Formation of fused ring junction N-heterocycles via Cp*Rh(III) imidoyl C–H activation

Fused [5,6]-heterocycles incorporating a ring-junction nitrogen have become increasingly important for numerous pharmaceutical applications with a myriad of targets. New synthetic methods to access these compounds from readily available starting materials have been developed. A one pot three component method to prepare pyrazolo[1,5-a]pyrimidines from aminopyrazoles, aldehydes, and sulfoxonium ylides is described. Further work to develop a method for the synthesis of azolopyridazines from hydrazones and alkynes is also explored. Both annulations utilize an imidoyl C–H activation by a Cp*Rh(III) catalyst to form a 5-membered rhodacycle as a key intermediate.