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Ethyl 7-Acetyl-8a-methyl-3-(1-phenyl-1H-tetrazol-5-yl)-1,4,4a,5,6,8a-hexahydro-...
Lopes, Susana M. M.; Lemos, Américo; Paixão, José A.; Melo, Teresa M. V. D. Pinho eThe Diels–Alder reaction of ethyl 3-(1-phenyl-1H-tetrazol-5-yl-1,2-diaza-1,3-butadiene- 1-carboxylate with 2-acetyl-6-methyl-2,3-dihydro-4H-pyran (methyl vinyl ketone dimer) regios- electively afforded the corresponding 3-(tetrazol-5-yl)-hexahydro-7H-pyrano[2,3-c]pyridazine in quantitative yield. An X-ray crystal structure of this cycloadduct is reported.
One-Pot Synthetic Approach to Dipyrromethanes and Bis(indolyl)methanes via Nitr...
Cardoso, Ana L.; Lopes, Susana M. M.; Grosso, Carla; Pineiro, Marta; Lemos, Américo; Pinho e Melo, Teresa M. V. D.A one-pot regio- and stereoselective synthesis of a dipyrromethane and a bis(indolyl)methane based on two consecutive reactions of nitrosoalkenes with pyrrole or indole, respectively, is described as an experiment to be carried out by upper-division undergraduate students in a laboratory classroom. Importantly, the ability of electrophilic conjugated nitrosoalkenes to react via Michael addition or hetero-Diels−...
Asymmetric Neber Reaction in the Synthesis of Chiral 2-(Tetrazol-5-yl)-2H-Azirines
Alves, Cláudia; Grosso, Carla; Barrulas, Pedro; Paixão, José; Cardoso, Ana; Burke, Anthony; Lemos, Américo; Pinho e Melo, TeresaA successful one-pot methodology for the synthesis of chiral 2-tetrazolyl-2H-azirines has been established, resorting to organocatalysis. The protocol involves the in situ tosylation of β-ketoxime-1H-tetrazoles followed by the Neber reaction, in the presence of chiral organocatalysts. Among the organocatalysts studied a novel thiourea catalyst derived from 6β-aminopenicillanic acid afforded excellent enantiosel...
Asymmetric Neber Reaction in the Synthesis of Chiral 2-(Tetrazol-5-yl)-2H-Azirines
Alves, Cláudia; Grosso, Carla; Barrulas, Pedro; Paixão, José A.; Cardoso, Ana L.; Burke, Anthony J.; Lemos, Américo; Melo, Teresa M. V. D. Pinho eA successful one-pot methodology for the synthesis of chiral 2-tetrazolyl-2H-azirines has been established, resorting to organocatalysis. The protocol involves the in situ tosylation of β-ketoxime-1H-tetrazoles followed by the Neber reaction, in the presence of chiral organocatalysts. Among the organocatalysts studied a novel thiourea catalyst derived from 6β-aminopenicillanic acid afforded excellent enantiosel...
Functionalization of dipyrromethanes via hetero-Diels–Alder reaction with azo- ...
Pereira, Nelson A. M.; Lemos, Américo; Serra, Arménio C.; Melo, Teresa M. V. D. Pinho e5,5′-Diethyl- and 5-phenyldipyrromethanes participate in cycloadditions with azo- and nitrosoalkenes giving dipyrromethanes with side chains containing open chain oximes and hydrazones. By controlling reaction stoichiometry it is possible to get mono or 1,9-disubstituted derivatives. The reported methodology gave access to a range of dipyrromethanes with good structural features for various applications. It was...
Ethyl 3-(2-pyridyl)-2H-azirine-2-carboxylate : synthesis and reactivity with di...
Alves, M. José; Fortes, A. Gil; Lemos, Américo; Martins, Cristina I.Ethyl 3-(2-pyridyl)-2H-azirine-2-carboxylate, the first example of an 3-heteroamatic-2H-azirine, was prepared and its reaction with conjugated 1,3-dienes, under mild conditions and in the absence of Lewis acid catalyst, produced cycloadducts in good yield and high stereoselectivity.
Intermolecular alkyl radical addition to methyl 2-(2,6-dichlorophenyl)-2H-aziri...
Alves, Maria José Chão; Fortes, A. Gil; Guimarães, Emanuel; Lemos, AméricoThe 2H-azirine 1 acts as an effective radical acceptor for secondary and tertiary alkyl iodides mediated by triethylborane. The addition proceeds with high regio- and diastereo-selectivity.