Unsymmetrization of 1,8-Dibromonaphthalenes by Acid-Induced Halogen Dance Reaction.

A simple and powerful tool for preparing uncommon bromoarenes via the unsymmetrization of a naphthalene ring was developed. The steric repulsion between the peri-bromo groups of 1,8-dibromonaphthalene distorts the naphthalene ring, allowing for nonelectronical activation. Ring distortion facilitates the 1,2-rearrangement of the bromo group, affording 1,7-dibromonaphthalene upon treatment with trifluoromethanesulfonic acid (halogen dance reaction). For 1,4,5,8-tetrabromonaphthalene, stepwise 1,2-rearrangements proceeded successively to furnish 1,3,5,7-tetrabromonaphthalene. Density functional theory calculations suggest that this reaction is initiated by ipso-protonation, with a subsequent 1,2-rearrangement occurring via the bromonium transition state. Utilizing 1,7-dibromonaphthalene, which is characterized by two C-Br bonds arranged at a 60° angle, a unique metal-organic framework comprising a 52-membered ring network was synthesized.

Highly electron-deficient 1-propyl-3,5-dinitropyridinium: evaluation of electron-accepting ability and application as an oxidative quencher for metal complexes.

Impacts of the nitro groups on the electron-accepting and oxidizing abilities of N-propylpyridinium were evaluated quantitatively. A 3,5-dinitro derivative has efficiently quenched emission from photosensitizing Ru(ii) and Ir(iii) complexes owing to the thermodynamically-favored electron transfer to the pyridinium whose LUMO is greatly lowered by the presence of electron-withdrawing nitro groups.

Cationic Iridium-Catalyzed Decarboxylation of Aromatic Carboxylic Acids.

Practical synthetic applications of catalytic decarboxylation in producing useful molecules are limited. We report herein the cationic Ir-catalyzed decarboxylations of various electron-rich and -poor aromatic carboxylic acids to produce hydrocarbons in good yield (up to >99%). Additionally, this reaction is applicable in decarboxylative hydroarylation of bicyclic alkenes and decarboxylative fluorination, indicating the potential utility of this catalytic decarboxylation in synthetic chemistry.

A Study of the Correlation between the Bulkiness of peri-Substituents and the Distortion of a Naphthalene Ring.

A systematic study on the distortion of a naphthalene ring was performed using steric repulsion between peri-substituents at the 1- and 8-positions. The introduction of bromo groups into the methyl groups of the 1,8-dimethylnaphthalene enhanced the steric repulsion to distort the naphthalene ring. X-ray crystallography revealed that 1,8-bis(bromomethyl)naphthalene had a vertical distortion with a 11.0° dihedral angle (α) between peri-substituents which disturbed the coplanarity of the naphthalene ring. On the other hand, the dihedral angle of 1,8-bis(dibromomethyl)naphthalene was smaller (α = 8.3°) despite the bulkier substituents. In this case, horizontal distortion of the naphthalene ring increased. These distortions should non-electronically activate the naphthalene framework. In order to evaluate their reactivity, nitration and hydrogenation were carried out; however, the 1,8-bis(dibromomethyl)naphthalene was intact under the employed conditions. A DFT calculation suggested that the inertness of the 1,8-bis(dibromomethyl)naphthalene is presumably due to the negative hyperconjugation of the (dibromo)methyl group.

First synthesis of acylated nitrocyclopropanes.

Although nitrocyclopropanedicarboxylic acid esters are widely used in organic syntheses, nitrocyclopropanes with an acyl group have not yet been synthesized. When adducts of ß-nitrostyrene and 1,3-dicarbonyl compounds are treated with (diacetoxyiodo)benzene and tetrabutylammonium iodide, iodination occurs at the α-position of the nitro group, and the subsequent O-attack of the enol moiety leads to 2,3-dihydrofuran. Cyclopropane was successfully synthesized through C-attack as the acyl group became bulkier. The obtained nitrocyclopropane was transformed into furan upon treatment with tin(II) chloride via a ring-opening/ring-closure process.

Halo-Jacobsen Rearrangement Induced by Steric Repulsion between peri-Iodo Groups.

