Desymmetrization of 1,4-pentadien-3-ol by the asymmetric 1,3-dipolar cycloaddition of azomethine imines.

Desymmetrization of the divinyl carbinol 1,4-pentadien-3-ol was accomplished by the asymmetric 1,3-dipolar cycloaddition of azomethine imines based on a magnesium-mediated, multinucleating chiral reaction system utilizing diisopropyl (R,R)-tartrate as the chiral auxiliary. The corresponding optically active trans-pyrazolidines, each with three contiguous stereogenic centers, were obtained with excellent regio-, diastereo-, and enantioselectivity, with results as high as 99% ee. This reaction was shown to be applicable to both aryl- and alkyl-substituted azomethine imines. The use of a catalytic amount of diisopropyl (R,R)-tartrate was also effective when accompanied by the addition of MgBr2.

A three-component reaction of C,N-cyclic N'-acyl azomethine imines, isocyanides, and azide compounds: effective synthesis of 1,5-disubstituted tetrazoles with tetrahydroisoquinoline skeletons.

A multicomponent reaction of isocyanides and C,N-cyclic N'-acyl azomethine imines in the presence of TMSCl and NaN3 leads to tetrazole derivatives. These reactions proceeded cleanly to afford the corresponding 1,5-disubstituted tetrazoles containing a tetrahydroisoquinoline skeleton in high to excellent yields.

1-Acetyl-5-(4-fluoro-phen-yl)-2-sulfanyl-ideneimidazolidin-4-one.

In the title compound, C11H9FN2O2S, the 2-sulfanylideneimidazolidin-4-one moiety is essentially planar, with a maximum deviation of 0.0183 (14) Å. The mean plane of this moiety is approximately coplanar with the attached acetyl group and perpendicular to the benzene ring, making dihedral angles of 9.70 (14) and 86.70 (6)°, respectively. In the crystal, mol-ecules are linked by N-H⋯O hydrogen bonds between the amide NH and acetyl C=O groups, forming a C(6) chain along the a-axis direction.

5-Isopropyl-5-methyl-2-sulfanylidene-imidazolidin-4-one.

In the title compound, C7H12N2OS, the 2-sulfanylideneimidazolidin-4-one moiety is nearly planar, with a maximum deviation of 0.054 (2) Å. In the crystal, a pair of N-H⋯O hydrogen bonds and a pair of N-H⋯S hydrogen bonds each form a centrosymmetric ring with an R 2 (2)(8) graph-set motif. The enanti-omeric R and S mol-ecules are alternately linked into a tape along [1-10] via these pairs of hydrogen bonds.

Chlorosilane-promoted addition reaction of isocyanides to 3,4-dihydroisoquinoline N-oxides.

The addition reaction of isocyanides to 3,4-dihydroisoquinoline N-oxides in the presence of TMSCl has been demonstrated, with the corresponding 1,2,3,4-tetrahydroisoquinoline-1-carboxylamides being obtained in moderate to high yields. A wide range of 3,4-dihydroisoquinoline N-oxides and isocyanides were applicable to this reaction.

Clickable di- and tetrafunctionalized pillar[n]arenes (n = 5, 6) by oxidation-reduction of pillar[n]arene units.

We report a new route for the selective synthesis of di- and tetrafunctionalized pillararenes via oxidation and reduction of the pillararene units. Hypervalent-iodine oxidation of perethylated pillar[5]arene afforded pillar[5]arene derivatives containing one benzoquinone unit and two benzoquinones at the A,B- and A,C-units. A pillar[6]arene derivative containing one benzoquinone unit was also synthesized. Reduction of the benzoquinone units yielded position-selective di- and tetrahydroxylated pillararene derivatives. This methodology avoids the generation of many constitutional isomers and overcomes the isolation problem of numerous constitutional isomers. From these hydroxylated pillararenes, Huisgen reaction-based clickable di- and tetraalkynylated pillar[5]arenes were prepared. Because of the highly selective and reactive nature of Huisgen alkyne-azide cycloaddition, these pillar[5]arenes can serve as key compounds for a large library of di- and tetrafunctionalized pillararenes. Based on these di- and tetrafunctionalized pillar[5]arenes as key compounds, fluorescent sensors were created by the modification of di- and tetrapyrene moieties via Huisgen-type click reactions.

Facile, rapid, and high-yield synthesis of pillar[5]arene from commercially available reagents and its X-ray crystal structure.

We monitored the progress of formation of dimethoxypillar[5]arene by size-exclusion chromatography. Surprisingly, the cyclization reaction completely finished in just 3 min. By improving the reaction conditions and purification process, we successfully obtained dimethoxypillar[5]arene in a short time and in high yield (71%) from commercially available reagents. By improving the deprotection reaction of the methoxy moieties, pillar[5]arene was isolated quantitatively. Single crystal X-ray analysis confirmed the structure of pillar[5]arene in the solid state.

