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.

Optical switching of self-assembly and disassembly of noncovalently connected amphiphiles.

A hydrophobic compound, which we name 3C18-Azo, containing an azo head and three 18 C alkyl chains has the capacity to form an amphiphile by capping it with a cyclodextrin (CD) by inclusion complexation. The amphiphilic compound self-assembles into vesicles in water. Optical switching of the assembly and disassembly is realized by alternating visible and UV irradiation, which causes the isomerization of the azo groups, thus affecting their complexation with the CDs.

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.

A new photochromic tetrahydroindolizine.

The title compound, dimethyl 10b'-(4-fluorostyryl)-8',9'-dimethoxy-4-nitro-5',6'-dihydrospiro[9H-fluorene-9,1'(10b'H)-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.

Microwave-assisted synthesis of diaryl ethers without catalyst.

[reaction: see text] Diaryl ethers have been prepared by direct coupling of phenols including those that bear a strong electron-attracting substituent to electron-deficient aryl halides through S(N)Ar-based addition reactions with assistance of microwave irradiation in high to excellent yields within 5-10 min. No catalysts were required under our conditions.

On the 6-exo atom transfer radical cyclization reactions of 3-butenyl 2-iodoalkanoates.

Bis(tributyltin)-initiated atom transfer cyclization reactions of 3-butenyl iodoalkanoates in the presence of BF3.OEt2 as the catalyst afforded the 6-exo cyclization products as a mixture of 3,4-cis- and trans-substituted tetrahydro-2H-pyran-2-ones in 53-71% yield with the major isomers being the cis ones. Ab initio calculations at the B3LYP/6-31G level on the transition states of the radical cyclization and on the cyclized products revealed that the reactions are kinetically controlled and the transition states for the 6-exo radical cyclization are in boat conformations. Moreover, the cis-oriented transition states are of lower energy than the corresponding trans-oriented ones, which are in excellent agreement with experimental results.

K(2)CO(3)-catalyzed Michael addition-lactonization reaction of 1,2-allenyl ketones with electron-withdrawing group substituted acetates. An efficient synthesis of alpha-pyrone derivatives.

[reaction: see text] Alpha-pyrone derivatives were synthesized via the base catalyzed or promoted reaction of 1,2-allenyl ketones and electron-withdrawing group substituted acetates. The reaction was believed to proceed through a Michael addition C-C double-bond migration-lactonization process.