Peter R. K. Mitchell

Naphtho[2,3-c]pyran-5,10-quinones. Syntheses of the racemates of quinone A, quinone A′, and deoxyquinone A dimethyl ethers of 7-methoxyeleutherin, and of isoeleutherin

Treatment of 3-(1-hydroxyethyl)-1,4,5,7-tetrarmethoxy-2-prop-2-enylnaphthalene (33) with potassium t-butoxide in dimethylformamide under nitrogen for a short time gave a high yield of trans-3,4-dihydro-5,7,9,10-tetramethoxy-1,3-dimethyl-1H-naphtho[2,3-c]pyran (41). This compound, with the same base and solvent, but in air, afforded a mixture comprising its cis-epimer (42), together with the two possible 4-hydroxy derivatives, namely (35) and (38). Silver(II) oxide oxidation of compounds (35), (38), (41), and (42) gave, respectively, the dimethyl ethers of quinone A, quinone A′, and deoxyquinone A, and also 7-methoxyeleutherin.

The syntheses of (±)-juglomycin A and (±)-juglomycin B, racemates of two isomeric naturally occurring naphthoquinonoid antibiotics

Syntheses of the diastereoisomeric 5-hydroxy-2-(4′-hydroxy-γ-butyrolacton-5′-yl)-1,4-naphthoquinones (1) and (2) and their 5-deoxy-analogues (3) and (4) are described. The stereochemistries of the latter, being defined through unambiguous synthesis, permit the assignment of the configurations of (1) and (2)(which were obtained from a single precursor) and also those of the natural products, juglomycins A and B.

Base-induced cyclisations of naphthalenes into naphtho[2,3-c]pyrans. Application to stereospecific syntheses of (±)-isoeleutherin and (±)-deoxyquinone a dimethyl ether

2-(Alk-2-enyl)-3-(1-hydroxyalkyl)-1,4-dimethoxynaphthalenes are cyclised and then oxidised to naphtho[2,3-c]pyran-5,10-quinones which are naturally occurring quinones or their derivatives.

Synthesis of the aphin-related (±)-7,9-dideoxyquinone A and (±)-7,9-dideoxyquinone A′

The oxidative cyclisation of 3-(1-hydroxyethyl)-,1,4-dimethoxy-2-prop-1-enylnaphthalene with four equivalents of ceric ammonium nitrate to afford two 4-hydroxy-1,3-dimethylnaphtho[2,3-c]pyran-5,10-quinones with the same stereochemistry as quinones A and A′, derivatives of the aphid pigments protoaphin-fb and protoaphin-sl, is described. Certain aspects of the mechanism have been established.

Naphthopyrans by ring-closure of substituted naphthalenes using potassium t-butoxide in dimethylformamide

Two 2-alkenyl-3-hydroxyalkyl-1,4-dimethoxynaphthalenes are cyclised with potassium t-butoxide in dimethylformamide to give 3-alkyl-3,4-dihydro-5,10-dimethoxynaphtho [2,3-c] pyrans under anaerobic conditions. One of these products is treated with the same solvent and base, but in air, to give the two possible 4-hydroxy derivatives.

Approaches to the synthesis of 4-hydroxypiloquinone

The synthesis of 4-acetoxy-1,8-dihydroxy-2-methyl-3-(4-methylpentanoyl)phenanthrene-9,10-quinoee (30) and 1,4,8-trimethoxy-2-methyl-3-(4-methylpentanoyl)phenanthrene-9,10-quinone (33), derivatives of the mould metabolite 4-hydroxypiloquinone [1,4,8-trihydroxy-2-methyl-3-(4-methylpentanoyl)-phenanthrene-9,10-quinone](2) are described. Photocyclization of methyl 2,2′,5,6′-tetramethoxy-3-methylstilbene-4-carboxylate (21) provided methyl 1,4,8-trimethoxy-2-methylphenanthrene-3-carboxylate (22), suitable for further elaboration into the natural derivatives.

Regioselective bromination, debromination and bromine migration in a 2-acetoxymethyl-4,5,7-trialkoxynaphthalene

Dibromination of 2-acetoxymethyl-4-isopropoxy-5,7-dimethoxynaphthalene 10 in buffered solution afforded the 3,8-dibromo derivative 13. Similar monobromination of compound 10 yielded the 8-bromo compound 15, whereas monobromination in the absence of the buffer yielded the isomeric 1-bromonaphthalene 16. Conversion of 15 into 16 was effected with trifluoroacetic acid. Selective monodebromination of the dibromo compound 13 gave rise to a third isomer, the 3-bromo compound 18.

An abnormal fries rearrangement induced by a -methoxyl group in monoacetates of naphthohydroquinones.

Abstract The acetyl group of two 1-acetoxy-4-hydroxy-5-methoxynaphthalenes migrates to C-3 on treatment with boron trifluoride etherate.

Syntheses of naphtho[2,3-c]pyran-5,10-quinones using ceric ammonium nitrate

Two 2-(alk-1-enyl)-3-(1-hydroxyalkyl)-1,4-dimethoxynaphthalenes are oxidised with silver(II) oxide to the corresponding naphthoquinones, while oxidation with cerium(IV) ammonium nitrate affords derivatives of the title compounds.

A photochemical reaction of 2-acetyl-3-alkylamino-1,4-benzoquinones: formation of benzoxazoles

A number of 2-acetyl-3-alkylamino-6-anilino-1,4-benzoquinones have been prepared by the reaction of 2-acetyl-3,6-dianilino-1,4-benzoquinone with alkylamines in chloroform solution. Irradiation of 3-methylamino-, 3-n-propylamino-, and 3-phenethylamino-2-acetyl-6-anilino-1,4-benzoquinones in solution gave benzoxazoles and 2-acetyl-3-amino-6-anilino-1,4-benzoquinone.