Synthesis and conformational characteristics of alkyl-substituted pillar[5]arenes.

A series of pillar[5]arene derivatives with alkyl groups of different length were synthesized. The new alkyl-substituted pillar[5]arene derivatives 1,4-bis(ethoxy)pillar[5]arene (C2), 1,4-bis(propoxy)pillar[5]arene (C3), 1,4-bis(butoxy)pillar[5]arene (C4), 1,4-bis(pentyloxy)pillar[5]arene (C5), 1,4-bis(hexyloxy)pillar[5]arene (C6), and 1,4-bis(dodecanoxy)pillar[5]arene (C12) were obtained by Lewis acid-catalyzed condensation of dialkoxybenzene monomers with paraformaldehyde. The conformational characteristics of the pillar[5]arene derivatives were investigated by dynamic (1)H NMR measurements. When the alkyl substituents were bulkier than methyl groups, the rotation of phenolic units in the pillar[5]arenes was suppressed and their conformation was immobilized. As their length increased, the alkyl substituents packed at the upper and lower rims and thus lowered the conformational freedom of the pillar[5]arenes.

Aliphatic C-H bond activation initiated by a (mu-eta2:eta2-peroxo)dicopper(II) complex in comparison with cumylperoxyl radical.

A (mu-eta(2):eta(2)-peroxo)dicopper(II) complex, [Cu(2)(H-L)(O(2))](2+) (1-O(2)), supported by the dinucleating ligand 1,3-bis[bis(6-methyl-2-pyridylmethyl)aminomethyl]benzene (H-L) is capable of initiating C-H bond activation of a variety of external aliphatic substrates (SH(n)): 10-methyl-9,10-dihydroacridine (AcrH(2)), 1,4-cyclohexadiene (1,4-CHD), 9,10-dihydroanthracene (9,10-DHA), fluorene, tetralin, toluene, and tetrahydrofuran (THF), which have C-H bond dissociation energies (BDEs) ranging from approximately 75 kcal mol(-1) for 1,4-CHD to approximately 92 kcal mol(-1) for THF. Oxidation of SH(n) afforded a variety of oxidation products, such as dehydrogenation products (SH((n-2))), hydroxylated and further-oxidized products (SH((n-1))OH and SH((n-2))=O), dimers formed by coupling between substrates (H((n-1))S-SH((n-1))) and between substrate and H-L (H-L-SH((n-1))). Kinetic studies of the oxidation of the substrates initiated by 1-O(2) in acetone at -70 degrees C revealed that there is a linear correlation between the logarithms of the rate constants for oxidation of the C-H bonds of the substrates and their BDEs, except for THF. The combination of this correlation and the relatively large deuterium kinetic isotope effects (KIEs), k(2)(H)/k(2)(D) (13 for 9,10-DHA, approximately > 29 for toluene, and approximately 34 for THF at -70 degrees C and approximately 9 for AcrH(2) at -94 degrees C) indicates that H-atom transfer (HAT) from SH(n) (SD(n)) is the rate-determining step. Kinetic studies of the oxidation of SH(n) by cumylperoxyl radical showed a correlation similar to that observed for 1-O(2), indicating that the reactivity of 1-O(2) is similar to that of cumylperoxyl radical. Thus, 1-O(2) is capable of initiating a wide range of oxidation reactions, including oxidation of aliphatic C-H bonds having BDEs from approximately 75 to approximately 92 kcal mol(-1), hydroxylation of the m-xylyl linker of H-L, and epoxidation of styrene (Matsumoto, T.; et al. J. Am. Chem. Soc. 2006, 128, 3874).

Oxidation reactivity of bis(mu-oxo) dinickel(III) complexes: arene hydroxylation of the supporting ligand.

In the nick(el) of time: Bis(mu-oxo) dinickel(III) complexes 2 (see scheme), generated in the reaction of 1 with H(2)O(2), are capable of hydroxylating the xylyl linker of the supporting ligand to give 3. Kinetic studies reveal that hydroxylation proceeds by electrophilic aromatic substitution. The lower reactivity than the corresponding mu-eta(2):eta(2)-peroxo dicopper(II) complexes can be attributed to unfavorable entropy effects.

para-Bridged symmetrical pillar[5]arenes: their Lewis acid catalyzed synthesis and host-guest property.

Condensation of 1,4-dimethoxybenzene (DMB) with paraformaldehyde in the presence of BF3.O(C2H5)2 gave novel para-bridged pentacyclic pillar DMB (DMpillar[5]arene). Moreover, para-bridged pentacyclic hydroquinone (pillar[5]arene) was prepared. Pillar[5]arene formed 1:1 host-guest complexes with dialkyl viologen and alkyl pyridinium derivatives. However, pillar[5]arene did not form complexes with the diadamantyl viologen derivative since a bulky adamantyl group was unable to thread the cavity of pillar[5]arene.

