Crystal structure, Hirshfeld surface analysis and computational study of a rhodamine B–salicylaldehyde Schiff base derivative

The molecular structure of the title compound {systematic name: 3′,6′-bis(diethylamino)-2-[(2-hydroxybenzylidene)amino]spiro[isoindoline-1,9′-xanthen]-3-one}, C35H36N4O3 or RbSa, can be seen as being composed of two parts sharing a central quaternary carbon atom. Both the xanthene and isoindole moieties are nearly planar: 14 atoms in the former moiety show an r.m.s. deviation of 0.0411 Å and eleven atoms in the latter moiety show an r.m.s. deviation of 0.0545 Å. These two planes are almost perpendicular to each other, the angle between the mean planes being 87.71 (2)°. The title compound appears to be in its enol form. The corresponding H atom was located and freely refined at a distance of 1.02 (3) Å from the O atom and 1.72 (2) Å from the N atom. The strong intramolecular hydrogen bond O—H...N bridging the hydroxyl group and its neighboring nitrogen atom forms an S(6) graph-set motif. Apart from the intramolecular O—H...N hydrogen bond, C—H...O interactions are observed between two neighbouring RbSa molecules related by an inversion center. The C—O donor–acceptor distance is 3.474 (2) Å. Moreover, C—H...π interactions are observed between the C—H bond of one of the ethyl groups and the centroid of the benzene ring of the isoindole moiety. The C...centroid distance is 3.8191 (15) Å. No π–π interactions are observed in the crystal structure as the shortest distance between ring centroids is more than 4 Å. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H...H, C...H/H...C, O...H/H...O and N...H/H...N interactions. DFT calculations at the CAM-B3LYP/6–31 G(d) level were carried out to gain a better understanding of the relative energies and the tautomerization process between two possible conformers (keto and enol), as well as the transition state of the title compound.

Three-component reaction between isatoic anhydride, amine and methyl-substituted furylacrylaldehydes: crystal structures of 3-benzyl-2-[(E)-2-(5-methylfuran-2-yl)vinyl]-2,3-dihydroquinazolin-4(1H)-one, 3-benzyl-2-[(E)-2-(furan-2-yl)-1-methylvinyl]-2,3-dihydroquinazolin-4(1H)-one and 3-(furan-2-ylmethyl)-2-[(E)-2-(furan-2-yl)-1-methylvinyl]-2,3-dihydroquinazolin-4(1H)-one

Compounds (I), C22H20N2O2, (II), C22H20N2O2 and (III), C20H18N2O3 are the products of three-component reactions between isatoic anhydride, the corresponding amine and 3-(5-methylfuran-2-yl)- or (furan-2-yl)-2-methylacrylaldehyde. Compound (I) crystallizes in the monoclinic space group P21/n, while compounds (II) and (III) are isostructural and crystallize in the orthorhombic space group Pbca. The tetrahydropyrimidine ring in (I)–(III) adopts a sofa conformation. The NH nitrogen atom has a trigonal–pyramidal geometry, whereas the N(R) nitrogen atom is flattened. The furyl-vinyl substituents in (I)–(III) are practically planar and have an E configuration at the C=C double bond. In (I), this bulky fragment occupies the axial position at the quaternary carbon atom of the tetrahydropyrimidine ring, whereas in (II) and (III) it is equatorially disposed. In the crystal of (I), molecules form hydrogen-bonded chains propagating along [001] by strong intermolecular N—H...O hydrogen bonds. The chains are packed in stacks along the a-axis direction. In the crystals of (II) and (III), molecules also form hydrogen-bonded chains propagating along [100] by strong intermolecular N—H...O hydrogen bonds. However, despite the fact that compounds (II) and (III) are isostructural, steric differences between the phenyl and furyl substituents result in chains with different geometries. Thus in the crystal of (II) the chains have a zigzag-like structure, whereas in the crystal of (III), they are almost linear. In both (II) and (III), the hydrogen-bonded chains are further packed in stacks along the b-axis direction.

Synthesis of ribavirin 2’-Me-C-nucleoside analogues

An efficient synthetic pathway leading to two carbonated analogues of ribavirin is described. The key-steps in the synthesis of these ribosyltriazoles bearing a quaternary carbon atom in the 2’-position are an indium-mediated alkynylation and a 1,3-dipolar cyclization.