Structural tuning of ß-enamino diketones: exploration of solution and crystalline state photochromism.

A library of ß-enamino diketones was prepared via base-mediated, three-component reaction of 4-hydroxycoumarins with various aromatic/aliphatic amines and ß-nitrostyrenes under microwave irradiation conditions to investigate their photochemical properties. Among the prepared compounds, a thiophene derived ß-enamino diketone was found to be light-sensitive and to exhibit unique photochromic behavior, that is, positive photochromism in solution and negative photochromism in crystalline phase. In addition, this prepared photochromic compound was further covalently linked to a structure-related, piezochromic ß-enamino diketone moiety to explore its potential multi-stimuli responsive properties.

4-Chloro-3-nitrocoumarin as a precursor for synthesis of 2-arylchromeno[3,4-b]pyrrol-4(3H)-ones: a case of nitro group directed reductive coupling.

A series of 2-aryl substituted chromeno[3,4-b]pyrrol-4(3H)-ones were prepared in two steps by employing 4-chloro-3-nitrocoumarin as a precursor. The reaction involved the base-mediated reductive coupling of 4-chloro-3-nitrocoumarin with α-bromoacetophenone, followed by reductive intramolecular cyclization to afford the pyrrolocoumarin ring. When α-bromoacetophenone was replaced with α-cyanoacetophenone, (E)-4-(nitromethylene)-4H-chromen-2-amine was isolated as the major product. The molecular structures of the prepared compounds were characterized by X-ray crystallography and the mechanisms for their formation were proposed.

(2-Hy-droxy-phen-yl)(4,2':4',4''-terpyridin-6'-yl)methanone.

The title compound, C22H15N3O2, can be described as a ketone with a phenol substituent and a terpyridine ligand coordinated to the carbonyl group. The three six-membered rings of the terpyridine ligand are not coplanar. The dihedral angles between the mean planes of the central ring and the external pyridine ligands are 22.77 (9) and 26.77 (7)°. The central ring of the terpyridine ligand is also not coplanar with the o-hy-droxy phenyl ring, the dihedral angle being 39.72 (5)°. An intra-molecular O-H⋯O hydrogen bond occurs. The crystal structure of the title compound is consolidated by C-H⋯O and C-H⋯N hydrogen bonding inter-actions.

New design of highly sensitive AIE based fluorescent imidazole derivatives: Probing of sweat pores and anti-counterfeiting applications.

A novel aggregation induced emission based 2-(1-(3, 5-bis(trifluoromethyl)phenyl)-4,5-diphenyl-1H-imidazol-2-yl) phenol (4) (IMD) fluorescent tags (FTs) was designed by simple acid catalyzed five-member N-heterocyclic ring forming reaction process. Powder X-ray diffraction results showed mechanofluorochromic properties of IMD FTs are easily reversible under external force due to the decrease in crystallinity. These IMD FTs also exhibits strong cyan-blue luminescence in solid state with high quantum efficiency. Detailed investigation of latent fingerprints (LFPs) showed permanent, immutable and unique pores that are distributed on the ridges. The visualization of such sweat pores opens new avenue in the field of forensic science. Hence, the prepared IMD FTs exhibit excellent Lipophicity (LP) properties, which endorse its possible applications for the visualization of sweat pores present in the LFPs. The LFPs visualized by IMD FTs exhibit excellent efficiency, sensitivity, selectivity, low background hindrance and less toxicity. The obtained result evident that the prepared FT and followed technique opens possible applications for the visualization of LFPs on various porous/semi-porous/non-porous surfaces under UV 365 nm light.

Structural tuning enables piezochromic and photochemical properties in N-aryl-ß-enaminones.

An efficient synthesis of N-aryl-ß-enaminones via Et3N-mediated, one-pot three-component reaction of 4-hydroxycoumarin/dimedone, ß-nitrostyrene/2-(2-nitrovinyl)thiophene, and arylamine in toluene under refluxed conditions is herein presented. Some prepared compounds were found to exhibit piezochromic properties. The XRD and SEM measurements of the piezochromic compound showed substantial crystal packing and morphology changes before and after grinding. Further, one prepared compound was found to be light-sensitive and can be converted to a furo[3,2-b]pyridin-2(4H)-one derivative upon UV irradiation. A plausible mechanism for this photochemical reaction was proposed.

Visible-Light-Promoted and Yb(OTf)3-Catalyzed Constructions of Coumarin-Pyrrole-(Iso)quinoline-Fused Pentacycles: Synthesis of Lamellarin Core, Lamellarin D Trimethyl Ether, and Lamellarin H.

The efficient construction of a coumarin-pyrrole-isoquinoline-fused pentacycle via the visible-light-promoted cyclization of 4-(isoquinolin-1-ylmethyl)-3-nitrocoumarin or Yb(OTf)3-catalyzed coupling of 4-chloro-3-nitrocoumarin and 1-methylisoquinoline is reported. This methodology has further led to the development of the concise synthesis of the lamellarin core in one, two, and three steps, as well as of lamellarin D trimethyl ether in three steps.

Microwave-promoted, metal- and catalyst-free decarboxylative α,ß-difunctionlization of secondary α-amino acids via pseudo-four-component reactions.

A microwave-promoted, metal- and catalyst-free decarboxylative α,ß-difunctionlization of secondary α-amino acids via a pseudo-four-component coupling of proline, aldehyde, and 1,3-diketone to generate multifunctionalized pyrano[2,3-b]pyrrole and pyrrolizinone derivatives is reported.