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1. Ahmad, Anees. Exploring the iodine(III)-mediated ring contraction: new substrates, novel conditions and asymmetric reactions.

Degree: PhD, Química, 2015, University of São Paulo

In the first section this thesis includes the reactivity of various oxygen-containing benzofused cyclic alkenes with HTIB (Hydroxy(tosyloxy)iodobenzene). Instead of getting ring contraction products, 2H-chromene resulted in 4H-chromenes together with trans-addition products. Only cis-addition products were isolated from 4-methyl-2H-chromene. Ring contraction was observed in dihydrobenzoxepines and 2,2-dimethyl-2H-chromenes giving functionalized chromanes and benzofurans, respectively. In the second part, the ring contraction of 1,2-dihydronaphthalenes using HTIB was expanded to substrates bearing oxygen and nitrogen substituents in the aromatic ring. The N-protecting groups Fmoc and Bz are stable under the reaction conditions giving indanes in 64-77% yield. The Ts-protected substrate gave only addition products. Acetoxy and benzoyloxy alkenes afforded indanes in 60-71% yield. A new and efficient method for the oxidative rearrangement (ring contraction and expansion) of alkenes using in situ generated iodine(III) is described in the third section. The protocol uses inexpensive and stable chemicals (PhI, mCPBA and TsOH) furnishing rearrangement products in yields comparable to those obtained using commercially available iodine(III). Additionally, a new route for the one step transformation of 4-methyl-1,2-dihydronaphthalene into 1-methyl-2-tetralone using mCPBA and TsOH was developed. In the last section is presented the reactivity of chiral iodine(III) with 1,2-dihydronaphthalenes. The hypervalent iodine species is generated in situ from chiral aryl iodide, which is prepared in one high yield step from inexpensive starting materials. Protected (Ac, Bz and Fmoc) amine alkenes gave indanes in 60-75% and 58-64% ee. In the same way, oxygenated substrates afforded acetal in 41-61% yield and 54-78% ee. Ring contraction products were obtained in 77-88% yield and 34-40% ee when 1-methyl and aryl substituted alkenes were utilized.

A primeira parte desta tese inclui a reatividade de vários alquenos benzofundidos cíclicos contendo oxigênio com HTIB (Hidróxi(tosilóxi)iodobenzeno). Em vez de obter os produtos de contração de anel, 2H-cromeno resultou em 4H-cromenos, juntamente com produtos trans-adição. Apenas produtos de adição de cis foram isolados a partir de 4-metil-2H-cromeno. Contração do anel foi observada em di-hidrobenzoxepinas e 2,2-dimetil-2H-cromenos dando cromanos funcionalizados e benzofuranos, respectivamente. Na segunda parte, a contração de anel de 1,2-di-hidronaftalenos usando HTIB foi expandida para substratos contendo substituintes de oxigênio e de nitrogênio no anel aromático. Os grupos N-protetores Fmoc e Bz são estáveis sob as condições de reação fornecendo indanos em 64-77% de rendimento. O substrato protegido com Ts deu apenas os produtos de adição. Acetóxi e benzoilóxi alquenos geraram indanos em 60-71% de rendimento. Um método novo e eficiente para o rearranjo oxidativo (contração e expansão do anel) de alquenos utilizando iodo(III) gerado in situ é descrito na terceira parte. O protocolo utiliza…

Advisors/Committee Members: Silva Junior, Luiz Fernando da.

Subjects/Keywords: Benzofuranos; Benzofurans; Chiral iodine(III); Chromanes; Contração de anel; Cromanos; Hypervalent iodine; Indane; Indano; Iodo hipervalente; Iodo quiral (III); Organic synthesis; Oxidative rearrangement; Rearranjo oxidativo; Ring contraction; Síntese orgânica

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APA (6th Edition):

Ahmad, A. (2015). Exploring the iodine(III)-mediated ring contraction: new substrates, novel conditions and asymmetric reactions. (Doctoral Dissertation). University of São Paulo. Retrieved from http://www.teses.usp.br/teses/disponiveis/46/46136/tde-29092015-145020/ ;

Chicago Manual of Style (16th Edition):

Ahmad, Anees. “Exploring the iodine(III)-mediated ring contraction: new substrates, novel conditions and asymmetric reactions.” 2015. Doctoral Dissertation, University of São Paulo. Accessed July 03, 2020. http://www.teses.usp.br/teses/disponiveis/46/46136/tde-29092015-145020/ ;.

MLA Handbook (7th Edition):

Ahmad, Anees. “Exploring the iodine(III)-mediated ring contraction: new substrates, novel conditions and asymmetric reactions.” 2015. Web. 03 Jul 2020.

Vancouver:

Ahmad A. Exploring the iodine(III)-mediated ring contraction: new substrates, novel conditions and asymmetric reactions. [Internet] [Doctoral dissertation]. University of São Paulo; 2015. [cited 2020 Jul 03]. Available from: http://www.teses.usp.br/teses/disponiveis/46/46136/tde-29092015-145020/ ;.

Council of Science Editors:

Ahmad A. Exploring the iodine(III)-mediated ring contraction: new substrates, novel conditions and asymmetric reactions. [Doctoral Dissertation]. University of São Paulo; 2015. Available from: http://www.teses.usp.br/teses/disponiveis/46/46136/tde-29092015-145020/ ;

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