Tomokazu Uneda

One-pot synthesis of naphtho[2,3-b]furan-4,9-diones by sequential coupling/ring closure reactions

Abstract Treatment of 3-phenyliodonio-1,2,4-trioxo-1,2,3,4-tetrahydronaphthalenides with terminal acetylenes in the presence of a bis(triphenylphosphine)palladium chloride-cuprous iodide catalyst or cuprous oxide in N -methylpiperidine or pyridine, respectively, furnished the corresponding 2-substituted naphtho[2,3- b ]furan-4,9-diones in moderate to good yields. The utility of this method was demonstrated in the synthesis of a cytotoxic natural product, 2-(1-hydroxyethyl)naphtho[2,3- b ]furan-4,9-dione.

One-pot preparation of 1H-naphtho[2,3-c]pyran-5,10-diones and its application to concise total synthesis of (±)-eleutherin and (±)-isoeleutherin

Abstract 1H-Naphtho[2,3-c]pyran-5,10-dione derivatives, including a natural product (pentalongin), were generally synthesized in one-pot using a tandem conjugate addition-cyclization sequence between 2-(1-hydroxyalkyl)-1,4-naphthoquinones and enamines (or imines). The utility of this method was demonstrated in the synthesis of pyranonaphthoquinone antibiotics, (±)-eleutherin and (±)-isoeleutherin.

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.

A simple method for the synthesis of 4-aryl-9-oxynaphthofuranone lignans

The 9-aryl-4-oxynaphthofuran-1(3H)-one system is generally synthesized in two steps from α-aryl-o-toluic acid derivatives. The method involves a tandem conjugate addition–Dieckmann type condensation between α-lithiated α-aryl-o-toluic acid derivatives and 2-furan-2(5H)-one as a key step followed by simple dehydrogenation or dehydration, and can be applied to the synthesis of two natural lignans (neojusticidin A and neojusticidin B).