Browsing by Author "VALDERRAMA, JA"
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- ItemDIENONE PHENOL REARRANGEMENT MECHANISM OF 8,8-DIMETHYL-NAPHTHALENE-1,4,5(8H)-TRIONES AND 6,8,8-TRIMETHYL-NAPHTHALENE-1,4,5(8H)-TRIONES IN ACETIC-ANHYDRIDE SOLUTION(1988) GOYCOOLEA, C; SANTOS, JG; VALDERRAMA, JA
- ItemKINETIC-STUDIES ON THE REARRANGEMENT OF DIELS-ALDER ADDUCTS OF ACTIVATED BENZOQUINONES WITH (E)-1-TRIMETHYLSILOXYBUTA-1,3-DIENE(1993) SANTOS, JG; ROBERT, P; VALDERRAMA, JAThe acid-induced rearrangement of the 4a-derivatives of 4a,5-trans-4a,8a-cis-5-trimethylsiloxy-4a,5,8,8a-tetrahydro-1,4-naphthoquinones 4-6 in dioxane-water and THF-water solutions is the subject of a kinetic study. On the basis of spectrophotometric evidence, the incursion of 5-hydroxy-tetrahydronaphthalene-1,4-dione and arylcrotonaldehyde type intermediates in formation of the benzofuran from adducts 4-6, is proposed. The effects on the reactions of the solvent composition, temperature, hydrochloric acid concentration, and substituent nature in the adducts are discussed. The results are rationalized and a schematic representation is provided.
- ItemNEW SYNTHESIS OF URACIL AND 2-THIOURACIL(1984) CASSIS, R; TAPIA, R; VALDERRAMA, JA
- ItemNITRIC-ACID ON SILICA-GEL - A USEFUL NITRATING REAGENT FOR ACTIVATED AROMATIC-COMPOUNDS(1986) TAPIA, R; TORRES, G; VALDERRAMA, JA
- ItemON THE REARRANGEMENT MECHANISM OF CYCLIC O,N-ACETALS DERIVED FROM ACYLQUINONES AND ENAMINES(1986) CASTRO, CG; SANTOS, JG; VALDERRAMA, JA
- ItemSTUDIES ON QUINONES .18. SYNTHESIS OF DIELS-ALDER ADDUCTS OF ACTIVATED QUINONES WITH (E)-1-TRIMETHYLSILYLOXYBUTA-1,3-DIENE(1989) VALDERRAMA, JA; FARINA, F; PAREDES, MC
- ItemSTUDIES ON QUINONES .21. REGIOSELECTIVE SYNTHESIS OF TETRACYCLIC QUINONES RELATED TO RABELOMYCIN(1991) VALDERRAMA, JA; ARAYA-MATURANA, R; GONZALEZ, MF; TAPIA, R; FARINA, F; PAREDES, MCThe 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.
- ItemSTUDIES ON QUINONES .24. REARRANGEMENT OF DIELS-ALDER ADDUCTS OF ACTIVATED QUINONES UNDER ACIDIC CONDITIONS(PERGAMON-ELSEVIER SCIENCE LTD, 1992) FARINA, F; PAREDES, MC; VALDERRAMA, JAThe Diets-Alder adducts 5, 19, 9, 10, 8, 11, of benzoquinones bearing activating groups (COCH3, COCH=CHPh, CO2Me, NO2, 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.
- ItemSTUDIES ON QUINONES .26. THE REACTION OF METHACROLEIN N,N-DIMETHYLHYDRAZONE WITH ACTIVATED BENZOQUINONES(1993) VALDERRAMA, JA; GONZALEZ, MFA one-step formation of 5-hydroxy-2,3-dihydrobenzo[b]furans by a [3+2] addition process of methacrolein N,N-dimethylhydrazone (4) with a variety of 1,4-benzoquinones bearing activating groups is reported.
- ItemSTUDIES ON QUINONES .27. DIELS-ALDER REACTION OF 8,8-DIMETHYLNAPHTHALENE-1,4,5(8H)-TRIONE(1993) VALDERRAMA, JA; ARAYA-MATURANA, R; ZULOAGA, FThe Diels-Alder reaction of the title quinone 1 with various symmetrical and unsymmetrical dienes in ethanol solution is reported. The cycloaddition takes place, in all cases, across the external quinone double bond affording with cyclopentadiene, buta-1,3-diene and 2,3-dimethylbuta-1,3-diene, the corresponding adducts 3, 4 and 5. The cycloaddition of 1 with 2-methylbuta-1,3-diene and penta-1,3-diene provided 90:10 and 65:35 mixtures of regioisomers 6-7 and 17-18, respectively. Enolisation of these adduct mixtures afforded the corresponding anthracenones 10-11 and 21-22. Compounds 11 and 22, the minor components of the anthracenone mixtures, were synthesized from acetylnaphthalenes 14 and 23.
- ItemSTUDIES ON QUINONES .28. NOVEL REARRANGEMENTS OF DIELS-ALDER ADDUCTS OF NAPHTHO-DIQUINONES AND ANTHRADIQUINONES(1993) FARINA, F; PAREDES, MC; VALDERRAMA, JAThe Diels-Alder adducts 7a,b by acidic hydrolysis afford the alcohols 8a,b, which in the presence of silica gel, rearrange into the quinizarin derivative 10a and minor amounts of the naphthofuran 11. The rearrangement of 8a,b with silica gel in the presence of ethanol affords the naphthofuran type products 12 and 15. The thermal rearrangement of alcohols 8a,b by heating in benzene solution affords a mixture of the rearranged products 10a,b and the spirocompound 18. Under similar thermal conditions, the alcohol 3 produced the leuconaphthazarin derivative 19 and the spirocompound 20.
- ItemSYNTHESIS OF 2,2-DIMETHYL-2H-CHROMENES(1984) CORTES, MJ; HADDAD, GR; VALDERRAMA, JAThe antijuvenile hormones precocenes I and II, and related 2,2-dimethyl-2H chromenes were synthesized by oxidative cyclization of o-isoprenylphenols with m-chloroperbenzoic acid, followed by dehydration of the corresponding 3-chromanols with methyltriphenoxyphosphonium iodide.