Heterocyclic analogs of xanthiones: 5,6‐fused 3‐methyl‐1‐phenylpyrano[2,3‐c]pyrazol‐4(1H) thiones—synthesis and NMR (¹H, ¹³C, ¹⁵N) data

Abstract

Various [5,6]pyrano[2,3-c]pyrazol-4(1H)-thiones were synthesized in high yields by treatment of the corresponding [5,6]pyrano[2,3-c]pyrazol-4(1H)-ones with Lawesson's reagent. Detailed NMR spectroscopic studies were undertaken of the title compounds. Complete and unambiguous assignment of chemical shifts ((1)H, (13)C, (15)N) and coupling constants ((1)H,(1)H; (13)C,(1)H) was achieved by the combined application of various one- and two-dimensional (1D and 2D) NMR spectroscopic techniques. Unequivocal mapping of most (13)C,(1)H spin coupling constants is accomplished by 2D (delta, J) long-range INEPT spectra with selective excitation.

Heterocyclic Analogues of Xanthone and Xanthione. 1H-Pyrano[2,3-c:6,5-c]dipyrazol-4(7H)-ones and Thiones: Synthesis and NMR Data

“…In 5a this effect is much less pronounced leading to an upfield shift for C7a/C8a (δ 145.5 ppm) and a marked downfield shift for C3a/C4a (δ 117.8 ppm) compared to the appropriate shifts in 4a . Expectedly, C-4 suffers a distinct downfield shift (169.7 ppm → 192.1 ppm) when switching from 4a to 5a , the difference of 22.4 ppm is comparable with corresponding values found in related systems [36]. …”

“…Moreover, the corresponding thiones 5a , b and 5d - g are described. Considering that thio analogues of flavones, isoflavones, xanthones (= xanthione, Figure 1) and related systems have received considerable attention due to the importance of such molecules in biology and photochemistry [18], the latter systems 5 are interesting compounds in their own right as well [19,20]. …”

Applications of nuclear shielding

“…Complete and unambiguous assignment of chemical shifts ( 1 H, 13 C, 15 N) and coupling constants ( 1 H, 1 H; 13 C, 1 H) was achieved by the combined application of various one-and two-dimensional (1D and 2D) NMR spectroscopic techniques. 299 1 H, 13 C and 15 N NMR studies of gold(III), palladium(II) and platinum(II) chloride complexes with dimethylpyridines (lutidines: 2,3-lutidine, 2,3lut; 2,4-lutidine, 2,4lut; 3,5-lutidine, 3,5lut; 2,6-lutidine, 2,6lut) and 2,4,6-trimethylpyridine (2,4,6-collidine, 2,4,6col) having general formulas [AuLCl 3 ], trans-[PdL 2 Cl 2 ] and trans-/cis-[PtL 2 Cl 2 ] were performed and the respective chemical shifts (d 1H , d 13C , d 15N ) were reported. 300 The experimental 13 C NMR chemical shift components of uracil in the solid state were reported for the first time (to our knowledge), as well as newer data for the 15 N nuclei.…”

The 15N induced isotope shift as an effective tool for the structure elucidation of 2,4 and 2,5 di-substituted thiazoles

“…In this context, 15 N-isotopic labeling offers a wider range of NMR approaches to be exploited for the determination of molecular structures 6 and of reaction mechanisms in solution. In particular, the successful use of 15 N labeling in the structural investigation of indazoles is well documented.…”