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 bicyclo3.3.1]-1(2)-nonene (1) , bicyclo4.2.1]-1(8)-nonene (2) , and bicyclo4.2.1]-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-bicyclo3.3.1]nonane (4) and 1-bromobicyclo4.2.1]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 bicyclo4.2.1]nonenes 2 and 3 is similar to that in trans-cyclooctene (8-9 kcal/mol).