Hirofumi Maekawa

Selective and one-pot formation of phenols by anodic oxidation☆

Abstract Direct monohydroxylation of benzene and substituted benzenes was successfully performed by anodic oxidation to form the corresponding phenol derivatives in good yields. The anodic oxidation was generally carried out in a mixed solvent of trifluoroacetic acid and dichloromethane containing triethylamine using a divided cell equipped with a platinum plate as the anode, a carbon rod as the cathode. Benzene derivatives having electron withdrawing groups were suitable for the present electrochemical oxidation. It was clarified that aryltrifluoroacetates were formed as the initial products from the reaction of the radical cations, generated by one electron transfer from the substrates, with trifluoroacetic acid, followed by hydrolysis during work-up to give the corresponding phenols.

Diacylation of activated olefins promoted by electrochemically generated NO3·p1☆

Abstract It has been found in this study that an acyl radical is formed by the reaction of an aldehyde with a radical NO3· generated by the anodic oxidation of NO3− and the reaction of this acyl radical with activated olefins lead to the formation of a diacylated compound.

Highly selective and facile synthesis of dihydro- and tetrahydropyridine dicarboxylic acid derivatives using electroreduction as a key step

Abstract Electroreduction of pyridinedicarboxylic acid derivatives 1a – g in methanol containing ammonium chloride using a divided cell brought about highly selective hydrogenation to give the corresponding dihydropyridines in good yields. From the electrolysis of dimethyl 2,3- and 2,5-pyridinedicarboxylates 1a , c , only the corresponding 1,2-dihydropyridine derivatives 2a , c were obtained in a regioselective manner while that of 2,4-, 2,6-, and 3,4- disubstituted pyridines 1b , d , e afforded the corresponding 1,4-dihydropyridines 2b , d , e selectively in good yields. Further hydrogenation of the resultant dihydropyridines by several methods led to the selective and facile formation of the corresponding tetrahydropyridines 6 . Furthermore, Mg-promoted hydrosilylation of the N-acetylated product 5a gave C-silylated tetrahydropyridines in a stereoselective manner.

Facile synthesis of silyl enol ethers by Mg-promoted coupling of aliphatic carbonyl compounds with trimethylsilyl chloride

Abstract Treatment of aliphatic carbonyl compounds with trimethylsilyl chloride with Mg turning for Grignard reaction without any pre-treatment in N,N-dimethylformamide at room temperature brought about highly facile, effective and stereoselective coupling to give the corresponding silyl enol ethers in good yields.

Mg-promoted carbon-acylation of aromatic aldehydes and ketones

Reductive cross-coupling of aromatic aldehydes and ketones with aliphatic acid chlorides promoted by Mg turnings in DMF at room temperature brought about efficient C-acylation to afford the corresponding α-acyloxy-α-aryl ketones in good yields. Treatment of α-methoxy or α-acetoxyacetophenones under similar conditions gave the corresponding α-acyloxystyrenes exclusively. The reaction may be initiated by electron transfer from Mg to the carbonyl groups of the substrates.

Selective and facile electroreductive synthesis of dihydro- and tetrahydropyridine dicarboxylic acid derivatives

Abstract Electroreduction of pyridinedicarboxylic acid derivatives in methanol using a divided cell brought about highly selective hydrogenation to give efficiently the corresponding dihydropyridines in good yields. From the electrolysis of dimethyl 2,3- and 2,5-pyridinedicarboxylates, 1,2-dihydropyridine derivatives were obtained while that of 2,6-, 3,4- and 2,4-disubstituted pyridines afforded the corresponding 1,4-dihydropyridines selectively in good yields.

Synthesis and behavior of novel phthalocyanines possessing intramolecular crown ether bridges between their different aromatic rings for effective extraction multi metal inclusion

Abstract Novel Cu- and Co-phthalocyanines (7a–e, 8a, b) possessing intramolecular crown ether bridges between their different aromatic rings were successfully synthesized from the reaction of the corresponding bisphthalonitriles (6a–e) bearing polyethyleneoxy chains in the presence of CuCl and CoCl2, respectively. As 1,8-diazabicyclo [5.4.0]-7-undecene (DBU) was used as a base in n-pentanol at reflux temperature for 30 h under N2 atmosphere, these new phthalocyanines were found to be characteristic of satisfactory solubility in some of organic solvents, and showed strong absorption bands in ultraviolet and visible wave length region (λmaxZ719–739 nm). Extraction experiment of metal chlorides (NaCl, KCl, MgCl2, CaCl2, CeCl3, ZnCl2, FeCl3) in chloroform was carried out by using Cu-phthalocyanine (7b) bearing two intramolecular bridges with tri(ethyleneoxy) chains. Among these metal salts, 7b formed a complex (9b) with only FeCl3, which showed a dark-red amorphous solid. Spectroscopic analysis of the complex (9b) indicated that original strong absorption bands near 738 nm characteristic for phthalocyanines completely disappeared, and new two strong bands appeared near 799–853 nm. FAB-MASS spectrum of the complex (9b) showed that new strong peaks came out in the region centered at m/z Z1879 and 1881 besides original peaks in the region centered at 1488, which corresponded to molecular peak of the starting phthalocyanine (7b). These facts indicated that the complex (9b) included two molecules of FeCl3 into the protonated crown ether bridges of the phthalocyanine skeleton. Furthermore, it was found that the complex (9b) was transformed to the original phthalocyanine (7b) quantitatively by treatment with triethylamine.

Intramolecular electroreductive cyclization of heteroatom-containing non-conjugated enones and ynones

Electroreduction of non-conjugated enones and ynones containing a sulfur or a nitrogen atom in the connecting chains brought about regio- and stereoselective intramolecular cyclization to give the corresponding heteroatom-containing cyclic alcohols in moderate to good yields. These materials may be useful synthetic intermediates of biologically active compounds. Some decrease in stereoselectivity on intramolecular cyclization of nitrogen-containing non-conjugated enones is rationalized by postulating that the lone pair electrons of the nitrogen atom repel the negative charges on the oxygen atoms and the alkyl carbon atoms of the cyclized anion radical intermediates.

Regioselective synthesis of substituted tropones and azulenes using anodic oxidation of cycloheptatriene systems as the key reaction

Abstract Regioselective synthesis of di- and trisubstituted tropones has been attained by utilizing anodic oxidation of cyclohepatatriene systems as the key reaction. This anodic oxidation has also been found to be useful for the regioselective synthesis of mono- and disubstituted azulenes.

Unusual Rearrangement by Anodic Oxidation of Cycloalkanones in the Presence of Trifluoroacetic Acid

Anodic oxidation of cyclopentanone and cyclohexanones in a mixed solvent of CF3COOH and CH2C12 containing triethylamine led to unusual rearrangement to give selectively γ-valerolactone and a mixture of γ-and δ-lactones, respectively.