Synthesis of Pyrazolo[1,2‐a]cinnolines via Rhodium(III)‐Catalyzed [4+2] Annulation Reactions of Pyrazolidinones with Sulfoxonium Ylides

Abstract

A method to synthesize pyrazolo[1,2‐a]cinnolines via rhodium(III)‐catalyzed C−H activation of pyrazolidinones and subsequent [4+2] annulation of sulfoxonium ylides was developed. 5‐Substituted or 5,10‐disubstituted pyrazolo[1,2‐a]cinnolines could be obtained by slightly adjusting the reaction conditions. Gram‐scale synthesis and practical transformations proved the practicability of this method. The mechanism of this method was proposed in the article on the basis of preliminary mechanistic results and previous reports. This method features simplified operation, metal‐oxidant free, and readily available reactants.

α-Carbonyl sulfoxonium ylides in transition metal-catalyzed C–H activation: a safe carbene precursor and a weak directing group

“…Wang's group 46 demonstrated the construction of pyrazolo[1,2- a ]cinnolines 113 by Rh( iii )-catalyzed annulation of pyrazolidinones 112 with sulfoxonium ylides (Scheme 42). The corresponding dehydration products 114 were easily obtained using TFA in one pot synthesis.…”

Non-Palladium-Catalyzed Approach to the Synthesis of (E)-3-(1,3-Diarylallylidene)Oxindoles

“…The difference in reaction rate may have been caused by the lithiated intermediate from (E)-5a assuming a stable chelated form via coordination of the oxindole carbonyl group. Dehydration of 8aa proceeded smoothly under acidic conditions to provide 3aa in 95% yield [27,28]. Next, we examined whether the second stepwise approach (aldol/dehydration) was applicable to 5d (Table 3).…”

Copper-Catalyzed [4＋2] Annulations of Sulfoxonium Ylides and o-Phenylenediamines

“…For example, Wu's group [24f] reported the Rh-catalyzed [1＋5] and [1＋4] cycloaddition of sulfoxonium ylides with N-arylamidines for the synthesis of indoles and quinazolines. Additionally, Liu and coworkers [29] accomplished the application of sulfoxonium ylides as two carbon synthons for the preparation of pyrazolo [1,2-a]cinnolines. However, expensive and detrimental metal catalysts, comparatively harsh reaction conditions limited the wide application of sulfoxonium ylides in organic synthesis.…”