Keiichi Yoneda

Synthesis of 3-methoxyquinolines via cyclization of 1-isocyano-2-(2-lithio-2-methoxyethenyl)benzenes

Abstract 2-(2-Isocyanophenyl)acetaldehyde dimethyl acetals were treated with excess LDA to generate 1-isocyano-2-(2-lithio-2-methoxyethenyl)benzenes, which cyclized intramolecularly to afford 3-methoxyquinolines in good to excellent yields.

One-Step Synthesis of Furo[2,3-d]Pyrimidine-2,4(1H,3H)-Diones Using the Can-Mediated Furan Ring Formation

Abstract The reaction of 1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione with various alkenes or terminal alkynes in the presence of cerium(IV) ammonium nitrate (CAN) afforded the corresponding 5,6-dihydrofuro[2,3-d]pyrimidine-2,4(1H,3H)-diones or furo[2,3-d]pyrimidine-2,4(1H,3H)-diones in moderate to good yields.

An improved method for the preparation of 4,7-dioxo-4,7-dihydrobenzo[b]thiophene-2-carboxylates from 2-acyl-1,4-benzoquinones and mercaptoacetates

4,7-Dioxo-4,7-dihydrobenzo[b]thiophene-2-carboxylates (4) have been synthesized in a one-pot procedure from 2-acyl-1,4-benzoquinones (1) and mercaptoacetates (2) by using 1-trimethylsilylimidazole as a protective reagent as well as a base. Thus, reaction of 1 with 2 in THF at room temperature was followed by treatment with excess of l -trimethylsilylimidazole at 80 °C. Then the cooled mixture was hydrolyzed with hydrochloric acid and oxidized with cerium(IV) ammonium nitrate (CAN) to give the expected thiophenequinone derivatives (4). 4,9-Dioxo-4,9-dihydronaphtho[2,3-b]thiophene-2-carboxylates (7) were similarly prepared from 2-acyl-1,4-naphthoquinones (5) and mercaptoacetates, in general, by omitting the CAN oxidation procedure.

Synthesis of Thienobenzofuranquinone Derivatives by Photoinduced and CAN-mediated 3+2-Type Cycloaddition Reactions

Photoinduced cycloaddition between ethyl 5-hydroxy-3-methyl-4,7-dioxo-4,7-dihydrobenzo[b]thiophene-2-carboxylate (la) and alkenes is reported to give ethyl 7-methyl-4,8-dioxo-2,3,4,8-tetrahydrothieno[2,3-f]benzofuran-6-carboxylates (2). Cerium(IV) ammonium nitrate (CAN)-mediated cycloaddition of ethyl 5-hydroxy-4,7-dioxo-4,7-dihydrobenzo[b]thiophene-2-carboxylates (1) to alkenes or phenylacetylene, giving ethyl 4,8-dioxo-4,8-dihydrothieno[2,3-f]benzofuran-6-carboxylate (2 or 4) and ethyl 4,5-dioxo-4,5-dihydrothieno[3,2-g]benzofuran-7-carboxylate derivatives (3 or 5), is also reported.

An efficient method for the one-pot construction of the 1H-naphtho[2,3-c]pyran-5,10-dione system

2-(1-Hydroxyalkyl)-1,4-naphthoquinones are found to react with pyrrolidino enamines in toluene to give 1H-naphtho[2,3-c]pyran-5,10-diones in good yields via a tandem conjugate addition–cyclization sequence, followed by an elimination of pyrrolidine. 2-Hydroxymethyl-1,4-naphthoquinone and morpholino enamines undergo a similar sequence, without loss of morpholine, to yield 3-morpholino-3,4-dihydro-1H-naphtho[2,3-c]pyran-5,10-diones. The 3-morpholino group of these products can be replaced with a hydro, a hydroxy, or a methoxy group. Imines also react with 2-(1-hydroxyalkyl)-1,4-naphthoquinones to give the corresponding 1H-naphtho[2,3-c]pyran-5,10-diones, including a natural product (pentalongin). The utility of these reactions is demonstrated in the synthesis of pyranonaphthoquinone antibiotics, viz. (±)-eleutherin and (±)-isoeleutherin.