Synthesis and NMR spectroscopy (1H 13C) of 1-(2′-benzothiazolyl)-3(5),4-polymethylenepyrazoles and related compounds

A series of 3(5),4-trimethylene and 3(5),4-tetramethylenepyrazoles (tetrahydroindazoles) have been prepared from 2-acylcyclanones using two methods: direct reaction with a substituted hydrazine and through an NH-pyrazole followed by nucleophilic substitution. The results mainly concern the 2-benzothiazolyl substituent, but 2,4-dinitrophenyl derivatives were also studied for comparison. The orientation of the reactions (isomer ratio), the deshielding in ¹H nmr of the 5-methyl and 5-methylene signals when a benzothiazolyl residue is at position 1, and the ring strain effect on heterocyclic carbons chemical shifts, are discussed.