Ru-Catalyzed Carbonylative Murai Reaction: Directed C3-Acylation of Biomass-Derived 2-Formyl Heteroaromatics

The Murai reaction is a ruthenium-catalyzed transformation leading to alkylated arenes through the C 12C bond formation between an alkene and an arene bearing a directing group. Discovered in the nineties, this useful C 12H activation based coupling has been the object of intense study since its discovery. After having studied the Murai reaction on 2-formylfurans of biomass derivation, we describe here the carbonylative version applied to 2-formylfurans, 2-formylpyrrols and 2-formylthiophenes. This acylation reaction takes place regioselectively at C3 position of the heterocyclopentadienes thanks to the installation of removable imine directing groups. The transformation can be achieved by treating the two reaction partners with a catalytic amount of Ru3(CO)12, in toluene at 120\u2013150 \ub0C, after CO bubbling, at atmospheric pressure. DFT computations of the full catalytic cycle help in deciphering the mechanism of this transformation, and to rationalize the different behaviors depending on the nature of imine directing groups. (Figure presented.)

Pd-Catalyzed Direct C–H Alkenylation and Allylation of Azine <i>N</i>‑Oxides

A Pd-catalyzed direct C₂-alkenylation of azine <i>N</i>-oxides with allyl acetate is disclosed. The products are formed through an allylation/isomerization cascade process. The use of a tri-<i>tert</i>-butylphosphonium salt as the ligand precursor and KF is mandatory for optimal yields. When cinnamyl acetate is used, the same catalytic system promotes C₂-cinnamylation of the azine <i>N</i>-oxide without subsequent isomerization. A mechanism is proposed on the basis of experimental studies and DFT calculations

Improved simplicity and practicability in copper-catalyzed alkynylation of tetrahydroisoquinoline

Alkynylation reactions of N-protected tetrahydroisoquinolines have been performed using several different protocols of cross dehydrogenative coupling. Initially, a CuCl-catalyzed method was investigated, which worked well with three different N-protecting groups, namely phenyl, PMP, and benzyl and t-BuOOH as oxidant in acetonitrile as solvent. The peroxide could then be replaced by simple air and acetonitrile for water, leading to an overall very environmentally friendly protocol. Finally, a decarboxylative alkynylation protocol starting from alkynoic acids was also developed using again air as oxidant. This avoids the use of gaseous alkynes in the introduction of short-chained alkyne substituents.Austrian Science Foundation (FWF)911041