Ruthenium(II)-Catalyzed Regioselective [3 + 2] Spiroannulation of 2H-Imidazoles with 2-Alkynoates

Abstract

The CN double bond of 2H-imidazole has been employed as a C-electrophile for the ruthenium(II)-catalyzed [3 + 2] spiroannulation reaction of 4-phenyl-2H-imidazoles and 2alkynoates to synthesize spiroimidazole-4,1′-indenes. This strategy features high regioselectivity, broad functional group tolerance, and use of ruthenium as a catalyst, providing a new method to synthesize spirocycles with potential applications in pharmaceuticals.

Transition‐Metal‐Catalyzed Synthesis of Spiro Compounds through Activation and Cleavage of C−H Bonds

“…[38] Dai et al had successfully carried out Rh(III)-catalyzed annulation of olefins with diazooxindole to produce spirooxindole pyrrolone product. [39] Simply treating N (pivaloyloxy)acrylamides (90) and diazooxindoles (91) with [RhCp*Cl 2 ] 2 in MeCN, spirooxindoles were synthesized in very good yields (93, Scheme 22). Both aliphatic and aryl acrylamide substrates were transformed to chemoselective spirooxindole derivatives under base free conditions (In the presence of base like Cs 2 CO 3 produces a hydroxylated spiro compound).…”

“…[88] However, sequential annulation of the substrate first with alkyne and then with quinine provided generation of spiro-fused-isoquinolones (239, 241). [89] The formation of diannulation product with another alkyne is restricted by allowing the insertion under acidic conditions [90] which provides the formation of monoannulation product. The oxidizable MPS-DG regenerates the active catalyst.…”

2-Butyne Biscarbonate as a “Bridge” in Rhodium(III)-Catalyzed [4 + 2] Cyclization and Diels–Alder Reaction

“…It is well-known that conjugated diene provides opportunity for further chemical transformation (such as Diels–Alder reaction) to synthesize diverse structural polyheterocycles . In continuing our research on the green and efficient synthesis of heterocycles, herein we disclose a Rh­(III)-catalyzed cascade cyclization reaction of N -methoxybenzamides and 2-butyne biscarbonate, with or without maleimides (Scheme b). In this protocol, both two- and three-component [4 + 2 + 2] cyclizations proceeded smoothly to give variously fused heterocycles in a one-pot manner at room temperature with excellent regioselectivity and tolerated broad scope of substrates.…”

Formation of Fluorovinyl Spiro-[imidazole-indene] and α-Amino-β-naphthalenones via Rh(III)-Catalyzed Cascade C–H Functionalization

“…C–H activation tactics catalyzed by transition metals have evolved into one of the practical tools for assembling fluorine-containing compounds, in which conventional fluorinated building blocks were marked by trifluoromethyl diazos, gem-difluoroalkenes, gem-difluoroallyl, perfluoroalkenes, etc. In recent years, fluorinated alkynes have widely emerged as an indispensable coupling partner for the construction of fluorinated heterocycles in C–H activation, and transition metal-catalyzed [3+2] annulation via C–H activation has been considered one of the most powerful ways to synthesize heterocyclic compounds . In 2018, our group first employed 2 H -imidazoles in C–H activation, which afforded diverse annulations with versatile coupling partners .…”