Solvolysis of specifically C-6 deuterated 7-halonorbornyl brosylates; stereoselectivity of proton loss for "E1-like" 1,3-elimination in locked bicyclo[2.2.1]heptyl Systems
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abstract
We have solvolyzed the syn-7-chloro-endo-6-d, anti-7-chloro-endo-6-d, syn-7-chloro-exo,exo-5,6-d2, anti-7-chloro-exo,exo-5,6-d2, syn-7-bromo-endo-6-d, and anti-7-bromo-endo-6-d norbornyl brosylates 1c, 2c, 1d, 2d, 1e, and 2e in 80:20 ethanol–water buffered with NaOAc, isolated the 3-halonortricyclenes, the products of 1,3-elimination, and assayed for deuterium mass spectrometrically. Analysis of the deuterium-loss data established that there is a 10:1 to 15:1 preference for loss of an endo-6-proton for formation of the 7-halonortricyclenes from the 7-halonorbornyl cations. The isotope effects for "E1-like" 1,3-elimination are 1.78, 1.71, 1.53, and 1.52 for 1c, 2c, 1e, and 2e, respectively. That there is an increase in the degree of 1,3-elimination in the solvolysis of anti-7-chloro-exo-2-norbornyl brosylate-exo-3-d (3) relative to the non-deuterated brosylate indicates that the destabilizing effect of the β-deuterium at C-3 leads to an increase in the degree of 1,3-elimination from C-6.
