Allylic vs. Vinylic Deprotonation Reactions of Cyclic Vinyl Ethers. 7-Lithio-2,3,4,5-tetrahydrooxepin: Synthesis and Carbon-13 Nuclear Magnetic Resonance Spectrum

Article abstract of DOI:10.1021/jo00137a013

2,3,4,5-Tetrahydrooxepin treated with either n-butyllithium or tert-butyllithium affords 7-lithio-2,3,4,5-tetrahydrooxepin.The question of allylic vs. vinylic deprotonation of cyclic vinyl ethers was examined by varying ring size and degree of unsaturation.Carbon-13 spectral data for the anions obtained from 2,5-dihydrofuran, 2,3-dihydrooxepin, and 2,3,4,5-tetrahydrooxepin are reported.In contrast to 2,3,4,5-tetrahydrooxepin, 2,3-dihydrooxepin undergoes allylic deprotonation, possibly as a result of a slightly larger C-C=C bond angle in the dihydrooxepin as compared to that of the tetrahydrooxepin.