Fenggang Tao

A facial synthesis of the neutral [1,2,4]triazolo-[3,2-d][1,5]benzoxazepines and their chalcogen-analogues

ABSTRACT An expedient synthesis of neutral [1,2,4]triazolo[3,2-d][1,5]-benzoxazepines 6a–e and their chalcogen analogues 6f–i was accomplished via cycloaddition of the heterocumulene cations (3a,b), generated sequentially by action of chroman-4-one as well as thiochroman-4-one ethoxy carbonylhydrazones (1a,b) with t-BuOCl and SbCl5, to the triple bond of nitriles and concurring ring enlargement and hydrolytic removal of the N(1)-ethoxycarbonyl group. The oily final products were characterized as their picrates.

Synthesis of 2‐Oxo‐[1,2,4]triazolo[3,2‐d][1,5]benzoxazepines: A Kind of Novel Tricyclic O,N‐Heterocycles

Abstract The synthesis of a series of novel tricyclic O,N‐heterocycles 7a–k, a kind of unprecedented 2‐oxo‐[1,2,4]triazolo[3,2‐d][1,5]benzoxazepine derivatives, has been accomplished, featuring acid‐induced ring closure of the geminal arylazo isocyanato compounds 5, which were prepared from chroman‐4‐ones in three steps, followed by feasible ring expansion and basic work‐up.

ALLYLATION OF ESTERS PROMOTED BY METALLIC DYSPROSIUM IN THE PRESENCE OF MERCURIC CHLORIDE

ABSTRACT In the presence of mercuric chloride, the reactions of esters with allyl bromide and metallic dysprosium in anhydrous THF give diallyl alkyl carbinols in good yields. When γ-butyrolactone is used as the substrate, the corresponding product is 4-allyl-6-heptene-1, 4-diol.

A Convenient Method for Synthesis of Gem-bromochlorocyclopropanes

Abstract Gem-bramochlorocyclopropanes can be prepared by a convenient method based on the reaction of the mixtures of haloforms and tetrahalomethanes or hexahaloethane with powdered sodium hydroxide.

A DFT study on dissociation of diborane (B2H6) in dimethyl sulfide media

Abstract The detailed dissociation mechanism of diborane (B 2 H 6 ) in dimethyl sulfide (Me 2 S) media has been studied at the levels of B3LYP/6-311G**//B3LYP/6-31G* and B3PW91/6-311G**//B3PW91/6-31G*. All the calculations predict a two-step mechanism for the dissociation and only one H-bridge bond is broken in each. In comparison with the dissociation of B 2 H 6 in vacuum or in hydrocarbon media, the participation of Me 2 S significantly lowers the activation barriers in the process. The barriers are even more lowered when solvent effect is embraced.

A DFT study on the mechanisms for the cycloaddition reactions between 1−aza-2-azoniaallene cations and acetylenes

The mechanisms of cycloaddition reactions between 1-aza-2-azoniaallene cations 1 and acetylenes 2 have been investigated using the global electrophilicity and nucleophilicity of the corresponding reactants as global reactivity indexes defined within the conceptual density functional theory. The reactivity and regioselectivity of these reactions were predicted by analysis of the energies, geometries, and electronic nature of the transition state structures. The theoretical results revealed that the reaction features a tandem process: an ionic 1,3-dipolar cycloaddition to produce the cycloadducts 3 H-pyrazolium salts 3 followed by a [1,2]-shift affording the thermodynamically more stable adducts 4 or 5. The mechanism of the cycloaddition reactions can be described as an asynchronous concerted pathway with reverse electron demand. The model reaction has also been investigated at the QCISD/6-31++G(d,p) and CCSD(T)/6-31++G(d,p)//B3LYP/6-31++G(d,p) levels as well as by the DFT. The polarizable continuum model, at the B3LYP/6-31++G(d,p) level of theory, was used to study solvent effects on all the studied reactions. In solvent dichloromethane, all the initial cycloadducts 3 were obtained via direct ionic process as the result of the solvent effect. The consecutive [1,2]-shift reaction, in which intermediates 3 are rearranged to the five-membered heterocycles 4/5, is proved to be a kinetically controlled reaction, and the regioselectivity can be modulated by varying the migrant. The LOL function and RDG function based on localized electron analysis were used to analysis the covalent bond and noncovalent interactions in order to unravel the mechanism of the title reactions.

SYNTHESIS OF HYDROXYCEDRANONE AND AMINOHYDROXYCEDRANE

Abstract Two optically pure derivatives of α-cedrene — (1R,2R,5S,7R,8R)- 8-hydroxy-9-cedranone 2 and (lR,2R,5S,7R,8R,9S)-9-amino-8-hydroxycedrane 4 were prepared conveniently. An X-ray structural analysis of 2 was performed indicating that the hydroxycedranone exists as dimer due to one hydrogen bond in solid state.

ASYMMETRIC HOMOLOGATION OF CEDRANEDIOL BORONIC ESTERS AND X-RAY STRUCTURE OF CEDRANEDIOL 1-CHLORO-1-PHENYLMETYLBORONATE

Abstract Homologation of cedranediol boronic esters 1, RBO,C15H,4l with (dichloromethyl)lithium resulted in the formation of (αR)-α-chloro boronic esters 3, RCHCIBO2C15H24, consistently yielding (R)/(S)ratios over 25:1. The absolute configuration of cedranediol (R)-1-chloro-1-phenylmethylboronate 3dR was determined by X-ray diffraction. The distortion of the five-membered 1,3,2-dioxaborolane ring of 3dR from planarity was found. The reason why the cedranediol boronic esters are prone to hydrolysis has been discussed.

PREPARATION OF CEDRANEDIOL BORONIC ESTERS

Abstract (-)-Cedranediol boronic esters 4, a series of asymmetric homologation reagents were prepared from a new chiral director (-)-cedranediol 3 and boronic acids. (-)-Cedranediol 3 was easily synthesized by the dihydroxylation of (-)-α-cedrene 2 with OsO4. A more convenient method for the preparation of boronic acids was developed as well.

Di­methyl 2-(4-bromo­phenyl)-10,11-di­methoxy-2,3,7,8-tetra­hydro­spiro­[azepino[2,1-a]­iso­quinoline-3,9′-fluorene]-4,5-di­carboxyl­ate

The title compound, C38H32BrNO6, is a new photochromic tetrahydroazepinoisoquinoline (THAI). The longest spiro bond [1.589 (4) A] can be broken very easily by UV light, leading to ring opening. This explains the photochromic behaviour.