Stable-Ion NMR Spectroscopy and GIAO-DFT Study of Carbocations Derived from Multibridged [3(n)]Cyclophanes

作者：Laali Kenneth K^*; Okazaki Takao; Kitagawa Toshikazu; Shinmyozu Teruo

来源：European Journal of Organic Chemistry, 2009, 2009(26): 4451-4457.

DOI：10.1002/ejoc.200900479

• Cyclophanes
• Protonation
• Carbocations
• Donor-accepter systems
• Superacidic systems

Mono- and diprotonation of the tri-, tetra-, and pentabridged cyclophanes [3(3)](1,3,5)cyclophane (4), [3(4)](1,2,3,5)cyclophane (5), and [3(5)](1,2,3,4,5)cyclophane (6) were realized, and NMR spectroscopic studies of the resulting carbocations are reported. Unlike [2.2]paracyclophane and its fluorinated analogs that are protonated at a position ipso to the ethano-bridge, the monocations derived from 4, 5, and 6 are protonated at the unsubstituted ring positions. Protonation regioselectivity in the dications is pseudo-meta for 4 and 5 at unsubstituted ring positions, but for more-crowded 6 the second protonation occurs at a position that is ipso to the trimethylene bridge. Transarmular pi-pi interactions in the monocations are manifested in the observed proton deshielding in the unprotonated pi-deck. DFT and GIAO-DFT were employed to study the mono- and dications for comparison with the solution studies in superacids. GIAO-derived Delta NICS(1)(zz) data for the [3(n)]cyclophane monocations imply decreased aromaticity in the cofacial unprotonated arene, consistent with transannular donor-acceptor interactions.

• 出版日期2009-9