Synthesis and DFT analysis of non-covalent interactions in crystal structures of 6-R-2-alkoxy-, 2,3-di-, and 2,2,3-tri-tert-butylpyrrolo[1,2-b][1,2,4]triazines

Novel 7-amino-3-tert-butyl-2-OR1-6-R2-pyrrolo[1,2-b][1,2,4]triazine-8-carbonitriles (R1 = CH2CO2Et, CH2Boc, Me, n-Bu; R2 = CO2Et, CO2 n-Bu, CO2 t-Bu, C6H4CO2 i-Pr) have been synthesized and investigated by X-ray diffraction. Nucleophilic replacement of an alkoxy group with t-BuLi afforded sterically hindered tert-butyl 7-amino-2,3-di-tert-butyl- and 2,2,3-tri-tert-butyl-8-cyanopyrrolo[1,2-b][1,2,4]triazine-6-carboxylates. The lengths and bond angles as well as packing modes of molecules in crystals have been considered. The non-covalent interactions such as the changes in the H-bonding and close contacts were analyzed by DFT and the Hirshfeld surfaces and compared for different substituents.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11224-022-02006-x.

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.