Regioselective Construction and Screening of 1,3-Disubstituted Tetrahydroindazolones in Enantiomerically Pure Pairs

In this paper, we describe a regioselective synthetic pathway for enantiopure 1,3-disubstituted tetrahydroindazolone derivatives via the condensation of 2-acylcyclohexane-1,3-dione with various alkyl- and arylhydrazines using the steric effects of a Boc-protected pyrrolidine ring. This synthetic method has a broad scope for substrate generality for various hydrazines with excellent regioselectivity. To maximize the molecular diversity, further diversifications of 1,3-disubstituted tetrahydroindazolones were pursued by systematic <i>N</i>-modification of the secondary amine of the pyrrolidine ring using solution-phase parallel synthesis with polymer-supported reagents. A library containing a total of 272 drug-like tetrahydroindazolones, including 85 enantiomeric pairs, was constructed; the average purity, without further purification, was 95%