Molecular and solid-state structure of methyl [2-(acridin-9-ylimino)-3-(tert-butylamino)-4-oxothiazolidin-5-ylidene]acetate

The molecular and solid-state structures of methyl [2-(acridin-9-ylimino)-3-(tert-butylamino)-4-oxothiazolidin-5-ylidene]acetate (4) were determined by X-ray diffraction, 1H NMR, 13C NMR, CI mass spectroscopy and B3LYP calculations using the basis sets 6-31G(d, p), 6-311+G(d, p) and 6-311++G(2d, 2p). In particular, calculations of long-range heteronuclear coupling constants were found to be extraordinarily indicative for the E/Z configuration of a distal segment. Compound 4 (C23H22N4O3S, Mr = 434.52) crystallized in the P1¯ space group wherein: a = 11.973(4), b = 12.398(3), c = 15.289(4) Å and α = 85.80(2)°, β = 73.70(3)°, γ = 87.93(2)°, V = 2172.2(11) Å3, Z = 4 and calculated density = 1.329 g cm−3. The formation of dimers, chains and the crystal packing between the molecules by means of intermolecular hydrogen bonds and π-π interactions between neighboring acridine moieties are discussed. NMR spectral analysis and quantum chemical calculations were found to be in good agreement with the results of the X-ray study. The observation of 4 indicates the dominate role that the N-2 nitrogen of the isothiosemicarbazide intermediate plays in its formation via the reaction of 4-(acridin-9-yl)-1-(tert-butyl)thiosemicarbazide with dimethyl acetylenedicarboxylate (DMAD). This dominance is a result of the steric influences of the substituents on the competing nitrogen atoms.