Synthetic and Mechanistic Studies on the Rhodium-Catalyzed Redox Isomerization of Cyclohexa-2,5-dienols

We report the application of cyclohexa-2,5-dienols in a catalytic redox isomerization: a rhodium-catalyzed desymmetrization for the synthesis of γ,γ-disubstituted cyclohexenones. The reaction generates products which are useful intermediates in organic synthesis, and its functional group tolerance compares favorably to that of classical redox isomerizations. Through deuteration, crossover, and competition experiments, the mechanism was found to involve an intramolecular 1,3-hydride shift. The enantioselective version of the reaction was also studied

Total Synthesis of (<i>R</i>)‑Sarkomycin via Asymmetric Rhodium-Catalyzed Conjugate Addition

(<i>R</i>)-Sarkomycin was prepared using a five-step total synthesis. Key steps in the enantioselective construction of the targeted scaffold were a rhodium-catalyzed asymmetric conjugate alkenyl addition with subsequent silyl trapping and a Mukaiyama aldol reaction with aqueous formaldehyde. Protection of the hydroxy group as a THP acetal and oxidative cleavage of the C,C-double bond provided a stable direct precursor to the natural product. The final liberation was carried out under slightly acidic conditions in a microwave-assisted reaction, resulting in a high yield of the “deceptive” sarkomycin. This represents the shortest enantioselective synthesis of this rather unstable compound to date and the first to employ asymmetric catalysis to introduce the stereogenic center

Employing Pd-Catalyzed C–H Arylation in Multicomponent-Multicatalyst Reactions (MC)²R: One-Pot Synthesis of Dihydrobenzoquinolines

The one-pot synthesis of a broad variety of dihydrofuroquinolines, dihydrothienoquinolines, and dihydrobenzoquinolines is reported. The combination of the Rh­(I)-catalyzed hydroarylation of vinylpyridines with the Pd(0)/Pd­(II)-catalyzed direct C–H arylation in a Multicomponent-Multicatalyst Reaction (MC)²R could be used to develop an efficient and step-economic protocol for the rapid construction of molecular complexity. A high-yielding synthesis of π-extended heteroarenes through an efficient three-step-one-pot procedure and a highly enantioselective synthesis of 6-alkylsubstituted dihydrobenzoquinolines are shown