Ru(II)-Catalyzed and Ligand-Controlled C-H Activation and Annulation via 1,2-Phenyl Shift: Synthesis of Quaternary Carbon-Centered Pyrimidoindolones

Rh(III)-Catalyzed Switchable [4 + 1] and [4 + 2] Annulation of N-Aryl Pyrazolones with Maleimides: An Access to Spiro Pyrazolo[1,2-a]indazole-pyrrolidine and Fused Pyrazolopyrrolo Cinnolines

A rhodium(III)-catalyzed controllable [4 + 1] and [4 + 2] annulation of N-aryl pyrazolones with maleimides as C1 and C2 synthon has been explored for the synthesis of spiro[pyrazolo[1,2-a]indazole-pyrrolidines] and fused pyrazolopyrrolo cinnolines. The product selectivity was achieved through time-dependent annulation. The [4 + 1] annulation reaction involves sequential Rh(III)-catalyzed C-H alkenylation of N-aryl pyrazolone, followed by an intramolecular spirocyclization via aza-Michael-type addition to afford spiro[pyrazolo[1,2-a]indazole-pyrrolidine]. However, prolonged reaction time converts in situ formed spiro[pyrazolo[1,2-a]indazole-pyrrolidine] into fused pyrazolopyrrolocinnoline. This unique product formation switch proceeds via strain-driven ring expansion through a 1,2-shift of the C-C bond.

Electrochemical synthesis of versatile ammonium oxides under metal catalyst-, exogenous-oxidant-, and exogenous-electrolyte-free conditions

An electrochemical oxidative cross-coupling reaction between 2.5-substituted-pyrazolin-5-ones and ammonium thiocyanate has been developed, which resulted in a series of unprecedented cross-coupling products under metal catalyst-, exogenous-oxidant-, and exogenous-electrolyte-free conditions. It is worth noting that since the resulting cross-coupling products are nearly insoluble in MeCN, the pure product could be afforded without silica gel column purification. In addition, the prepared ammonium oxides are versatile building blocks for synthesizing functionalized pyrazole derivatives.

Synthesis of quaternary carbon-centered indolo[1,2-a]quinazolinones and indazolo[1,2-a]indazolones via C-H functionalization

An unprecedented Ru(ii)-catalyzed Csp2-H bond activation and annulation reaction of phenylindazolones with diaryl-substituted alkynes and dialkyl-substituted alkynes provided efficient routes for the construction of all-carbon quaternary-centered indolo[1,2-a]quinazolinones and quaternary carbon-centered indazolo[1,2-a]indazolones, respectively. The indolo[1,2-a]quinazolinones were fomed via Csp2-H activation, alkyne insertion and a 1,2-phenyl shift. Indazolo[1,2-a]indazolones were formed through a cascade reaction via the formation of exocyclic double bonds containing indolo[1,2-a]quinazolinones.

Metal-free tandem reaction synthesis of spiro-cyclopropyl fused pyrazolin-5-one derivatives

A highly efficient cascade annulation approach was developed for the synthesis of novel spiro-cyclopropyl fused pyrazolin-5-ones from pyrazole-3-ketone substrates and two-component sulfur ylides in an acidic environment.

Construction of pyrazolone analogues via rhodium-catalyzed C–H activation from pyrazolones and non-activated free allyl alcohols

Highly efficient rhodium(iii) catalysis was developed for obtaining structurally divergent pyrazolone analogues from pyrazolones and non-activated free allyl alcohols.