[4+2] or [4+1] Annulation: Changing the Reaction Pathway of a Rhodium‐Catalyzed Process by Tuning the Cp Ligand

Abstract

A change in reaction pathway was achieved for the first time by tuning the cyclopentadienyl (Cp) ligand used for the rhodium‐catalyzed cyclization of benzamides with conjugated enynones. Depending on the Cp ligand, the reaction pathway switched between [4+2] and [4+1] annulation. Electronic effects turned out to be crucial for the product distribution. The dichotomy was attributed to the alteration of the Lewis acidity of the resultant Cp‐bound rhodium species.

Cross‐Coupling of α‐Carbonyl Sulfoxonium Ylides with C−H Bonds

“…Significantly, the realization of this design would address the potential safety issues of the recently reported group-directed C À H functionalization reactions with diazo compounds [4] and their in situ precursors such as triazoles [5] or hydrazones. [6] Moreover, it would complement the scope of recently reported rhodium-catalyzed annulation reactions with cyclopropenes [7] and enynes, [8] reactions which also likely proceed by migratory insertion similar to the postulated evolution of D into E. Finally,itwould also expand the scope of the well-established CÀHinsertion chemistry of metal carbenoids generated from diazo compounds. [9] Herein, we show that a-carbonyl sulfoxonium ylides undergo efficient cross-coupling reactions with aC (sp 2 )ÀH bond of both arenes and heteroarenes in the presence of ar hodium catalyst, which does not require as acrificial oxidizing reagent.…”

Rhodium(III)‐Catalyzed Atroposelective Synthesis of Biaryls by C−H Activation and Intermolecular Coupling with Sterically Hindered Alkynes

“…Stoichiometric CÀHa ctivation of 1a with Rh-1 in the presence of AgOAc,followed by addition of PPh 3 ,a llowed isolation of the rhodacycle 11 in high yield (Scheme 7a). [17,18] Thecomplex 11 was characterized by NMR spectroscopy and X-ray crystallography (CCDC 1978298 contains the supplementary crystallographic data for this paper.T hese data can be obtained free of charge from The Cambridge Crystallographic Data Centre). In the crystal structure,the less hindered benzene ring of the benzamide is disposed toward the chiral ligand for minimized steric interactions,w hich sets up ac hiral environment for the incoming alkyne.…”

Rhodium(III)‐Catalyzed Atroposelective Synthesis of Biaryls by C−H Activation and Intermolecular Coupling with Sterically Hindered Alkynes

“…Stoichiometric CÀHa ctivation of 1a with Rh-1 in the presence of AgOAc,followed by addition of PPh 3 ,a llowed isolation of the rhodacycle 11 in high yield (Scheme 7a). [17,18] Thecomplex 11 was characterized by NMR spectroscopy and X-ray crystallography (CCDC 1978298 contains the supplementary crystallographic data for this paper.T hese data can be obtained free of charge from The Cambridge Crystallographic Data Centre). In the crystal structure,the less hindered benzene ring of the benzamide is disposed toward the chiral ligand for minimized steric interactions,w hich sets up ac hiral environment for the incoming alkyne.…”