Bicyclic carbonation rearrangements

• Main Author: Steel, P. J.
• Language: en
• Published: University of Canterbury. Chemistry 2013
• Online Access: http://hdl.handle.net/10092/8325

The ¹³C n.m.r. spectrum of the 2-phenylbicyclo[ 2,2,1]hept-2-yl cation (9) is examined and three of the seven skeletal carbons are reassigned. The temperature- dependence of this spectrum is discussed and the effects of substituents in the phenyl ring on cation stability and structure is examined. The reaction of alcohols (17a-d) with concentrated perchloric acid give dimers (25) and (26). The structures of (25d) and (26d) are determined by X-ray crystallography. Reaction of alcohols (28) with fluorosulphonic acid gives cations (30) which rearrange to (31) and (32). The mechanisms of these rearrangements and the structures of the cations are discussed. The n.m.r. spectra of the epimeric cations (36) and (39) are reported and the relative stability of these cations is discussed. The ¹³C n.m.r. spectra of alcohols (44a-d) and (45) are unambiguously assigned. At low temperatures alcohols (44) react with HSO₃F to give cations (16) whose ¹³C n.m.r. spectra provide evidence for the existence of C1-C6 σ-bond delocalisation. At higher temperatures rearrangement takes place to give cations (47a-d) and (50b) which in turn undergo ring opening to give cations (48). The cations generated from alcohols (58a-c) are investigated and a complex sequence of rearrangements involving six observable cations is deduced. The mechanisms and significance of these rearrangements are discussed. At low temperature alcohols (79a-c) similarly give cations (80) and (82). Reaction of alcohols (86) with HSO₃F at low temperatures give cations (63) whose ¹³C n.m.r. spectra are discussed. At higher temperatures these cations undergo an unusual rearrangement to give the tetracyclic compounds (89-91). Alcohol (103) produces the rearranged cation (105) while (104) gives the parent cation (106) which subsequently rearranges to (105). The cations produced from alcohol, (109) are also investigated. Mechanisms are proposed for all rearrangements and the relevance of the cations as model systems is discussed.