NHC-catalysed diastereoselective synthesis of multifunctionalised piperidines via cascade reaction of enals with azalactones

NHC-catalysed azalactone ring-opening and piperidine ring-closing cascade with α,β-unsaturated aldehydes (enals) in a one-pot operation is reported. The present reaction cascade offers a convenient method for a highly diastereoselective synthesis of multifunctionalised piperidines in excellent yields under mild conditions.     

Arsenic(III) sorption on nanostructured cerium incorporated manganese oxide (NCMO): a physical insight into the mechanistic pathway

Arsenic(III) sorption was investigated with nanostructured cerium incorporated manganese oxide (NCMO). The pH between 6.0 and 8.0 was optimized for the arsenic(III) sorption. Kinetics and equilibrium data (pH=7.0±0.2, T=303±1.6 K, and I=0.01 M) of arsenic(III) sorption by NCMO described, respectively, the pseudo-second order and the Freundlich isotherm equations well. The sorption process was somewhat complicated in nature and divided into two different segments, initially very fast sorption followed by slow intraparticle diffusion process. Sorption reaction of arsenic(III) on NCMO was endothermic (ΔH°=+13.46 kJ mol(-1)) and spontaneous (ΔG°=-24.75 to -30.15 kJ mol(-1) at T=283-323 K), which took place with increasing entropy (ΔS°=+0.14 kJ mol(-1)K(-1)) at solid-liquid interface. Energy of arsenic(III) sorption estimated by analyzing the equilibrium data using the D-R isotherm model was 15.4 kJ mol(-1), indicating the ion-exchange type mechanism. Raman, FT-IR, pH effect, desorption, etc. studies indicated that arsenic(III) was oxidized to arsenic(V) during the sorption process.     

Visible-light-promoted aerobic oxidative cyclization to access 1,3,4-oxadiazoles from aldehydes and acylhydrazides

A novel and practical access to symmetrical and unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles directly from aldehydes and acylhydrazides using visible light irradiation under an air atmosphere in the presence of eosin Y as an organophotoredox catalyst at rt is reported. This is the first example of oxidative cyclization of acylhydrazones employing air and visible light as inexpensive, readily available, non-toxic, and sustainable reagents.     

An organocatalytic synthesis of N-sulfonyl imines using chloramine-T in aqueous medium

N-Sulfonyl imines have been synthesized in good to excellent yields from aldehydes and chloramine-T using proline as an organocatalyst in aqueous medium at ambient temperature. The protocol is applicable to a wide range of aldehydes, especially enals exhibit remarkable efficiency in the reaction. The reaction presumably occurs via iminium activation and opens new avenues for the synthesis of N-sulfonyl imines under environmentally benign and mild conditions.     

Photosensitizer in a molecular bowl and its effect on the DNA-binding and -cleavage activity of 3d-metal scorpionates

Ternary 3d -metal complexes [M(Tp (Ph))(B)](ClO 4) ( 1- 8), where M is Co(II), Ni(II), Cu(II) and Zn(II), Tp (Ph) is anionic tris(3-phenylpyrazolyl)borate, and B is N,N-donor heterocyclic base, namely, 1,10-phenanthroline (phen, 1- 4) and dipyrido[3,2- d:2',3'- f]quinoxaline (dpq, 5- 8), were prepared from a reaction of the perchlorate salt of the metal with KTp (Ph) and B in CH 2Cl 2. The complexes were characterized by various physicochemical methods. 4- 6 and 8 were structurally characterized by single-crystal X-ray crystallography. The crystal structures of the complexes show the presence of discrete cationic complexes having a square-pyramidal (4 + 1) coordination geometry in which two nitrogen atoms of the phenanthroline base (B) and two nitrogen atoms of the Tp (Ph) ligand occupy the basal plane and one nitrogen of the Tp (Ph) ligand binds at the axial site. The phenyl groups of the Tp (Ph) form a bowl-shaped structure that essentially encloses the {M(phen/dpq)} moiety. DNA-binding studies were carried out using various spectral techniques and from viscosity measurements. The complexes show moderate binding propensity to calf thymus DNA at the minor groove, giving binding constant values ( K b) of approximately 10 (4) M (-1). The complexes exhibit poor DNA-cleavage activity in the dark in the presence of 3-mercaptopropionic acid (MPA) or hydrogen peroxide (H 2O 2). The photoinduced DNA-cleavage activity of the complexes was investigated using UV-A radiation of 365 nm and visible light of two different wavelengths with a tunable multicolor Ar-Kr mixed gas ion laser source. The dpq complexes show efficient photoinduced DNA-cleavage activity via a metal-assisted photoexcitation process involving the formation of singlet oxygen as the cleavage active species in a type-II pathway. The paramagnetic d (7)-Co(II)-dpq and d (9)-Cu(II)-dpq complexes exhibit efficient DNA-cleavage activity in visible light. The paramagnetic d (8)-Ni(II)-dpq complex displays only minor DNA-cleavage activity in visible light. Diamagnetic d (10)-Zn(II)-dpq complex shows only UV-A light-induced DNA cleavage but no apparent DNA-cleavage activity in visible light. Steric protection of the photoactive quinoxaline moiety of the dpq ligand inside the hydrophobic {M(Tp (Ph))} molecular bowl has a positive effect on the photoinduced DNA-cleavage activity.     

