ipso-vs. tele-Nucleophilic substitution by piperidine on isocolchicides and colchicides bearing an α-leaving group

Product studies of the reactions of piperidine with colchicides carrying a C-10 nucleofugic group show that only ipso substitution occurs. For isocolchicides carrying an X nucleofugic group at C-9, similar behaviour was observed for X = F, OTs or OMe, while for X = SMe, SOMe or Cl tele substitution (at C-11) competes with ipso substitution. These results together with the observation that the reaction rates for the two series are similar, may be useful in guiding the refunctionalization of similar compounds.