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A skeletal transformation of α-pyrones having electron-withdrawing groups at the 3,5-positions into dihydrofurans was developed. Using dimethylsulfoxonium methylide as the methylene-transfer reagent, the α-pyrones were converted into dihydrofurans as major products and 1-methylthiopyran-1-oxides as minor products. The selectivity of the dihydrofuran formation was improved by optimizing the reaction conditions.

Pyrrolophenanthridinone derivatives including the natural products were readily synthesized by samarium(II)-mediated reductive cyclization of aryl radical onto a benzene ring under mild reaction conditions. This methodology was applied to the concise synthesis of anhydrolycorinone, a natural pyrrolophenanthridinone and a precursor of hippadine and anhydrolycorine.

A novel method for indole skeleton synthesis under mild conditions mediated by samarium(II) diiodide has been developed. The reaction of N-allenyl-2-iodoaniline derivatives with SmI2 in the presence of HMPA and i-PrOH at 0 °C afforded indole derivatives in high yields.

An efficient synthesis of 6-substituted 3-(alkoxycarbonyl)-5-aryl-α-pyrones is reported. This methodology consists of the successive manipulation of an addition–elimination reaction between benzyl ketone derivatives and dimethyl methoxymethylenemalonate, and an acid-catalyzed condensation reaction. The synthesis is applicable to various 5-p-substituted-aryl 6-substituted α-pyrones and good to excellent yields were obtained over two steps from benzyl ketone derivatives that were easily prepared from phenylacetic acid by the Negishi coupling or the Claisen decarboxylation reaction.

Dimethylsulfoxonium methylide (II) is prepared in situ from trimethylsulfoxonium iodide and sodium hydride.

In situ generated dimethylsulfoxonium methylide is used to synthesize the title compounds in moderate yields.

involving the stereoconvergent skeleton transformation from benzocyclobutapyranone (III) to dibenzofuran derivative (V) with dimethylsulfoxonium methylide as the key step

The synthesis proceeds via ketyl radical attack on the aromatic ring, single electron transfer, and nucleophilic attack of the resulting dienyl anion to the ester group.

Pyrido[1,2-a] benzimidazole derivatives (12a and 19a) were synthesized in moderate yields via an intramolecular aldol-condensation of 2-acetyl-1-formylmethylbenzimidazole (11) and an intramolecular acylation of the acylimidzolide (18) prepared from 2-ethoxycarbonylmethyl-1-(2-carboxyethyl)-benzimidazole (17), respectively

Photochemical Fries rearrangement of 1-phenyl-2-pyrrolidone (1) proceeded smoothly in methanol especially in the presence of piperylene. Continuous photo-irradiation of 1 successfully was carried out to raise the yield by utilizing a reaction mixture-circulation system consisting of a spiral quartz cell, a pump, a uv light source and a column packed with appropriate absorbents for the Fries rearranged product (3) and pigments

The reactions of 2-halogenonaphthoquinones (5, 13, 14 and 15) and 2-methyl-1, 4-naphthoquinone (20; vitamin K3) with primary and secondary amines were examined. 1, 3-Dialkyl-1, 2, 3, 4-tetrahydrobenzo[g]quinazoline-5, 10-diones (9) were obtained in moderate yields by treating 20 with formaldehyde in primary amines. A plausible reaction path-way is also presented.

Synthesis of 3-alkylamino-1, 4-naphthoquinone-2-carboxylic acid (2) was attempted. Although 3-(1-piperidinyl)-1, 4-naphthoquinone-2-carboxylic acid (2a) was not obtained, probably because of its instability, the esters (18a, b)of 2a could be prepared. 2-Alkylamino-3-hydroxymethyl-1, 4-naphthoquinones (9a-g) were photochemically cyclized to the 1, 4, 5, 10-tetrahydro-5, 10-2H-naphth[2, 3-d][1, 3]oxazines (19a-g), containing a novel heterocyclic ring system in moderate yields. Anti-bacterial activity of the prepared compounds was weak or insignificant.

3-Ethoxycarbonylcoumarin ( 4 ) was treated with 2.4 equivalent of dimethylsulfoxonium methylide in DMF at room temperature to give a novel tricyclic product, ethyl (3 a R ∗ , 8 b S ∗ )- 3a,8b-dihydro-3-hydroxy -1H- cyclopenta [b] benzofuran-2-carboxylate ( 5 ), in 64% yield. This reaction could be applied to several 3-substituted coumarins.

Cyclopropane ring of 2- and 2,3-substituted cyclopropanecarboxylates (1) was regioselectively cleaved using SmI 2 -HMPA-THF system in the presence of tert-BuOH to give 4- and 3,4-substituted butyrates (2) in moderate to good yields

Cyclic ketone O-trimethylsilylcyanohydrins (2) were prepared and converted to various compounds : α-hydroxyketones (3), dehydroxylated ketones (4), α, β-unsaturated ketones (9), tricyclic ketones (10), 1-ethoxycarbonyl-4-phenyl-1, 2, 4a, 5, 6, 7, 8, 8a-octahydro-2-naphthalenone (13), 1-phenylperhydroisocoumarin (18) and 1, 2, 3, 4, 4a, 10, 11, 11a-octahydro-5H-benzo[a, d]cyclohepten-10-one (20).

The cyclopropane ring in 2-substituted 1, 1-cyclopropanedicarboxylates was regioselectively opened by using samarium(II) diiodide (SmI2) in a hexamethylphosphoric triamide (HMPA)-tetrahydrofuran (THF) (1 : 10) system under mild and neutral conditions to give (2-substituted ethyl)malonates in moderate to good yields. The cyclopropane ring in 2-substituted cyclopropanecarboxylates or 2-substituted 3-(trimethylsilyl)cyclopropanecarboxylates was similarly cleaved regioselectively by using SmI2 in a HMPA-THF (1 : 1) system to give 4-arylbutyrates or 4-aryl-3-(trimethylsilyl)butyrates in 16-89% yields. The reaction mechanism of these ring-opening reactions is discussed.

