Surprising exocyclic regioselectivity in electrophilic additions to alkylidenecyclobutenes

Hillel Pizem, Ofer Sharon, Aryeh A. Frimer

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


The addition of peracid, bromine, TCNE and singlet oxygen to alkylidenecyclobutenes shows a strong regioselectivity - in some cases regiospecificity - for the exocyclic double bond. Depending on the reagent, the endocyclic double bond will only undergo reaction upon the addition of a second equivalent of reagent. In the case of the first three reagents, this exocyclic regioselectivity is rationalized by invoking the formation of the more stabilized carbocation intermediate or transition state. Regarding 1O2, where polar mechanisms are rare, we attribute this exocyclic regioselectivity to the improper alignment and, hence, lack of reactivity of the endocyclic allylic hydrogen.

Original languageEnglish
Pages (from-to)3199-3205
Number of pages7
Issue number16
StatePublished - 15 Apr 2002


  • Addition reactions
  • Cyclobutenes
  • Oxygen, singlet
  • Regioselection


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