Syn to anti isomerization and degradation of phosphines of the 7-phosphanorbornene system by action of methanol

$\text{Syn}$-Substituted phosphines of the 7-phosphanorbornene system form unstable phosphorane adducts with methanol that either fragment by retro-McCormack cycloaddition or undergo polytopal rearrangement and loss of methanol to give the first examples of $\text{anti}$ phosphines.