Generation and Trapping Reactions of 1-tert-Butoxycarbonyl-3,4-didehydro-1H-pyrrole.
3,4-Bis(trimethylsilyl)-1H-pyrrole (5) was employed as a key precursor to generate a highly strained and reactive five-membered cyclic cumulene, namely 1-tert-butoxycarbonyl-3,4-didehydro-1H-pyrrole (4). The transient existence of 4 at room temperature was confirmed by trapping reactions with furan, acrylonitrile, and benzene, affording cycloadducts 13-15. The choice of the electron-withdrawing tert-butoxycarbonyl group as the N-substituent was essential because it was able to adjust the electron density of 11a and 11b. As a result, monoiodonium triflates 12a and 12b were obtained, respectively. On the contrary, N-tert-butyl-3,4-bis(trimethylsilyl)-1H-pyrrole (9) led instead to the bisiodonium triflate 10 upon treatment with the Zefirov reagent.
Liu
Jian-Hui
JH
Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong.
Chan
Ho-Wai
HW
Xue
Feng
F
Wang
Qi-Guang
QG
Mak
Thomas C. W.
TC
Wong
Henry N. C.
HN