Strain-Release Driven Annulations of Bicyclo[1.1.0]butanes and Ring-Opening of Donor-Acceptor Cyclopropanes

Abstract

The concept of strain release has long captivated chemists, particularly in the context of highly strained molecular frameworks such as bicyclo[1.1.0]butanes (BCBs), which possess a remarkable strain energy of 63.9 kcal/mol. Owing to the unique features, BCBs have emerged as versatile building blocks for the construction of bicyclic architectures that function as bioisosteres of aromatic rings. In this context, we have developed the Lewis acid-catalyzed (3+3) annulation of isatogens with BCBs, providing efficient access to bicyclo[3.1.1]heptane frameworks. Moreover, we have demonstrated the Lewis acid-catalyzed (4+3) annulation of para-quinonemethides with BCBs, enabling the synthesis of bicyclo[4.1.1]octane derivatives. Additionally, HFIP-mediated (3+3) and (3+2) annulations of BCBs with differently substituted indolyl alcohols have also been achieved, where HFIP simultaneously activates BCB and indolyl alcohols thus expanding the synthetic utility of this strained carbocycle. In another phase of work, we have disclosed the benzotriazole-triggered 1,3-aminohalogenation and 3,1-carboamination of donor-acceptor cyclopropanes under Lewis acid catalysis