On the electronic effects of OH groups. Synthesis and investigation of tetrahydroxylated azabicycloheptanes
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Two stereoisomeric 2,3,5,6-tetrahydroxyazabicyclo[2.2.1]heptanes were synthesised and their base strengths determined. The 2,3,5,6-exo-isomer 1 and the 2,3-exo-5,6-endo-isomer 2 were prepared from the Diels-Alder adduct of Boc-pyrrole and tosylacetylene by a route involving osmium catalyzed dihydroxylation and protection, tosyl group reduction and repeated dihydroxylation. Deprotection gave 1, while 2 was obtained by conversion of the diol into the ditriflate, followed by nucleophilic inversion with KNO(2) and deprotection. Synthesis of the 2,3,5,6-endo-isomer by a similar strategy was attempted but failed. The pK(a) of 1 and 2 was determined to be 7.0 and 6.4 respectively. This means that the change in base strength as a result of stereoisomerism of an OH is smaller in the [2.2.1]-azabicyclic system than in the piperidines. This is explained by a difference in charge-dipole interactions in the two systems.
Originalsprog | Engelsk |
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Tidsskrift | Organic & Biomolecular Chemistry |
Vol/bind | 3 |
Udgave nummer | 8 |
Sider (fra-til) | 1514-1519 |
Antal sider | 6 |
ISSN | 1477-0520 |
DOI | |
Status | Udgivet - 2005 |
Eksternt udgivet | Ja |
ID: 109745252