Intramolecular Oxymercuration of Stereoisomeric Cyclohexyl-Belted Poly(spirotetrahydrofuranyl) Platforms

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• 作者：Leo A. Paquette ; David G. Bolin ; Marshall Stepanian ; Bruce M. Branan ; Uppuluri V. Mallavadhani ; Jinsung Tae ; Shawn W. E. Eisenberg ; and Robin D. Rogers
• 刊名：Journal of the American Chemical Society
• 出版年：1998
• 出版时间：November 18, 1998
• 年：1998
• 卷：120
• 期：45
• 页码：11603 - 11615
• 全文大小：564K
• 年卷期：v.120,no.45(November 18, 1998)
• ISSN：1520-5126

文摘

The four tetraspiro carbinols 28, 30, 41, and 43 and the three trispiro cyclohexenones 25, 38, and53 have been synthesized and individually subjected to intramolecular oxymercuration. The three-dimensionalstructures of all 10 products have been unequivocally established by X-ray crystallographic analysis. In sevenof these structures, the preferred solid-state conformation features an axially disposed C-Hg bond where themercury atom is internally chelated in a 1,3-diaxial relationship to at least one or, more often, two oxygencenters. An unusually strong preference has been observed for equatorial occupancy on the part of the C-Obonds. This bias can be attributed to the relief of torsional strain effects that arise when gauche CH₂- - -CH₂interactions are skirted. An important mechanistic distinction separates the kinetically preferred transmercuricyclization of the tetraspiro alcohols from the contrasting cis stereochemical ring closure exhibitedpredominantly by the unsaturated ketones. In the first instance, the approach of Hg²⁺ to the double bond isgoverned to a large extent by coordination to a proximal axially oriented ether oxygen. Where the ketones areconcerned, precoordination to the Lewis basic carbonyl oxygen presumably initiates spirocyclization in a fashioncontrolled by the conformational preference of the resident tetrahydrofuranyl subunits.