3721-18-4Relevant academic research and scientific papers
Endo entry to the nortricyclyl-norbornenyl cation system: Stereochemistry in the fragmentation of endo-5-norbornenyl-2-oxychlorocarbene
Moss, Robert A.,Fu, Xiaolin,Sauers, Ronald R.,Wipf, Peter
, p. 8454 - 8460 (2007/10/03)
Fragmentation of (S)-endo-5-norbornenyl-2-oxychlorocarbene [(S)-8] in cyclohexane-d12 gives ～20% (S)-endo-2-chloro-5-norbornene [(S)-7] with ～50% ee, 65-70% (R)-exo-2-chloro-5-norbornene [(R)-4] with >95% ee, and ～12% (R)-3-nortricyclyl chloride [(R)-5] with ～22% ee. (Analogous stereochemical results were also obtained starting with the enantiomeric carbene (R)-8.) The (S)-8 to (S)-7 and (S)-8 to (R)-4 conversions are ascribed mainly to retention and inversion SNi transition states, respectively. These have been located by computational methods and are nearly isoenergetic. In more polar solvents (CDCl3 and CD3CN), the fragmentation of (S)-8 increasingly occurs via competitive ion pair pathways in which steroselectivity is diminished, and escape to the norbornenyl-nortricyclyl cation directs the products away from endo-2-chloro-5-norbornene toward exo-chloride 4 and nortricyclyl chloride 5.
Nortricyclyl-norbornenyl cation system accessed by carbene fragmentation
Moss, Robert A.,Ma, Yan,Sauers, Ronald R.,Madni, Mahvash
, p. 3628 - 3634 (2007/10/03)
Fragmentation of nortricyclyloxychlorocarbene 5 in pentane occurs by an SNi-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, "SNi" 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.
