Pyrimidin‐/thiazol‐/thiazolin‐ylidenamidothiophosphoric dichlorides

Nine new amidodichlorothiophosphorus(V) derivatives incorporating pyrimidine, thiazole, and thiazoline rings were obtained by sulfurization of the corresponding aminodichlorophosphines generated in situ from the reaction of the respective N‐alkyl‐2‐aminocycloiminium halide with PCl₃ in the presence of triethylamine. These pyrimidin‐/thiazol‐/thiazolin‐ylidenamidothiophosphoric dichlorides were isolated as stable crystalline solids and are well characterized by elemental analysis, NMR, and mass spectroscopy. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:498–502, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10170     

Boric acid: a novel and safe catalyst for aza-Michael reactions in water

Boric acid efficiently catalyzes the conjugate addition of aliphatic amines to α,β-unsaturated compounds to produce β-amino compounds, with great alacrity and excellent yields, in water under mild conditions. Aromatic amines do not participate effectively in the reaction.     

Synthetic applications of 2-chloro-3-formylquinoline

New examples of synthetic applications of 2-chloro-3-formylquinoline, as evident from the novel and facile syntheses of 3-aminoisooxazolo[5,4-b]quinoline (4), 3-hydroxyfuro[2,3-d]theino[2,3-b]quinoline-2-carboxamide (7) and 3-hydroxymethyl-2-(3-formyl)phenylquinoline ( 13 ), have been furnished.     

A binuclear manganese complex of a pyridoxal derivative and its use as an oxidation catalyst

Summary A new binuclear complex of manganese, [Mn₂L(OAc)₂], where H₃L = N,N-[4(3-hydroxy-5-hydroxymethyl-2-methyl)pyridylmethylene]-1,3-diamionopropane-2-ol, was prepared and characterized by analysis and various spectral methods. The studies reveal that it is a mixed valence manganese(II)/manganese(III) complex with endogenous -oxo and exogenous -carboxylato bridges.The complex can be used as a catalyst for the selective oxidation of hydrocarbons (cyclohexene, cis-cyclooctene, styrene, norbornene and trans-4-octene) using terminal oxidant at ambient temperatures. The yields calculated on the basis of the oxidant concentrations indicate that the complex works as an efficient catalyst for the oxidation of hydrocarbons. A probable mechanism for the reaction is proposed.     

Theoretical investigation of an unusual substituent effect on the dienophilicity of >CP? functionality present in 2‐phosphaindolizines

Effect of the number and positions of the methoxycarbonyl substituents in 2‐phosphaindolizine on the feasibility of its Diels–Alder (DA) reaction with 1,3‐butadiene has been investigated theoretically at the density functional theory (DFT) level. Among the series of four differently substituted 2‐phosphaindolizines, 3‐methoxycarbonyl‐2‐phosphaindolizine does not undergo the DA reaction due to the highest activation barrier (29.49 kcal mol^?1) and endothermicity, whereas the activation barrier of the corresponding reaction of 1,3‐bis(methoxycarbonyl)‐2‐phosphaindolizine is lowest (22.43 kcal mol^?1) with exothermicity making it possible to occur. This reactivity trend is corroborated by FMO energy gaps as well as by global electrophilicity powers of the reactants. Copyright © 2008 John Wiley & Sons, Ltd.     

Diels–Alder reactions of 5,6‐dihydrothiazolo[3,2‐d][1,4,2]diazaphospholes: A DFT investigation

The density functional theory level (B3LYP/6‐311G**) computations of the Diels–Alder (DA) reactions of 5,6‐dihydrothiazolo[3,2‐d][1,4,2]‐diazaphospholes with 1,3‐butadiene and with isoprene confirm pericyclic mechanism via asynchronous transition states. The aromatic character of the transition states is established by negative nucleus independent chemical shift (NICS) values falling in the range from −14 to −16. Integration of the dienophilic >CP functionality in the 6π aromatic azaphosphole ring raises the activation energy barrier (B3LYP/6‐311++G**//B3LYP/6‐311G**) compared to that for the DA reaction of the acyclic phosphaethene, but it is lower than the activation energy barrier for the DA reaction of the corresponding 10π aromatic system, thiazolo[3,2‐d][1,4,2]diazaphospholes. The experimentally observed stereo‐ and regioselectivities in the reactions can be accounted on the basis of secondary molecular orbital (SMO) interactions detected in the respective transition structures. The attachment of an electron‐withdrawing group to the dienophilic moiety enhances both stereo‐ and regio‐ selectivities which agree well with the experimental values. Solvent (toluene) effect studied with polarizable continuum model (PCM) indicates that the stereo‐ and regioselectivities are not affected by the solvent. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:402–410, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20196     

‘One-pot’ organocatalyzed enantioselective synthesis of highly functionalized 3,4,5,6-tetrasubstituted dihydropyrans by sequential Knoevenagel condensation/Michael addition and hemiacetalization

An organocatalytic ‘one-pot’ synthesis of highly functionalized 3,4,5,6-tetrasubstituted dihydropyrans has been developed. Excellent enantio- and diastereo selectivity with good yields are some of the salient features of this methodology. This reaction takes advantage of proline based catalysts and follows stepwise sequential transformations including Knoevenagel condensation–Michael addition–hemiacetalization towards the synthesis of complex dihydropyranol framework.     

1,5‐electrocyclization versus 1,5‐proton shift in imidazolium allylides and 2‐phospha‐allylides: a DFT investigation

The competitive 1,5‐electrocyclization versus intramolecular 1,5‐proton shift in imidazolium allylides and imidazolium 2‐phosphaallylides has been investigated theoretically at the DFT (B3LYP/6‐311 + +G**//B3LYP/6‐31G**) level. 1,5‐Electrocyclization follows pericyclic mechanism and its activation barrier is lower than that for the pseudopericyclic mechanism by ～5–6 kcal mol^?1. The activation barriers for 1,5‐electrocyclization of imidazolium 2‐phosphaallylides are found to be smaller than those for their nonphosphorus analogues by ～3–5 kcal mol^?1. There appears to be a good correlation between the activation barrier for intramolecular 1,5‐proton shift and the density of the negative charge at C8, except for the ylides having fluorine substituent at this position ( 7b and 8b ). The presence of fluorine atom reduces the density of the negative charge at C8 (in 7b it becomes positively charged) and thus raises the activation barrier. The ylides 7f and 8f having CF₃ group at C8, in preference to the 1,5‐proton shift, follow an alternative route leading to different carbenes which is accompanied by the loss of HF. The carbenes Pr _{7 , 8b – e} resulting from intramolecular 1,5‐proton shift have a strong tendency to undergo intramolecular S_N2 type reaction, the activation barrier being 7–28 kcal mol^?1. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis and characterization of polyaniline: nanospheres,nanorods, and nanotubes—catalytic application for sulfoxidation reactions

The synthesis of nanostructured polyaniline (PANI) with different morphologies by simple alkali‐guided template‐free method followed by doping them with vanadium has been described. The synthesized polyaniline nanoparticles have been well characterized by various techniques. Further, the catalytic activity of the undoped and doped PANI nanostructures for selective oxidation of sulfides to sulfoxides in water has been studied. It was observed that the special morphology of nanostructures plays an important role in enhancement of catalytic activity. Vanadium‐doped PANI nanotubes and nanorods showed higher activity and selectivity than nanospheres. The catalyst has been reused for five consecutive cycles with consistent activity. Copyright © 2008 John Wiley & Sons, Ltd.