Domino Reaction of Arylglyoxals with Pyrazol-5-amines: Selective Access to Pyrazolo-Fused 1,7-Naphthyridines, 1,3-Diazocanes, and Pyrroles

New
multicomponent domino reactions of arylglyoxals with pyrazol-5-amines
have been established, providing selective access to unprecedented
pyrazolo-fused 1,7-naphthyridines, 1,3-diazocanes, and pyrroles (up
to 52 examples). The unreported dipyrazolo-fused 1,7-naphthyridines
were regioselectively synthesized through a special double [3 + 2
+ 1] heteroannulation accompanied by direct C–C formation between
two electrophilic sites of arylglyoxals. The unusual [3 + 3 + 1 +
1] cyclization resulted in 20 examples of novel dipyrazolo-fused 1,3-diazocanes,
whereas pyrrolo­[2,3-c]­pyrazoles were obtained in
good yields by varying arylglyoxals 1 and pyrazol-5-amines 2 in the ratio 1:2. Mechanisms of formation of these three
new types of heterocycles are also proposed.