Synthesis of Substituted Pyrimido[1,2-b]indazoles through (3+2+1) Cyclization of 3-Aminoindazoles, Ketones, and N,N-Dimethylaminoethanol as One-Carbon Synthon

2-Mono- or 2,3-disubstituted pyrimido[1,2-b]indazoles are synthesized by a (3+2+1) three-component cyclization of 3-aminoindazoles, ketones, and N,N-dimethylaminoethanol as a methine source. The reaction demonstrates good tolerance of both aromatic and aliphatic ketones, as well as various substitution patterns in air. A plausible mechanism is discussed.