Showing papers by "J. Carlos Menéndez published in 1998"
TL;DR: In this paper, the transformation of 3-arylmethylenepiperazine-2,5-diones (1) into 1-ylmethylene-2.4-dihydro-1H-pyrazino[2,1-b]quinazoline-3,6-dionses (2) was studied.
26 citations
TL;DR: In this article, the cyclization of all four diastereoisomers of cyclo-Ala to the corresponding 3,5a,6,10b,11,11a-hexahydro-2 H -pyrazino[2′,1′-5,1]pyrrolo[2,3-b ]indoles is studied from the stereochemical point of view.
Abstract: The cyclization of all four diastereoisomers of cyclo -(Trp-Ala) to the corresponding 3,5a,6,10b,11,11a-hexahydro-2 H -pyrazino[2′,1′-5,1]pyrrolo[2,3- b ]indoles is studied from the stereochemical point of view. Epimerization of the tryptophan stereocenter during the cyclization and during acylation reactions of the N-2 atom of the tetracyclic derivatives is discussed.
22 citations
TL;DR: In this article, an efficient synthesis of quinoline-2,5,8(1H)-triones bearing alkyl groups at C3 and/or C4 is described.
Abstract: An efficient synthesis of quinoline-2,5,8(1H)-triones bearing alkyl groups at C3 and/or C4 is described. The reaction sequence employed involves Knorr cyclization of 2,5-dimethoxyanilides into 5,8-dimethoxyquinoline systems, followed by oxidative demethylation with cerium ammonium nitrate. The starting 2,5-dimethoxyanilides were prepared by chemoselective acylation by regioselective alkylation of S-tert-butyl acetothioacetate (1) at C2 and/or C4. The introduction of electrophiles other than alkyl groups at C2 on 1 was also studied.
14 citations
TL;DR: In this article, a double hetero Diels-Alder reaction between 2,6-dibromobenzoquinone and 2,methyl-2-hexenal dimethylhydrazone, aromatiztion by a novel, one-pot N-oxidation/elimination procedure with percarbamide in trifluoroacetic acid, and double N -oxidation followed by rearrangement to a double lactam system.
13 citations
TL;DR: In this article, the reaction between 6-acetyl-3-alkyl-1-ethoxy, 3,4,5a,6,11,11a-hexahydro-10b H -pyrazino and anthranilic acid was studied from a stereochemical point of view.
Abstract: The reaction between 6-acetyl-3-alkyl-1-ethoxy-3,4,5a,6,11,11a-hexahydro-10b H -pyrazino-[2′,1′-5,1]pyrrolo[2,3- b ]indole-1,4-diones and anthranilic acid was studied from a stereochemical point of view. Various degrees of epimerization of the tryptophan and alanine stereocenters were observed in compounds with a cis relationship between their H-3 and H-11a hydrogen atoms, and stereochemistry was retained in the trans compounds. These observations are explained in terms of steric compression between the C 5 O, C 7 –alkyl and C 8 O groups in the hexacyclic reaction products. Acylation at N-2 with o -azidobenzoyl chloride followed by an intramolecular aza Wittig reaction afforded the target 10-acetyl-5,7,8,9a,10,14b,15,15a-octahydroindolo[3″,2″-4′,5′]pyrrolo[2′,1′-3,4]pyrazino[2,1- b ]quinazoline-5,8-diones with retention of all stereocenters.
10 citations