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Variable Strategy towards Carbasugars and Relatives. 5. Focus on Preparation of Chiral Nonracemic Medium-Sized Carbocycles (Articolo in rivista)

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Variable Strategy towards Carbasugars and Relatives. 5. Focus on Preparation of Chiral Nonracemic Medium-Sized Carbocycles (Articolo in rivista) (literal)

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Rassu G., Auzzas L., Pinna L., Zambrano V., Zanardi F., battistini L., Gaetani E., Curti C., Casiraghi G. (2003)
Variable Strategy towards Carbasugars and Relatives. 5. Focus on Preparation of Chiral Nonracemic Medium-Sized Carbocycles
in Journal of organic chemistry
(literal)

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Rassu G., Auzzas L., Pinna L., Zambrano V., Zanardi F., battistini L., Gaetani E., Curti C., Casiraghi G. (literal)

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La rivista è al primo posto per totale di citazioni (63233 citazioni totali) nella categoria ISI-Chimica Organica. La stessa è al terzo posto tra le 12 riviste più richieste dell'area chimica (CAS Science Spotlight) (literal)

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An adaptable, ex chiral-pool synthesis of scarcely represented medium-sized carbasugar compounds has been established. Key features of the unified synthetic scheme include the stereocontrolled construction of the multifunctional carbon framework of the targeted molecules via a vinylogous Mukaiyama-aldol reaction and the assembly of the medium-sized cyclic domain via diastereoselective intramolecular silylative aldolization. Installation of the exocyclic hydroxymethyl or carboxylic groups was eventually achieved by simple reductive or hydrolytic fragmentations. As demonstrated by the preparation of chiral nonracemic carbaheptocycloseptanoses 1, 2, 3, ent-2, and ent-3 and carbaoctocyclooctanose 4, our methodology proved feasible, stereocontrolled, and synthetically efficient, with overall yields ranging from 21 to 30% for 8-12 step sequences. The successful exploitation of our silylative aldol annulation to implement seven- and eight-membered ring systems presents itself as a brilliant solution to the challenging task of assembling these expanded carbocyclic motifs establishing the basis for future applications. (literal)

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Istituto di Chimica Biomolecolare del CNR, Sezione di Sassari, Traversa La Crucca 3, Regione Baldinca, I-07040 Li Punti, Sassari, Italy, Dipartimento di Chimica, Università di Sassari, Via Vienna 2, I-07100 Sassari, Italy, Dipartimento Farmaceutico, Università di Parma, Parco Area delle Scienze 27A, I-43100 Parma, Italy (literal)

Titolo

Variable Strategy towards Carbasugars and Relatives. 5. Focus on Preparation of Chiral Nonracemic Medium-Sized Carbocycles (literal)

Abstract

The feasibility of the sequential vinylogous aldol (intermolecular)/silylative aldol (intramolecular) addition reactions involving furan- and pyrrole-based dienoxysilanes, 6 and 12, in the synthesis of carbasugar frameworks is illustrated by the preparation of the scantily investigated carbaseptanose and carbaoctanose representatives of this class of compounds. The target compounds, 1, 2, 3, ent-2, ent-3, and 4, were obtained from readily available carbohydrate precursors (5 and 19) in yields of 21-30% over 8-12 steps. The irreversible silylative ring-closing aldolisation of ×-substituted dihydro-5H-furan-2-one and pyrrolidin-2-one aldehydes (9, 16, ent-16, and 22) driven by the TBSOTf/Pri2EtN Lewis acid-Lewis base couple was shown to be a practical, diastereoselective manoeuvre to forge the densely functionalised, medium-sized core carbocycles. (literal)

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