New mechanistic insights into intramolecular aromatic ligand hydroxylation and benzyl alcohol oxidation initiated by the well-defined (µ-peroxo)diiron(iii) complex.

A (µ-peroxo)diiron(iii) complex [Fe2(LPh4)(O2)(Ph3CCO2)]2+ (1-O2) with a dinucleating ligand (LPh4), generated from the reaction of a carboxylate bridged diiron(ii) complex [Fe2(LPh4)(Ph3CCO2)]2+ (1) with dioxygen in CH2Cl2, provides a diiron(iv)-oxo species as an active oxidant which is involved in either aromatic ligand hydroxylation or benzyl alcohol oxidation.

New mechanistic insight into intramolecular arene hydroxylation initiated by (µ-1,2-peroxo)diiron(III) complexes with dinucleating ligands.

(µ-1,2-Peroxo)diiron(iii) complexes (-R) with dinucleating ligands (R-L) generated from the reaction of bis(µ-hydroxo)diiron(ii) complexes [Fe2(R-L)(OH)2](2+) (-R) with dioxygen in acetone at -20 °C provide a diiron-centred electrophilic oxidant, presumably diiron(iv)-oxo species, which is involved in aromatic ligand hydroxylation.

Regioselective hydroxylation of the xylyl linker in a diiron(III) complex having a carboxylate-rich ligand with H2O2.

Reaction of a diiron(III) complex having a xylta4- ligand (N,N,N',N'-m-xylylenediamine tetraacetate) with H2O2 resulted in regioselective hydroxylation of the m-xylyl linker. The reaction mimics the self-hydroxylation of a phenylalanine side chain found for ribonucleotide reductase (R2-W48F/D84E).

Ring enlargement reaction of C,N-cyclic-N'-acyl azomethine imines with sulfonium ylide: an efficient synthesis of 3-benzazepine derivatives.

Highly efficient formation of 3-benzazepine derivatives has been achieved, based on the ring expansion reaction of C,N-cyclic-N'-acyl azomethine imines with sulfonium ylide generated in situ from the corresponding sulfonium salt. The reactions proceeded smoothly to afford the tricyclic 3-benzazepine derivatives in good to high yields. A wide range of C,N-cyclic N'-acyl azomethine imines were applicable to this reaction.

N-heterocyclic carbene catalyzed oxidative coupling of aldehydes with carbodiimides under aerobic conditions: efficient synthesis of N-acylureas.

The oxidative coupling reaction of aldehydes with N,N'-disubstituted carbodiimides catalyzed by N-heterocyclic carbenes under aerobic conditions has been achieved. This reaction gives the corresponding N-acylurea derivatives in good to high yields. Various kinds of aldehydes including aliphatic ones and carbodiimides are applicable to this reaction.

Magnesium-tartramide complex mediated asymmetric Strecker-type reaction of nitrones using cyanohydrin.

An asymmetric Strecker-type reaction of nitrones using acetone cyanohydrin as a source of HCN has been realized. A magnesium-tartramide complex, generated from (R,R)-2,3-dihydroxy-1,4-di(pyrrolidin-1-yl)-butane-1,4-dione and MeMgBr, promoted transcyanation from the bromomagnesium salt of the cyanohydrin, in the presence of a catalytic amount of DBU, to afford the corresponding optically active (S)-α-amino nitrile derivatives. The reaction was applicable to various nitrones giving high-to-excellent enantioselectivities.

One-pot stereoselective synthesis of 2-acylaziridines and 2-acylpyrrolidines from N-(propargylic)hydroxylamines.

The stereoselective direct transformation of N-(propargylic)hydroxylamines into cis-2-acylaziridines was achieved by the combined use of AgBF4 and CuCl. Copper salts were found to promote the transformation of the intermediary 4-isoxazolines into 2-acylaziridines and both 3-aryl- and 3-alkyl-substituted 2-acylaziridines could be prepared by using this method. Furthermore, subsequent 1,3-dipolar cycloaddition of azomethine ylides that were generated in situ from the intermediary 2-acylaziridines with maleimides was achieved in a stereoselective one-pot procedure to afford the corresponding 2-acylpyrrolidines, which consisted of an octahydropyrrolo[3,4-c]pyrrole skeleton.

Synthesis and X-ray crystal structure of a difunctionalized pillar[5]arene at A1/B2 positions by in situ cyclization and deprotection.

The reaction of 1,4-dimethoxybenzene and paraformaldehyde using AlBr(3) yields multiple-deprotected pillar[5]arenes. A1/B2 di-deprotected pillar[5]arene can be isolated by silica gel chromatography and washing procedures. The X-ray structure and polymerization of the A1/B2 di-deprotected pillar[5]arene are reported.