Sadamu Katayama

Hetero-Diels–Alder reactions of 2-methylene-1,3-dicarbonyl compounds with alkyl vinyl ethers

2-Methylene-1,3-dicarbonyl compounds reacted with alky vinyl ethers in benzene to give hetero-Diels–Alder reaction products, 3,4-dihydro-2H-pyrans, regioselectively and/or chemoselectively.

Total synthesis of fulvic acid

Synthesis of fulvic acid (1a) was accomplished by a route involving selective ozonization of 9-propenylpyranobenzopyran (1c), obtained by a regioselective cyclization of the 2-methylsulphinylmethyl 1,3-dione(3c).

Reactivity of 2-methylene-1,3-dicarbonyl compounds. Inverse electron-demand Diels–Alder reactions with alkyl vinyl ethers

Highly regioselective hetero-Diels–Alder reactions were achieved by reaction of 2-methyene-1,3-dicarbonyl compounds 1 with alkyl vinyl ethers 2. This regioselectivity of the cycloadditions was consistent with the results that could be predicted by considering the frontier orbital of 1.

Studies on the syntheses of heterocyclic compounds containing benzopyrone. Part 5. Total synthesis of fulvic acid

Total synthesis of fulvic acid (1a) is described. Regioselective cyclization of the enedione (8f), an equivalent of the proposed biogenetic intermediate (5a) for citromycetin (2), gave the pyrone (11a), which led to fulvic acid (1a) by a route involving debenzylation, selective ozonization, and hydration.

Regiospecific (biogenetic-type) synthesis of 2-methyl-5H-pyrano[3,2-c][1]benzopyran-4-one, the basic skeleton in citromycetin

Regiopspecific cyclization of the acetal (4g), derived in 5 steps from 2′-benzyloxyacetophenone (3a), gave the pyrone (6a), which was easily converted into 2-methyl-5H-pyrano[3,2-c][1]benzopyran-4-one (1b), the basic skeleton in citromycetin (1a).

Synthesis of bicyclo[4.1.0]hept-2-enes (trinorcarenes) by photochemical reaction of bicyclo[2.2.2]oct-5-en-2-ones

Photochemical reaction of bicyclo[2.2.2[oct-5-en-2-ones has been investigated as a prelude to focused application to the synthesis of sesquiterpenes such as sesquicarene and sirenin. Diels–Alder reaction of cyclohexa-2,4-dienes, having different substituents (methylthiomethyl and methoxy) at the C-6 position, with a dienophile proceeds regio- and stereo-selectively to give bicyclo[2.2.2]oct-5-en-2-ones; their photolysis in benzene upon high-pressure Hg lamp irradiation affords decarbonylation products, bicyclo[4.1.0]hept-2-enes (trinorcarenes), stereoselectively. Replacement of the methylthiomethyl group with a 2-ethoxycarbonylvinyl group improves the sequential reaction.

Studies on the syntheses of heterocyclic compounds containing benzopyrone. Part 6. Biomimetic total synthesis of citromycetin

Biomimetic total synthesis of citromycetin (1a) is described. Regioselective cyclization of the enetrione (5), chosen as a common intermediate for the syntheses of citromycetin (1a) and fulvic acid (2a), with conc. HCI–AcOH (1:30) gave the chioromethylpyrone (7b). Oxidation, followed by demethylation of the substituents of the pyranobenzopyranone obtained by debenzylation and cyclization of the reactive intermediate (5), yielded citromycetin (1a).

Studies on the synthesis of heterocyclic compounds containing benzopyrone. Part 4. Synthesis of 4,10-dihydro-3-hydroxy-3-methyl-1H,3H-pyrano[4,3-b][1] benzopyran-10-one, the basic skeleton in fulvic acid

The synthesis of 4,5-dihydro-3-hydroxy-3-methyl-lH,3H-pyrano[4,3-b][1]benzopyran-10-one (1b), the basic skeleton in fulvic acid, is described. The acetal (4), chosen as a common intermediate for syntheses of the basic skeletons in fungal metabolites such as fulvic acid and citromycetin, was cyclized into the dihydropyrone (7) with 5% HCl-tetrahydrofuran (1 : 2) regioselectively. Debenzylation followed by cyclization of the boron complex of (7) gave the tricyclic pyrone [2b], which was converted into the benzopyranone (1b) with 5% HCl–(1 : 1)

Biogenetic-type total synthesis of citromycetin

Biogenetic-type total synthesis of citromycetin (1a) was achieved by a route involving oxidation of a propenyl group and demethylation of a methoxy group in the pyranobenzopyranone (1c), synthesized by a regioselctive cyclization of the enedione (2c).

Studies of the syntheses of heterocyclic compounds containing benzopyrone. Part 3. Synthesis of 2-methyl-4H,5H-pyrano[3,2-c][1]benzopyran-4-one, the basic skeleton in citromycetin

The synthesis of 2-methyl-4H,5H-pyrano[3,2-c][1]benzopyrano-4-one (1b), the basic skeleton in citromycetin, is described. The alcohol (6a), chosen as the starting material, was oxidized to the dione (6c) which, after methylenation, was treated with concentrated hydrochloric acid–methanol (1 :100) at ambient temperature to afford the pyrone (9a) regioselectively. Hydrogenation and bromine substitution of the pyrone (9a) gave the bromide (9e), which was converted into the benzopyranone (1b) with aqueous sodium hydrogen carbonate.