Evidence for symmetrical bridging in methylated 7-norbornenyl cations

Synthesis and solvolysis of derivatives of 7-methyl-7-hydroxynorbornane and the epimeric 7-methyl-7-hydroxynorbornenes

“…3.0 X 105 R^-OTs 3.7 X 10"4 « 1.8 X 1010 2.80 X 10°1.00 X 10" 7.6 X 103 22 R OPNB 1.01 X [10][11] 4.44 X 10-10 4.4 X 101 4.15 X 10-" d 4.13 X 10"4 d 1.0 X 10= d <* Calculated from the rate of the corresponding brosylate3 at 25°, assuming a brosylate: tosylate ratio of 2.90; ref 7. 6 Reference 9.…”

“…nzzíz-Hydroxy-syzj-7-methylnorbornene p-Nitrobenzoate (10). A solution of 1.50 g (12.1 mmol) of the anti alcohol, 7, in 25 ml of dry pyridine was cooled to 0°in an ice bath before the addition of 2.47 g (13.3 mmol) of p-nitrobenzoyl chloride.…”

“…This latter hypothesis has been substantiated solvolytically by Gassman and Patton,5 and more recently by nmr spectroscopic measurements on the 7-norbornenyl cation. 10 In order to obtain a more detailed insight into the mechanistic details of the formation of these ions, we decided to synthesize and solvolyze the appropriate 7-methylated derivatives. Starting with norbornen-7-one (6),11 we prepared a mixture of 7 and 8 via the addition of methyllithium as reported by Erman.12 Reduction of the mixture over palladium on carbon gave the saturated tertiary alcohol, 9. In view of the anticipated extreme reactivity of the tosylate of 7, no attempt was made to prepare this derivative.…”

The Realities of Extended Homoaromaticity

“…For example, H-6 and H-7 have experienced a substantial upfield shift (1.04ppm) 112 relative to (70) (this is 45 % as large as that observed in (66)). The bridge protons at C-8 likewise appear upfield [60% as large as that in (66)] while H-3 has moved downfield by 1.lOppm.…”

“…In this connection, Trimitsis and Tuncay have recently compared the rate of base-catalyzed hydrogen-deuterium exchange at C-4 in diene (70) with that of its dihydro derivative (71)['0'1. The kinetic imbalance was observed to be only 3.3 (compare k (65)/k(dihydro-(65)) = 1 04.5)[941 and both rate constants were closely related to that of the acyclic analog 1,3-diphenylpropene where no bishomoaromatic delocalization can develop.…”