Published papers

© 2018 Office of the Federal Register. All rights reserved. Microwave irradiation is widely applied to organic synthesis. Many advantages of microwave irradiation, including drastic shortening of reaction time, suppression of side reactions, and/or higher chemical yield, have been proposed. Generally, these effects have been understood merely as a simple thermal effect, since microwave irradiation rapidly raises the temperature of the reaction mixture. However, some observed results could not be understood only by the thermal effect. Recently our group reported that several enantioselective reactions were accelerated under microwave irradiation without loss of enantioselectivity. As these extraordinary results could not be explained by the simple thermal effect, the concept of the "microwave-specific effect" should be considered. We describe our recent experimental results to elucidate the microwave-specific effect. Investigations are described on enantioselective ring-opening reactions of biaryl lactone derivatives, racemization of an optically pure biaryl lactone derivative, enantioselective Claisen rearrangement reaction, enantioselective Conia-ene reaction and ring-closing metathesis reaction. These reactions or racemization of optically pure compounds were accelerated under microwave conditions. Such reaction acceleration of enantioselective reactions was observed without loss of enantioselectivity.

© 2018 The Chemical Society of Japan. The amidation reaction of carboxylic acid derivatives was developed using sulfur trioxide pyridine complex (SO3•py) as a commercially available and easily handled oxidant. This method could be applied to the reaction of various aromatic and aliphatic carboxylic acids, including optically active ones, with formamide derivatives to afford the corresponding amides in good to high yields.

© 2020 The Chemical Society of Japan. Decarboxylative Nazarov cyclization of chiral cyclic enol carbonates proceeded to afford chiral 2-cyclopentenones with excellent chirality transfer under thermal conditions without any catalyst. Interestingly, the thermal decarboxylative Nazarov cyclization furnished the desired product with better chirality transfer than the Lewis acid-catalyzed reaction.

A copper-catalyzed Nazarov cyclization was carried out under conventional heating conditions and microwave conditions. Under strictly temperature-controlled conditions, the use of microwave irradiation improved the chemical yields. Consequently, the kinetic rate of the microwave irradiation was 5.8 times higher than that of the conventional heating conditions. These observations suggested that the microwave specific effects enhanced the efficiency of the Nazarov reaction.

A Lewis acid-catalyzed decarboxylative substitution reaction of cyclic enol carbonates with a cyanation reagent was developed to give ¢-ketonitriles in good yield. It is proposed that the reaction proceeds through an oxyallyl cation intermediate or its equivalent. Interestingly, cyanation selectively took place at the more hindered site of the intermediate to afford a multi-substituted ¢-ketonitrile. This regioselectivity was observed by the cyanation of a wide range of substrates and is discussed in terms of the reaction mechanism.

© 2018 IEICE The microwave specific effect was investigated on the catalytic enantioselective reactions; atropo-enantiveselective ring-opening reaction of biaryl lactones and enantioselective Claisen rearrangement reaction. These reactions were efficiently enhanced with microwave irradiation under reaction temperature control, thought any loss of the enantioselectivities were not detected. It was also found that the racemization rate of the atropo-optically active biaryl lactone was enhanced by microwave irradiation. As these observations could not be explained by the simple thermal effect, microwave specific effect should be considered.

© 2019 American Chemical Society. Asymmetric synthesis of 2-cyclopentenones was achieved by chirality transfer based on Lewis acid catalyzed decarboxylative Nazarov cyclization of optically active cyclic enol carbonates, which are prepared by silver-catalyzed carbon dioxide incorporation into optically pure propargyl alcohols. The stereochemistry at the 4,5-positions of the 2-cyclopentenones was cleanly constructed by reflecting the stereochemistry of the starting materials. This method could be applied to various substrates to obtain the corresponding products in high yields with highly efficient chirality transfer.

© 2019 The Royal Society of Chemistry. The combined use of an organic base for resorcinols realized a Kolbe-Schmitt type reaction under ambient conditions. When resorcinols (3-hydroxyphenol derivatives) were treated with DBU under a carbon dioxide atmosphere, nucleophilic addition to carbon dioxide proceeded to afford the corresponding salicylic acid derivatives in high yields.

© The synthesis of polycyclic indene derivatives via silver-catalyzed carbon dioxide fixation on 2-alkynylindene derivatives was achieved by nucleophilic addition of the indenyl anion to carbon dioxide involving carbon-carbon bond formation and subsequent intramolecular cyclization to the alkyne part activated by a silver catalyst. This cascade process could be applied to various substrates to obtain the corresponding products in high yields. The endo/exo selectivity of the cyclization could be controlled by the steric or electronic effect of the substituents on the substrates, and 6-endo-selective cyclization was realized to afford α-pyrone-fused indenes.

© The Royal Society of Chemistry. The stereoselective synthesis of aminovinyloxazolidinones based on the electrophilic amination of a vinyl-silver intermediate, generated by silver-catalyzed carbon dioxide incorporation on a propargyl amine, was achieved. The geometry of the aminated product was determined by a single crystal X-ray analysis and NOE measurement and it was elucidated that the geometry was proved to be opposite to the geometry predicted from the previous silver-catalyzed carbon dioxide fixation on a propargyl amine derivative. This unexpected stereoselectivity could be successfully explained by a radical mechanism. This journal is