Alkynylcyclohexanol Chairs and Twist-Boats: Co<sub>2</sub>(CO)<sub>6</sub> as a Conformational Switch
作者:Nicole M. Deschamps、John H. Kaldis、Philippa E. Lock、James F. Britten、Michael J. McGlinchey
DOI:10.1021/jo0108820
日期:2001.12.1
Treatment of 1-[axial]-(trimethylsilylethynyl)cyclohexan-1-ol with dicobalt octacarbonyl results in a conformational ring flip such that the bulky dicobalt-alkyne cluster moiety now occupies the favored equatorial site. However, when a 4-tert-butyl substituent is present, the coordinated alkynyl group retains its original axial or equatorial position. Complexation of trans-[diaxial]-1,4-bis(triphenylsilylethynyl)cyclohexane-1,4-diol brings about a chair-to-chair conformational inversion such that both cluster fragments now occupy equatorial sites. In contrast, cis-1,4-bis(triphenylsilylethynyl)cyclohexane-1,4-diol reacts with CO2(CO)(8) to yield the twist-boat conformer in which the two axial hydroxy substituents exhibit intra-molecular hydrogen bonding. Likewise, the corresponding reaction of cis-1,4-bis(trimethylsilylethynyl)cyclohexane-1,4-diol with CO2(CO)(8) leads to a twist-boat, but in this case, the molecules are linked through inter-molecular hydrogen bonds. Eight of these cobalt clusters have been characterized by X-ray crystallography, and the potential use of twist-boats in synthesis is discussed.