Nortricyclyl−Norbornenyl Cation System Accessed by Carbene Fragmentation

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