M. Carmen Paredes

Synthesis of anthraquinone derivatives by palladium-catalyzed coupling of triflates with stannanes

Abstract The palladium-catalyzed coupling of hydroxyanthraquinone triflates with stannanes provides an efficient entry into substituted anthraquinones under neutral conditions.

Synthesis of 3,4-Dihydro-4-Hydroxy-2,2-Dimethyl-2H-1-Benzopyran-5 8-Dione. A Potential Key Intermediate for the Preparation of Naphtho[2,3-b]Pyranoquinones

Abstract The synthesis of pyranoquinone 6 and its application to the elaboration of pyranonaphthoquinone 1b is described.

Polycyclic hydroxyquinones—VIII: Preparation of acetylhydroxynaphthazarins by photo-fries rearrangement. A convenient synthesis of spinochrome A

Abstract Several synthetic routes to mono- and dihydroxynaphthazarins bearing an acetyl side-chain have been explored. Methoxynaphthazarin 1 has always been the starting material. Acylation is brought about via a photo-Fries rearrangement of various adequately substituted acetoxynaphthalenes prepared in several steps from 1 . Further steps including oxidative demethylation, hydrolysis and ether cleavage reactions, led to the desired mono- and dihydroxysubstituted acetylnaphthazarins. A new synthesis of Spinochrome A 24 , a natural occurring pigment representative of this kind of naphthazarin derivatives, is described.

Studies on Quinones. XVIII1. Synthesis of Diels-Alder Adducts of Activated Quinones with (E)-1-trimethylsilyloxybuta-1,3-diene

Abstract The synthesis of several angular Diels-Alder adducts of activated quinones with (E) - 1-trimethyl-silyloxybuta-1,3-diene, is described.

Studies on quinones. Part 21. Regioselective synthesis of tetracyclic quinones related to rabelomycin

The Diels–Alder reaction of the hydroxyquinones 5,11 and 16 with (E)-1 -trimethylsiloxybuta-1,3-diene 3 afforded the corresponding mixture of the regioisomers 6a,b, 12a,b and 17a, b in the ratios 9:1, 8:1 and 11:1, respectively. From these mixtures, the quinones 8, 14 and 19 were obtained by hydrolysis and subsequent oxidation.The preparation of the diene 22 by chlorotrimethylsilylation of the anion of the ester 21 is described. Diels–Alder reaction of diene 22 with the quinones 23 and 24 yielded the corresponding 6-ethoxybenz[a]anthracenequinones 25 and 26, together with the 6-hydroxybenz[a]anthracenequinones 19 and 20. The quinones 19 and 20, which were isolated in mixtures with the ester 21, undergo selective aerial oxidation under basic conditions to give the corresponding benz[a]anthracene-1,7,12-triones 27 and 28.

Polycyclic hydroxyquinones : XXIV Diels-alder reactions of 5-amino-8-hydroxy-1,4-naphthoquinone. Novel transcycloaddition reactions with derivatives of 1,4-dihydro-1, 4-methanoanthracene-9,10-dione

Abstract Diels-Alder reactions of 5-amino-8-hydroxy-1, 4-naphthoquinone ( 1 a ) and derivatives ( 1 b - e ) with cyclopentadiene and 2, 3-dimethylbuta-1, 3-diene afford the corresponding adducts 2 a - e and 4 a - e in good yields. Adducts 2 a and 4 a , by oxidation under alkaline conditions in the presence of air, are converted into quinones 3 a and 5 a , respectively. Quinone 3 a undergoes a novel transcycloaddition reaction with 2, 3-dimethylbuta-1, 3-diene, which involves cycloaddition to give the angular adducts 7 n and 7 x , followed by cycloreversion to afford 5 a and cyclopentadiene. Quinone 3 a similarly undergoes a transcycloaddition with diazomethane to yield a single benz [ f ] indazol 9 . The reverse regiochemistry is observed starting from the O , N -diacyl derivative 3 e . Similar transcycloadditions with 5, 8-dimethoxy-1, 4-dihydro-1, 4-methanoanthracene-9, 10-dione are reported.

Synthesis, tautomerism and Diels-Alder reactions of 1,4-dihydroxy-9, 10-anthraquinon-9-imines

Abstract The ammonolysis of quinizarin and simple derivatives thereof affords 9-imino-derivatives, the tautomeric forms of which act as dienophiles in Diels-Alder reactions to yield tetracyclic compounds of potential value as anthracyclinone precursors.

Studies on quinones. 24. Rearrangement of Diels-Alder adducts of activated quinones under acidic conditions

Abstract The Diels-Alder adducts 4 , 19 , 9 , 10 , 8 , 11 , of benzoquinones bearing activating groups (COCH 3 COCH=CHPh, CO 2 Me, NO 2 CHO, CN) by treatment with 1,3 N hydrochloric acid are initially converted into the dihydrobenzofurans 7 , 22 , the corresponding alcohols 12 , 13 or the arylcrotonaldehydes 14 , 15 , respectively. By treatment with 8.5 N hydrochloric acid, adducts 8–10 are converted directly into the corresponding dihydrobenzofurans. In the presence of silica gel, adduct 19 is partially converted into the benzocyclooctatriene derivative 21 . The alcohol 26 , formed by hydrolysis of adduct 25 , rearranges to the benzodifuran derivatives 28 and 29 in the presence of silica gel and ethanol or methanol, respectively.

Regiospecific Addition of Alcohols to 9-Hydroxy-and 9-Methoxy-1, 4-Anthraquinone

Abstract Conjugated addition of alcohols to 9-hydroxy-and 9-methoxy-1, 4-anthraquinone, in the presence of a strong acid and an oxidant, affords the 2-alkoxy- and 3-alkoxy-substituted regioisomer, respectively.

Polycyclic hydroxyquinones. XXVII. Tautomerism in 1,4-Dihydroxy-9,10-anthraquinone Monoimines. Cycloaddition Reactions of Their 1,4-Anthraquinonoid Tautomers☆

Abstract 1,4-Dihydroxy-9,10-anthraquinone monoimine and differently substituted derivatives thereof ( 6a-i ) have been prepared by ammonolysis of the corresponding 1,4-dihydroxy-9,10-anthraquinones. 1 H- and 13 C-n.m.r. studies show the existence of a rapid tautomeric equilibrium in quinone imines of type 6 . Diels-Alder reaction with the 1,4-anthraquinonoid tautomer of quinone monoimines 6a,e affords ABCD tetracyclic systems related to those existing in anthracyclinones.