Selective Formation of 5- or 6-Membered Rings, 1,3-Thiazolidin-4-one vs. 1,3-Thiazin-4-one, from Acridine Thiosemicarbazides by the Use of Ethyne Acid Esters

4-(9,10-Dihydroacridin-9-ylidene)thiosemicarbazide and its five-membered thiazole and six-membered thiazine derivatives

“…The geometric parameters for the acridine moiety in (I), (II) and (III) correspond to aromatic portions (outer rings), whilst the central C9 0 -C9a 0 and C8a 0 -C9 0 bonds pertain very much to typical C-C single bonds and overall the parameters are similar to previous reports (Klika et al, 2001;Imrich et al, 2005;Č erná k et al, 1995). The placement of a labile H atom on N10 0 confirms the NMR assignments (Imrich et al, 2010). Although the acridine moieties are not aromatic over the entire segment, they are, nevertheless, almost planar in all structures; the largest deviations of C9 0 from the mean planes of the 14 non-H atoms of the acridine moieties are 0.184 (3) and 0.180 (3) Å for (I) and (II), respectively.…”

“…For unequivocal gross structural confirmation, in particular the size of the newly formed rings, as well as to elucidate the fine structural elements, crystals of three derivatives, viz. fivemembered methyl 2-{2-[2-(9,10-dihydroacridin-9-ylidene)-1-methylhydrazinyl]-4-oxo-4,5-dihydro-1,3-thiazol-5-ylidene}acetate, (I), six-membered 2-[2-(9,10-dihydroacridin-9-ylidene)-1-methylhydrazino]-4H-1,3-thiazin-4-one, (II), and unsubstituted 4-(9,10-dihydroacridin-9-ylidene)thiosemicarbazide, (III), were obtained (Imrich et al, 2010) and subjected to X-ray single-crystal analysis. Of more than 70 crystallographic descriptions of structures containing an acridine moiety and several hundred descriptions of structures containing thiazolidine rings (Allen, 2002), only four reports exist which contain both acridine and thiazolidine entities linked in some manner (Klika et al, 2001;Imrich et al, 2005;Č erná k et al, 1995).…”

Synthesis, Characterization and Molecular Docking of Novel Bioactive Thiazolyl-Thiazole Derivatives as Promising Cytotoxic Antitumor Drug

“…Thus, the 1 H-NMR spectrum showed singlet signal at δ 12.77 ppm (D2O-exchangeable), assignable to NH group. In addition, the presence of a signal at δ 6.60 assigned to the =CH, and singlet at δ 3.29 for ester methyl protons [9,[26][27][28]. Next, the reaction of 1-[1-(2-amino-4-methylthiazol-5-yl)ethylidene]thiosemicarbazide 3b with α-keto-hydrazonoyl halides 4a-f was performed under similar reaction conditions, and afforded the final product 5-hydrazono-thiazole derivatives 14a-f via same route of elimination HCl and H 2 O (Scheme 4) [25].…”

“…Thus, the 1 H-NMR spectrum showed singlet signal at δ 12.77 ppm (D 2 O-exchangeable), assignable to NH group. In addition, the presence of a signal at δ 6.60 assigned to the =CH, and singlet at δ 3.29 for ester methyl protons [9,[26][27][28]. …”

Differentiation between 6- and 7-Membered Rings Based on Theoretical Calculation of NMR Parameters

“…In addition to solving this somewhat persistent problem as an example of the wider application of DFT-calculated NMR parameters such as δ H , δ C , and J H,H for differentiating Figure 1: Depiction of various NMR parameters considered in a previous study [1] for rendering distinction between 5-and 6-membered ring products, namely, 1,3-thiazolidin-4-one and 1,3-thiazin-4-one products, respectively, obtained [10,11] from 2-substituted 1-(9-acridinyl) thiosemicarbazides by reagent selection (dimethyl acetylenedicarboxylate in the former case and methyl propiolate in the latter case). The structures of the 6-membered ring product 3,4-dihydro-2H-3-hydroxymethyl-1,4-benzoxazine (1) and the isomeric 7-membered ring product 2,3,4,5-tetrahydro-1,5-benzoxazepine-3-ol (2).…”