A Substrate-Based Approach to Skeletal Diversity from Dicobalt Hexacarbonyl (C1)-Alkynyl Glycals by Exploiting Its Combined Ferrier-Nicholas Reactivity

• Published in: Chemistry : a European journal 2014-08, Vol.20 (33), p.10492-10502
• Main Authors: Lobo, Fernando, Gómez, Ana M., Miranda, Silvia, López, J. Cristóbal
• Format: Article
• Language: English
• Subjects: Alterations; Branched; Cations; Chemistry; Derivatives; Ferrier reaction; glycals; Hydroxyl groups; Nicholas reaction; Nucleophiles; Pathways; synthesis design; synthetic methods; Tetrahydrofuran
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201402149

Novel substrates that combine dicobalt hexacarbonyl propargyl (Nicholas) and pyranose‐derived allylic (Ferrier) cations have been generated by treatment of hexacarbonyldicobalt (C‐1)‐alkynyl glycals with BF3.Et2O. The study of these cations has resulted in the discovery of novel reaction pathways that have shown to be associated to the nature of O‐6 substituent in the starting alkynyl glycals. Accordingly, compounds resulting from ring expansion (oxepanes), ring contraction (tetrahydrofurans), or branched pyranoses, by incorporation of nucleophiles, can be obtained from 6‐O‐benzyl, 6‐hydroxy, or 6‐O‐silyl derivatives, respectively. The use of a 6‐O‐allyl alkynyl glycal led to a suitable funtionalized oxepane able to experience an intramolecular Pauson–Khand cyclization leading to a single tricyclic derivative. Skeletons out of the cupboard: Dicobalt hexacarbonyl (C1)‐alkynyl glycals, might give raise to ring‐expansion oxepanes, ring‐contraction tetrahydrofurans, or multibranched tetrahydropyrans, by subtle reactivity alterations induced by changes in the substitution of the primary hydroxyl group, upon treatment with BF3⋅Et2O (see scheme).