α-Keto amides were dimerized in the presence of SmI2 in THF to give substituted tartaric amides in moderate to good yields. Although the dimerization of the secondary keto amides did not proceed stereoselectively, racemic tartaric amides were produced exclusively in the case of the tertiary keto amides.

Nortopsentins A-D, antifungal 1, 4-bisindolylimidazole marine alkaloids isolated from a sponge, were synthesized through palladium-catalyzed cross-coupling of 3-indolylboronic and 6-bromo-3-indolylboronic acids with halogenoimidazoles as the key reaction.

Trimethylsilylaion of 1, 2, 3-triazole regioselectively proceeded to give 2-trimethylsilyl-2H-1, 2, 3-triazole, which was treated with primary alkyl halides in the presence of tetrabutylammonium fluoride to give 1-alkyl-1H-1, 2, 3-triazoles as a sole product. 1-Methyl-5-substituted 1H-1, 2, 3-triazoles were prepared by alkylation of 5-lithio-1-methyl-1H-1, 2, 3-triazole, and 1-methyl-4-substituted 1H-1, 2, 3-triazoles were obtained by alkylaiton of 4-lithio-1-methyl-5-phenylthio-1H-1, 2, 3-triazole followed by reductive desulfurization.

In the presence of samarium diiodide, 2-aryl and 2-heteroaryl cyclopropane-1, 1-dicarboxylic esters were readily dimerized to give 3, 4-disubstituted 1, 1, 6, 6-hexanetetracarboxylic esters as diastereomeric mixtures in moderate to good yields. The diastereomeric mixtures were separated by preparative HPLC and stereo-chemistries of the isolated meso and racemic compounds were determined on the basis of HPLC analysis on chiral stationary phases. Between the 1H-NMR spectra of the separated diastereomers, the characteristic differences in the chemical shifts of the C2-H (C5-H) signals were observed and explained based on the MOPAC calculation.

The first total synthesis of clathridine A (8), a marine imidazole alkaloid, was achieved by using a novel regioselective condensation as a key step, in which preclathridine A (2) was treated with 1-methylparabanic acid (11) in the presence of a silylating agent.

Treatment of 1,3-dialkyl-2-(phenylthio)benzimidazolium salts 3 and 1,3-dialkyl-2-phenylthio-1H-imidazolium salts 7 with aq. K2CO3 gives 1,3-dialkyl-1,3-dihydrobenzimidazol-2-ones 4 and 1,3-dialkyl-1,3-dihydroimidazol-2-ones 8, respectively, in 22–94% yield. A regio-isomer 17 of kealiiquinone, a marine benzimidazole alkaloid, where the 4-methoxyphenyl group at the 4-position migrates to the 9-position, is synthesized by application of the reaction. Cytotoxity of 17 and kealiiquinone against 39 human cancer cells is evaluated. They have weak activity but a unique mechanism of action.

Diels–Alder-type dimerization of various 5-ethenyl-2-phenylsulfanyl-1 H -imidazoles provided a novel highly regio- and stereoselective route to the preparation of multifunctionalized 4,5,6,7-tetrahydrobenzimidazoles, the basic skeleton of ageliferin, a biologically active pyrrole–imidazole marine alkaloid. The reaction was applied to the synthesis of 12,12′-dimethylageliferin.

Eleven 3-substituted isocoumarins and a benzylidenephthalide were synthesized through thermal cyclization reaction of δ- and γ-ketoamides, respectively. Subsequent deprotection of the hydroxyl groups of the resulting isocoumarin and benzylidenephthalide compounds afforded thunberginols A, B, and F, respectively, which originated from the processed leaves of Hydrangea macrophylla SERINGE var. thunbergii MAKINO. The synthesized isocoumarins and thunberginols were evaluated for their anti-allergic activity, in which thunberginol B exhibited the highest inhibitory potency on the degranulation of RBL-2H3 cells induced by antigen. Structure–activity relationship studies were carried out to determine the necessary substituents on the 3-phenylisocoumarin skeleton for inhibitory activity.

We found two novel skeleton rearrangement reactions. The one was the reaction from coumarin derivatives having an electron-withdrawing group at the 3-position with dimethylsulfoxonium methylide to cyclopenta[b]benzofuran derivatives. The other was the reaction from benzo[b]cyclobuta[d]pyran derivatives having an electron-withdrawing group at the 2a-position to tetrahydrodibenzofuran derivatives. Interestingly, the latter reaction proceeded stereoconvergently regardless of the stereochemistry at the 1-position in the cyclobutane compounds. Driving forces of these reactions would be attributable to release of the ring strain including in a cyclopropane ring and cyclobutane ring. These methodologies were applied to the total synthesis of linderol A, which is a constituent of Lindera umbellata (Lauraceae) and has a potent inhibitory activity on melanin biosynthesis, and the synthesis was performed in 14 steps, 34% overall yield. Furthermore, the uncertain absolute structure of linderol A was determined, and its asymmetric synthesis was also achieved.

The novel skeleton transformation reaction of 2a-substituted 2a,8b-dihydrobenzo[ B]cyclobuta[ D]pyran-3-one derivatives into 2-(2-substituted 2-oxoethyl)-2 H-1-benzopyran derivatives has been accomplished using Znl 2 in the presence of an organic base and water in excellent yields.