Dihydropyrrolo[1,2-b]pyrazoles: withasomnine and related compounds

In the paper we indicate the increasing importance of derivatives containing a dihydropyrrolo[1,2-b]pyrazole (DPP) core. We try to show our synthetic approach based on an improved Kulinkovich method as well as our new synthetic pathway. A complex methodology involving the preparation of substituted DPPs focuses on withasomnine and the synthesis of several structurally related compounds. The developed reaction protocols enable the preparation of the mentioned bicyclic system with broadly diverse substitution. Thus, we are able to prepare systems with aliphatic, aromatic, polyaromatic, heteroaromatic, TMS, and even adamantane substitution with known biologically active properties. The reaction protocol, consisting of two multi-step synthetic pathways, includes Sonogashira and Suzuki–Miyaura cross-coupling reactions, allenyl synthon formation, Kulinkovich cyclopropanation, ring transformations, and nonsymmetrical homoallenyl azines cycloadditions. Moreover, we prepared compounds with a resemblance to other bioactive species: fadrozole, nagstatine, an antitumor agent LY2109761 and a mixed lineage kinase 7 inhibitor DHP-2.