Rhodium(â…¢)-catalyzed Oxidative Coupling Of N-Allyl Arenesulfonamides With Alkynes

The modular assembly of regioselectively decorated heterocycles continues to be of central importance because of their prevalence in natural products, functional materials, crop protecting agents, or drugs. Contrast to the traditional methods, transition metal-catalyzed direct functionalization of C-H bonds pathway represents an efficient and atom-economic strategy.Cp*Rh complexes have been used increasingly in the past five years and stand out as highly active catalysts for C-H activation with high selectivity, broad substrate scope, and high functional-group compatibility. In chapter1, a review of C-H bond functionalization reactions has shown to introduce the background of synthesis chemistry about oxidative coupling between arenes and alkynes. At the end of this part, an protocol of my own experiments has made including significance, evidence, feasibility, and so on to grasp the whole article.Over the past five years,[RhCp*Cl2]2, have stood out as a highly efficient catalyst to mediate oxidative coupling between arenes and alkynes. Therefore, we report the efficient construction of pyridine and cyclopentanone rings in a Rh(III) catalyzed oxidative coupling of N-allyl sulfonamides with alkynes. Plenty of substrates were ready to demonstrate the vast applicability of this catalytic system. AgIoxidant is important in shifting the selectivity of the reaction. We propose a mechanism in which the cyclometalation of the substrate first affords a five-membered rhodacycle, which undergoes regioselective alkyne insertion to generate a seven-membered metallacycle. The fate of this metallacycle intermediate is determined by two possible pathways:intermediate undergoes C-N reductive elimination to give a dihydropyridine when a smaller amount of AgI is present; alternatively, in the presence of a larger amount of AgI, α,β-hydride-elimination pathway to afford a cyclometalated imine is preferred. This Intermediate should readily undergo migratory insertion of the alkenyl rhodium ligand into the N-Ts imine to afford a rhodium(Ⅲ) hydride species. A second β-hydrogen-atom elimination generates an imine E and a rhodium(Ⅲ) dihydride species, which can be oxidized to regenerate the RhⅢ active catalyst (4equivalents of AgI are needed). The final product could be formed from imine in a sequence involving the conjugate addition of water, followed by cyclopentadiene isomerization and ketone-enol tautomerization.