

Palladium pincer complexes directly catalyze the redox coupling reactions of functionalized alkenes and iodonium salts. The catalytic process, which is suitable for mild catalytic functionalization of allylic acetates and electron-rich alkenes, probably occurs through Pd(IV) intermediates. Due to the strong metal-ligand interactions, the oxidation of phosphine and amine ligands of the pincer complexes can be avoided in the presented reactions.

Copper-mediated trifluoromethylation of allylic chlorides and trifluoroacetates was performed using a convenient Cu-CF3 reagent. The reaction is suitable for selective synthesis of allyl trifluoromethyl species. Mechanistic studies indicate that the reaction proceeds via a nucleophilic substitution mechanism involving allyl copper intermediates. The analogous Cu-F reagent was suitable for fluorination of allyl chlorides. Stereodefined cyclic substrates reacted regio- and stereoselectively.

Human dihydroorotate dehydrogenase (DHODH), an enzyme in the de novo pyrimidine synthesis pathway, is a target for the treatment of rheumatoid arthritis and multiple sclerosis and is re-emerging as an attractive target for cancer therapy. Here we describe the optimization of recently identified tetrahydroindazoles (HZ) as DHODH inhibitors. Several of the HZ analogues synthesized in this study are highly potent inhibitors of DHODH in an enzymatic assay, while also inhibiting cancer cell growth and viability and activating p53-dependent transcription factor activity in a reporter cell assay. Furthermore, we demonstrate the specificity of the compounds toward the de novo pyrimidine synthesis pathway through supplementation with an excess of uridine. We also show that induction of the DNA damage marker γ-H2AX after DHODH inhibition is preventable by cotreatment with the pancaspase inhibitor Z-VAD-FMK. Additional solubility and in vitro metabolic stability profiling revealed compound 51 as a favorable candidate for preclinical efficacy studies.