Browsing by Author "Lopes, Marta"
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- Reacções de nitroso - e azo-vinilfosfonatos com alquenos e heterociclos ricos em electrõesPublication . Lopes, Marta; Lemos, A.Na presença de base, oximas e t-butoxicarbonilhidrazonas de halogenoacetilfosfonatos são convertidas “in situ” nos correspondentes nitroso- e azo-vinilfosfonatos. Estes são interceptados por alquenos e heterociclos ricos em electrões, em reacções Diels-Alder de procura electrónica inversa, produzindo oxazinas, piridazinas e aductos de cadeia aberta, com rendimentos razoáveis e boa selectividade. Os produtos (138) e (155) foram obtidos via reacção de eliminação-adição. Uma vez que, a redução da ligação C=N permite o acesso a α-aminofosfonatos que por hidrólise produzem ácidos α-aminofosfónicos, a metodologia usada neste trabalho, poderá ser interpretada como uma nova via sintética para obter este tipo de compostos.
- Reactions of Azovinylphosphonates with Nucleophilic Alkenes and Heterocycles: synthesis of Tetrahydropyridazine-3-phosphonate and 2-Substituted-1-hydrazonoethylphosphonate derivativesPublication . Lemos, A.; Lopes, MartaTransient azovinylphosphonates, generated in situ by base induced dehydrohalogenation of the corresponding 2-bromo- and 2-chloro-acetylphosphonate- tertbutoxycarbonyl hydrazones are intercepted by electron rich alkenes and heterocycles in hetero Diels-Alder reactions, producing tetrahydopyridazine-3-phosphonates or open chain α-hydrazono phosphonates.
- Reactions of azovinylphosphonates with nucleophilic alkenes and heterocycles: synthesis of Tetrahydropyridazine-3-phosphonate and 2-Substituted-1-hydrazonoethylphosphonate derivativesPublication . Lemos, A.; Lopes, MartaTransient azovinylphosphonates, generated in situ by base induced dehydrohalogenation of the corresponding 2-bromo- and 2-chloro-acetylphosphonate- tertbutoxycarbonyl hydrazones are intercepted by electron rich alkenes and heterocycles in hetero Diels-Alder reactions, producing tetrahydopyridazine-3-phosphonates or open chain α-hydrazono phosphonates.
- Reactions of nitrosovinylphosphonates with electron-rich alkenes and heterocyclesPublication . Lemos, A.; Guimaraes, Emanuel; Lopes, MartaIn the presence of a base, chlorohydroxyiminophosphonates are converted in situ into the corresponding transient nitrosovinylphosphonates, which react as heterodienes with electron-rich alkenes and heterocycles producing oxazines and open-chain oximes in moderate yields and good selectivity. This approach may be regarded as a new strategy for the synthesis of precursors of α-amino phosphonic acids.