Zhiming Li

IBD-mediated oxidative cyclization of pyrimidinylhydrazones and concurrent Dimroth rearrangement: Synthesis of [1,2,4]triazolo[1,5-c]pyrimidine derivatives.

Summary Oxidative cyclization of 6-chloro-4-pyrimidinylhydrazones 4 with iodobenzene diacetate (IBD) in dichloromethane gives rise to [1,2,4]triazolo[4,3-c]pyrimidine derivatives 5a–o. These incipient products undergo feasible Dimroth rearrangement to furnish the isolated [1,2,4]triazolo[1,5-c]pyrimidines 6a–o in moderate to high yields.

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 3u2009H-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.

A SYNTHESIS OF β-ALLYL SUBSTITUTED ISOTETRONIC ACID DERIVATIVES VIA THERMAL CLAISEN REARRANGEMENT

Isotetronic acids are of great interest in agricultural and pharmacological research and occur in a number of natural products. This paper describes the first Claisen rearrangement of the O-allyl substituted isotetronic acids 2 under thermal conditions furnishing the β-allyl substituted isotetronic acid derivatives 3 in high yields.

A new photochromic tetrahydroindolizine.

The title compound, dimethyl 10b-(4-fluorostyryl)-8,9-dimethoxy-4-nitro-5,6-dihydrospiro[9H-fluorene-9,1(10bH)-pyrrolo[2,1-a]isoquinoline]-2,3-dicarboxylate, C38H31FN2O8, is a new photochromic tetrahydroindolizine. One of the C-C bonds at the spiro C atom is very long [1.630 (2) A], thus explaining the photochromic behaviour.

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.