Acetolysis of 4-homoadamantyl tosylate. Multiple degenerate rearrangements and mechanism
| Autor: | Satya P. Jindal, J. Eric Nordlander, John B. Hamilton, Robert R. Gruetzmacher, Felicia Ying-Hsiueh Wu |
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| Rok vydání: | 1976 |
| Předmět: | |
| Zdroj: | Journal of the American Chemical Society. 98:6658-6669 |
| ISSN: | 1520-5126 0002-7863 |
| Popis: | Buffered acetolysis of 4-homoadamantyl tosylate (6) at 40 0C produces 75% of 4-homoadamantyl aacetate (7) and 25% of 4-homoadamantene (8). It is shown by deuterium labeling that the substitution process is accompanied by full degener ate stereospecific Wagner-Meerwein equilibration of the 4-homoadamantyl cation, 1, together with its partial degenerate re arrangement by vicinal hydride shift. The nonstereoselectivity of the hydride migration and the absence of kinetic evidence for anchimeric assistance argue against a carbon-bridged structure for the intermediate carbenium ion, 1. The elimination reac tion, in contrast, is evidenced to involve preliminary Wagner-Meerwein equilibration but no appreciable hydride shift and is predominantly a syn El process. These and related results are interpreted as indicating that elimination takes place wholly from an initially formed Wagner-Meerwein pair of nonepimerizing intimate ion pairs, that irreversible dissociation of the lat ter precedes hydride migration, and that the formation of acetate takes place principally from solvent-separated ion pairs. The analysis of multiple degenerate rearrangements in solvolytic or stable carbocations has provided insight into a number of dynamic systems.2 In most of these a single type of rearrangement has been involved, usually a 1,2-carbon shift. Our attention has been directed to a system potentially de generate under two different rearrangement processes, whose analysis under solvolytic reaction offered the prospect of ex tensive mechanistic information. The 4-homoadamantyl (4- tricyclo(4.3.1.13'8)undecyl) cation, 1, is degenerate with respect both to Wagner-Meerwein rearrangement and to vicinal hy dride shift, the two processes being distinguishable on the basis of deuterium label transpositions, as illustrated for \-4-d. We |
| Databáze: | OpenAIRE |
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