A convenient synthesis of quinolizinium salts through Rh(III) or Ru(II)-catalyzed C-H bond activation of 2-alkenylpyridines

Rhodium-catalyzed (5+1) annulations between 2-alkenylphenols and allenes: a practical entry to 2,2-disubstituted 2H-chromenes

Readily available alkenylphenols react with allenes under rhodium catalysis to provide valuable 2,2-disubstituted 2H-chromenes. The whole process, which involves the cleavage of one C-H bond of the alkenyl moiety and the participation of the allene as a one-carbon cycloaddition partner, can be considered a simple, versatile, and atom-economical (5+1) heteroannulation. The reaction tolerates a broad range of substituents both in the alkenylphenol and in the allene, and most probably proceeds through a mechanism involving a rhodium-catalyzed C-C coupling followed by two sequential pericyclic processes.

Rhodium(iii)-catalyzed cascade oxidative annulation reactions of aryl imidazolium salts with alkynes involving multiple C–H bond activation

The cascade oxidative annulation reactions of aryl imidazolium salts with alkynes proceed efficiently in the presence of [Cp*RhCl₂]₂ and Cu(OAc)₂·H₂O to give substituted imidazo[1,2-a]-quinolinium salts and benzo[ij]imidazo[2,1,5-de]quinolizinium salts.

Rhodium(III)-catalyzed dearomatizing (3 + 2) annulation of 2-alkenylphenols and alkynes

Appropriately substituted 2-alkenylphenols undergo a mild formal [3C+2C] cycloaddition with alkynes when treated with a Rh(III) catalyst and an oxidant. The reaction, which involves the cleavage of the terminal C–H bond of the alkenyl moiety and the dearomatization of the phenol ring, provides a versatile and efficient approach to highly appealing spirocyclic skeletons and occurs with high selectivity.

Rh(iii)-catalyzed synthesis of 1-substituted isoquinolinium salts via a C–H bond activation reaction of ketimines with alkynes

An efficient synthesis of highly substituted isoquinolinium salts from ketimines and alkynes via a Rh(iii)-catalyzed C–H bond activation and annulation reaction is described.

RhIII-catalyzed dual directing group assisted sterically hindered C–H bond activation: a unique route to meta and ortho substituted benzofurans

A new strategy for the synthesis of highly substituted benzofurans from meta-substituted hydroxybenzenes and alkynes via a rhodium(iii)-catalyzed activation of a sterically hindered C–H bond is demonstrated.

Straightforward assembly of benzoxepines by means of a rhodium(III)-catalyzed C-H functionalization of o-vinylphenols

Readily available o-vinylphenols undergo a formal (5 + 2) cycloaddition to alkynes when treated with catalytic amounts of [Cp*RhCl2]2 and Cu(OAc)2. The reaction, which involves the cleavage of the terminal C-H bond of the alkenyl moiety, generates highly valuable benzoxepine skeletons in a practical, versatile, and atom-economical manner. Using carbon monoxide instead of an alkyne as reaction partner leads to coumarin products which formally result from a (5 + 1) cycloaddition.

Synthesis of isoquinolines via Rh(III)-catalyzed C-H activation using hydrazone as a new oxidizing directing group

An efficient and mechanistically interesting method for the synthesis of highly substituted isoquinolines by a Rh(III)-catalyzed hydrazone directed ortho C-H bond activation and annulation without an external oxidant is described. This reaction is accomplished via a C-C and C-N bond formation along with N-N bond cleavage.