The search for aliphatic nitrenium ions from solvolysis of N-2,2,6,6-tetramethylpiperidinyl p-nitrobenzoate

The N-4-nitrobenzoate of 1-hydroxy-2,2,6,6-tetramethylpiperidine undergoes solvolysis in methanol, trifluoroethanol, and hexafluoroisopropanol forming salts of 2,2,6,6-tetramethylpiperidine (4) and the rearranged iminium ion 19 which yields 2,2-dimethylpyrrolidine (26) on hydrolysis. In trifluoroacetic acid only the rearranged iminium ion 19b which forms 26 is observed, and the formation of this product is interpreted as involving ionization with rearrangement through an incipient nitrenium ion. The N-toluenesulfonate ester of 1-hydroxy-2,2,6,6-tetramethylpiperidine 24 was prepared as an unstable solid from 4-toluenesulfonyl chloride and N-hydroxy-2,2,6,6-tetramethylpiperidine, but upon chromatography rearranged to the cleavage product N-4-toluenesulfonyl-2,2-dimethylpyrrolidine(25).