title: Variable strategy toward carbasugars and relatives. 5.(1) Focus on preparation of chiral nonracemic medium-sized carbocycles.
abstract: The feasibility of 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 gamma-substituted dihydro-5H-furan-2-one and pyrrolidin-2-one aldehydes (9, 16, ent-16, and 22) driven by the TBSOTf/Pr(i)(2)EtN Lewis acid-Lewis base couple was shown to be a practical, diastereoselective maneuver to forge the densely functionalized, medium-sized core carbocycles.
authors.affiliation: Istituto di Chimica Biomolecolare del CNR, Sezione di Sassari, Traversa La Crucca 3, Regione Baldinca, I-07040 Li Punti, Sassari, Italy.
authors.forename: Gloria
authors.initials: G
authors.lastname: Rassu
authors.forename: Luciana
authors.initials: L
authors.lastname: Auzzas
authors.forename: Luigi
authors.initials: L
authors.lastname: Pinna
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Zambrano
authors.forename: Franca
authors.initials: F
authors.lastname: Zanardi
authors.forename: Lucia
authors.initials: L
authors.lastname: Battistini
authors.forename: Enrico
authors.initials: E
authors.lastname: Gaetani
authors.forename: Claudio
authors.initials: C
authors.lastname: Curti
authors.forename: Giovanni
authors.initials: G
authors.lastname: Casiraghi