Synthesis of 1,2,4-triazines and the triazinoisoquinolinedione DEF ring system of noelaquinone

CRYSTAL STRUCTURE OF 3-tert-BUTYL- PYRAZOLO[5,1-с][1,2,4]TRIAZINE-3,4-DIYL DICARBOXYLATES

By single crystal X-ray diffraction the structures of (trans-)7-R¹-8-methyl-3-tert-butyl-3,4-dihydropyrazolo[5,1-с][1,2,4]triazine-3,4-diyl dibenzoates 3а, 4а (R¹ = H, Br) and diacetate 3b (R¹ = H) are studied for the first time. The compounds are synthesized by oxidative bromination of respective 1,4-dihydropyrazolo[5,1-c][1,2,4]triazines in the presence of carboxylic acids. Dicarboxylates adopt a twist-conformation with the equatorial (3a) or axial (3b, 4a) orientation of tert-butyl groups relative to the heterocycle. In the case of diacetate 3b, a decrease in the thermal motion of the O4–C16–C17 fragment along with a decrease in the unit cell volume are observed on cooling from 300 K to 200 K. Bond lengths, torsion angles, and molecular packings in the crystals are discussed.

Natural Products with Heteroatom-Rich Ring Systems

This review focuses on all known natural products that contain a "heteroatom-rich" ring system, specifically a five-, six- or seven-membered ring that contains three or more heteroatoms. The isolation and biological activity of these natural products is discussed, along with the biosynthetic processes that Nature employs to assemble these rare heterocyclic frameworks.

A New Synthesis of 4,5,6,7-Tetrahydropyrazolo[1,5-c]pyrimidines by a Retro-Mannich Cascade Rearrangement

We discovered a new retro-Mannich reaction of in situ prepared pyrazolopyridines to give pyrazolopyrimidines that have hitherto been underrepresented in the heterocyclic chemistry literature. The isolation of a linear hydrolysis product supports a mechanistic hypothesis for this rearrangement process. In order to establish a broader access and explore potential biological applications for these medicinal chemistry building blocks, we investigated the scope of the reaction and generated small amine- as well as amide-based libraries through reductive aminations and amide couplings, respectively.

Natural products containing a nitrogen-nitrogen bond

As of early 2013, over 200 natural products are known to contain a nitrogen-nitrogen (N-N) bond. This report categorizes these compounds by structural class and details their isolation and biological activity.