Nortricyclyl−Norbornenyl Cation System Accessed by Carbene Fragmentation
2004-05-28T00:00:00Z (GMT) by
Fragmentation of nortricyclyloxychlorocarbene <b>5 </b>in pentane occurs by an S<sub>N</sub>i-like process which yields nortricyclyl chloride <b>3g</b>. In more polar solvents, fragmentation leads to nortricyclyl cation chloride anion pairs (<b>9</b>) that give mainly <b>3g</b>, accompanied by ∼10% of <i>exo</i>-2-norbornenyl chloride <b>4g</b>. From <i>exo</i>-2-norbornenyloxychlorocarbene <b>6</b> in hydrocarbon solvents, “S<sub>N</sub>i” reactions lead mainly to <i>exo-</i> (<b>4g</b>) and <i>endo-</i>2-chloro-5-norbornenes (<b>4g</b>‘). Leakage to ion pairs adds ∼16% of nortricyclyl chloride <b>3g</b>. In more polar solvents, the main product remains chloride <b>4g</b>, but increasing quantities of <b>3g</b> appear due to enhanced participation of ion pairs. Fragmentations of <b>5</b> and <b>6</b> in MeOH afford chlorides <b>3g</b> and <b>4g</b> as well as the corresponding methyl ethers <b>3b</b> and <b>4b</b>. Nortricyclyl cation and norbornenyl cation chloride anion pairs and methanol-solvated nortricyclyl cations are invoked to rationalize the results.
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