Synthesis and characterization of {Ni(NO)}10 and {Co(NO)2}10 complexes supported by thiolate ligands

Nitric oxide is an important molecule in biology and modulates a variety of physiological and pathophysiological processes. Some of its regulatory functions are exerted through interactions with redox-active elements, including iron, nickel, cobalt, and sulfur. Metalloenzymes containing [ nFe- nS] ( n = 2 or 4) clusters can be activated or inactivated by reaction with NO, affording dinitrosyl iron complexes. Studies of the NO chemistry of small-molecule iron thiolate complexes have provided insight into these biological processes and suggested probable intermediates. To explore this chemistry from a different perspective, we prepared nickel and cobalt thiolate complexes and investigated their reactions with NO and related compounds. We report here the first examples of anionic complexes containing {Ni(NO)} (10) and {Co(NO) 2} (10) units, the reactivity of which suggests possible intermediates in the interconversion of iron thiolate nitrosyl compounds. Our results demonstrate new chemistry involving NO and simple complexes of nickel and cobalt supported by thiolates, which have been known for more than 30 years. The use of mass balance methodology was key to their discovery. Among the novel complexes reported are (Et 4N) 2[Ni(NO)(SPh) 3] ( 2), from (Et 4N) 2[Ni(SPh) 4] ( 1) and NO, (Et 4N) 2[Ni 2(NO) 2(mu-SPh) 2(SPh) 2] ( 3), from 1 and NO (+) or 2 and Me 3O (+), (Et 4N)[Co(NO) 2(SPh) 2] ( 5), from (Et 4N) 2[Co(SPh) 4] ( 4) and NO, and [Co 3(NO) 6(mu-SPh) 3] ( 6), from 5 and Me 3O (+). In the syntheses of 2 and 5, NO could be replaced by the convenient solid Ph 3CSNO.     

Chiral ionic liquid-catalyzed Biginelli reaction: stereoselective synthesis of polyfunctionalized perhydropyrimidines

A chiral ionic liquid-catalyzed, efficient and unprecedented version of the Biginelli reaction using new variants of its active methylene component, viz. 2-phenyl-1,3-oxazol-5-one/2-methyl-2-phenyl-1,3-oxathiolan-5-one, with aromatic aldehydes and urea/thiourea enantio- and diastereoselectively, yields 5-amino-/mercaptoperhydropyrimidines. This three-component domino cyclocondensation reaction is effected via ring transformation of an isolable intermediate in a one-pot procedure.     

Ionic liquid [Hmim]HSO4-promoted one-pot oxidative conjugate addition of sulfur-centred nucleophiles to Baylis-Hillman adducts

The first example of the one-pot oxidative conjugate addition of sulfur-centred nucleophiles to Baylis-Hillman adducts is reported. The reaction involves oxidation of Baylis-Hillman adducts with NaNO₃ in the Brønsted acidic ionic liquid [Hmim]HSO₄ to give [E]-α-cyanocinnamaldehydes followed by conjugate hydrothiocyanation/hydrosulfenylation with NH₄SCN/PhSH to afford the corresponding β-thiocyanato (or β-phenylsulfenyl)-α-cyanohydrocinnamaldehydes diastereoselectively in 76-89% yields in a one-pot procedure. After isolation of the product, the ionic liquid [Hmim]HSO₄ could be easily recycled for further use.     

Thiourea to bicyclic scaffolds: highly regio- and stereoselective routes to dithiazolopyrimidines

Microwave-activated solvent-free Michael addition of 3-imino-1,4,2-dithiazoles to 4-arylidene-5(4H)-oxazolones furnished isolable adducts regio- and diastereoselectively, which underwent ring transformation to yield the target dithiazolopyrimidines. Alternatively, the similar conjugate addition of methanesulfinylmethylisothioureas to 4-arylidene-5(4H)-oxazolones diastereoselectively afforded Michael adducts, which underwent ring transformation followed by heterocyclization via deoxygenative demethylation with thionyl chloride to yield the same products dithiazolopyrimidines regio- and diastereoselectively.