Francisco Fariña

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.

Pseudoesters and derivatives. XXIII Reaction of 3-bromo-5-methoxyfuran-2(5H)-one with nucleophiles. Formation of cyclopropane derivatives

Abstract The reactions of 3-bromo-5-methoxyfuran-2 (5 H )-one ( 1 ) with nucleophiles in acetonitrile, in the presence of potassium carbonate and tetrabutylammonium bromide as a catalyst, are reported. The bromofuranone 1 reacts, with several carbon and oxygen nucleophiles to give the cyclopropane bis-lactones 7 , 8 , 11 or 12 . When 1 is reacted with diethylamine or propane-2-thiol in a 2:1 ratio, similar cyclopropane bis-lactones 16 or 21 , respectively, are formed. This behaviour is explained on the basis of a mechanism involving a double Michael addition, followed by ring closure via internal nucleophilic substitution of the halogen.

1,3-Dipolar cycloaddition of nitrile oxides to 2(5H)-furanones substituted at the 5-position by sulphur bearing groups

Abstract The behavior of the furanones 1–4 towards nitrile oxides 5–7 has been investigated, in particular with respect to the regio- and stereoselectivity. Cycloaddition of benzonitrile oxide (5) to 4,5-diethylsulphonylfuran-2(5H)-one (12) leads as sole addition product to the isoxazoline 30, that was easily aromatized to the isoxazole derivative 31, which is a useful synthon for the preparation of heteroanthracyclinone analogues.

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.

Pseudoesters and Derivatives. XXXI1. Synthesis of 5-Ethylthio-, 5-Ethylsulfinyl- and 5-Ethylsulfonylfuran-2(5H)-ones

Abstract Convenient syntheses of 5-(ethylthio) furan-2(5H)-ones 2a-k from the appropriate 5-methoxyfuran-2(5H)-one 1a-g are described. The oxidation to the corresponding sulfoxides 5a-c and sulfones 6a-f is also reported.

Polycyclic hydroxyquinones. XIX: Regiospecific synthesis of anthracyclinones via the Diels-Alder reaction with dichloronaphthazarins

Abstract A convenient route to the daunomycinone precursor 18 via a succession of Diels-Alder reactions from 2,7-dichloronaphthazarin (9) is described. In a similar manner, starting from 2,6-dichloronaphthazarin (19) compound 20, a regioisomer of 18,is synthesized. This methodology constitutes a regiospecific approach to (±)-daunomycinone and related anthracyclinones.

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.