Aarti Dalal

Synthesis of some benzothiazoles by developing a new protocol using urea nitrate as a catalyst and their antimicrobial activities

ABSTRACT The present communication demonstrates the development of urea nitrate as an effective and efficient catalyst for the synthesis of some 2-substituted benzothiazoles. Instant progress of reaction at room temperature under solvent-free condition, very high catalytic activity, inexpensive, clean reaction profile, operational simplicity, large-scale synthesis and appreciable yields are the main advantages of this protocol. These synthesized benzothiazoles have been evaluated for their antibacterial and antifungal activities against Gram-positive bacterium (Bacillus subtilis MTCC 121); two Gram-negative bacteria (Escherichia coli MTCC 1652 and Pseudomonas aeruginosa MTCC 741) and two fungi (Candida albicans MTCC 3017 and Saccharomyces cerevisiae MTCC 170). Compound 3n was found the most active against all the tested microbes. GRAPHICAL ABSTRACT

Crystal structure of (Z)-3-[5-chloro-2-(prop-2-yn­yloxy)phen­yl]-3-hy­droxy-1-[4-(tri­fluoro­meth­yl)phen­yl]­prop-2-en-1-one

The title compound, C19H12ClF3O3, obtained by the photochemical transformation of 2-[5-chloro-2-(prop-2-ynyloxy)benzoyl]-3-[4-(trifluoromethyl)phenyl]oxirane adopts a Z conformation with respect to the enolic C=C double bond. The dihedral angle between the benzene rings is 12.25 (16)° and an intramolecular O—H⋯O hydrogen bond closes an S(6) ring. An intramolecular C—H⋯O interaction also leads to an S(6) ring. In the crystal, very weak C—H⋯O interactions and short Cl⋯Cl contacts [3.3221 (16) Å] are seen, as well as weak aromatic π–π stacking interactions [centroid–centroid separation = 3.879 (2) Å].

Photochemical Transformation of some 3-benzyloxy-2-(benzo[b]thiophen-2-yl)-4Hchromen-4-ones: A Remote Substituent Effect

Abstract The effect on photochemical transformations of the substituents present remotely from the reaction site in 3-benzyloxy-2-(benzo[b]thiophen-2-yl)-4H-chromen-4-ones has been determined. The structure(s) of the substrates and photoproducts were established by spectroscopic techniques (UV, IR, and NMR). The substituents had profound effects on product yield and distribution. Electron withdrawing groups (EWGs) on the benzenoid moiety of the chromenone nucleus increased the yield of the photoproducts whereas electron donating groups (EDGs) decreased the yield. These results may be attributed to “state switching” of the substituents during excitation. Graphical Abstract

Absorption and Fluorescent Studies of 3-Hydroxychromones

The synthesis and spectral studies of variously substituted 3-hydroxychromones have been carried out. A key relationship between the structural motif of synthesized 3-hydroxychromones (3-HCs) and their fluorescent properties was found. The chromones substituted with electron-donating group at 4′-position expressed the red shift of the N* and T* band and also exhibited the increased fluorescent intensity ratio while the chromones with electron-withdrawing group showed the blue shift of the N* and T* band. Therefore, these 3-HCs may behave as the possible fluorescent probes.