The naphthalene ring is distorted due to steric repulsion between iodo groups at the peri-positions. Due to the distortion, 1,8-diiodonaphthalene underwent a halo-Jacobsen rearrangement when treated with trifluoromethanesulfonic acid, producing 1,5-diiodonaphthalene and 1,4-diiodonaphthalene. In this reaction, acid-induced dehalogenative homocoupling also proceeded to form 4,4'-diiodo-1,1'-binaphthyl. The reaction selectivity could be controlled by varying the reaction temperature. DFT calculations and some control experiments revealed that these compounds were formed by different pathways.

Synthesis of Bis(functionalized) Aminals via Successive Nucleophilic Amidation and Amination.

The central carbonyl group of diethyl mesoxalate (DEMO) exhibits high electrophilicity that allows it to be attacked by versatile nucleophiles. Even a less nucleophilic acid amide serves as a nucleophile to produce N,O-acetal upon treatment with DEMO in the presence of acetic anhydride. When the obtained N,O-acetal was treated with a base, the elimination of acetic acid generated N-acylimine in situ. N-Acylimine is also highly electrophilic, allowing it to accept the second nucleophilic addition by an amine, resulting in α,α-bis(functionalized) aminals. This protocol facilitates the modification of the two different amino groups by altering nucleophiles, resulting in the production of tetra-functionalized methane derivatives on demand. The ring closure between the amide moiety and the amino group was achieved using the structural features to form a six-membered ring.

Unusual Reactivities of ortho-Hydroxy-ß-nitrostyrene.

Nitrostyrene derivatives are widely used in organic syntheses as a substrate for Michael addition, photoisomerization and cycloaddition. In contrast, ortho-hydroxy derivatives exhibit unusual behaviors in these reactions. Conjugate addition proceeded upon treatment of the ortho-hydroxy-ß-nitrostyrene with an amine; however, subsequent C-C bond cleavage readily occurred to afford the corresponding imine. Moreover, conversion of the trans-isomer to a cis-isomer did not occur efficiently, even when UV light was irradiated. We studied these unusual behaviors of ß-nitrostyrene, focusing on the role of the ortho-hydroxy group.

A new approach to 10-arylated 5H-dibenzo[b,f]azepines using syn-selective hydrohalogenation of ethynylaniline.

A new synthetic method for 10-arylated dibenzo[b,f]azepines was developed. The pseudo-intramolecular hydrohalogenation of 2-(2'-bromophenyl)ethynylaniline, which proceeded in a syn-selective manner without forming any detectable over-addition product, was a crucial step. All attempts of subsequent arylation via Suzuki-Miyaura cross coupling and construction of a seven membered ring via Ullmann-type intramolecular coupling were unsuccessful because of dehydrohalogenation or other side reactions. This problem was overcome by the N-acetylation of the amino group, which facilitated the abovementioned coupling reactions to afford the desired 10-arylated dibenzoazepines.

Utilization of phosphonic acid compounds by marine bacteria of the genera Phaeobacter, Ruegeria, and Thalassospira (α-Proteobacteria).

Phosphonic acid (phosphonate) that possesses a carbon-phosphours bond is a chemically stable form of organic phosphorus. Various phosphonic acids are widely distributed in oceanic waters; in particular, methylphosphonic acid (namely methylphosphonate) is believed to be responsible for global methane production. To discuss the microbial degradation of phosphonic acids, we investigated the utilization of phosphonic acid compounds by cultures of marine bacteria, Phaeobacter sp., Ruegeria sp. (Rhodobacterales), and Thalassospira sp. (Rhodospirillales). These bacterial cultures were able to grow on methylphosphonic acid as well as on the tested alkyl-, carboxy-, aminoalkyl-, and hydroxyalkyl-phosphonic acid compounds. Cell yields and growth rates of Ruegeria and Thalassospira cultures grown on methyl-, ethyl-, propyl-, and butyl-phosphonic acid compounds tended to decrease with increasing alkyl chain length. In contrast, Phaeobacter sp. grew well on such alkyl-phosphonic acids. Our results suggest that these marine bacteria, which exhibit varied utilization, are involved in microbial degradation of various phosphonic acid compounds.