Electrophilic Additions to Strained Bridgehead Olefins. Estimation of Strain by Comparison with the Solvolysis of Bridgehead Bromides

The addition of water, acetic acid, and hydrogen bromide to the strained bridge‐head olefins bicyclo[3.3.1]‐1(2)‐nonene (1) , bicyclo[4.2.1]‐1(8)‐nonene (2) , and bicyclo[4.2.1]‐1(2)‐nonene (3) gives exclusively the bridgehead alcohols, acetates, and bromides, respectively. The reaction rate constants for the addition of acetic acid to the bridgehead olefins 1,2 and 3 , and the solvolysis rates for the related 1‐bromo‐bicyclo[3.3.1]nonane (4) and 1‐bromobicyclo[4.2.1]nonane (5) were measured. A comparison of the activation enthalpies of these two reactions gives an estimate of relative strain of the bridgehead double bond. The strain in the bicyclo[4.2.1]nonenes 2 and 3 is similar to that in trans ‐cyclooctene (8‐9 kcal/mol).