Ring-Strain Enabled Transannulation of N-Aryl Bicyclo[1.1.0]butane Carboxamides via Rhodium(II)Carbene Intermediate

Abstract The C–C bond cleavage is a fascinating area in synthetic organic chemistry, driven by ring-strain-enabled transformations. Here, we report the reactivity of the rhodium(II)-catalyzed, ring-strain-enabled N -aryl bicyclo[1.1.0]butane carboxamide in a transannulation reaction. The efficiency of this methodology demonstrates significant advances in metallocarbene chemistry, generating a novel class of acceptor type allyl carboxamide Rh(II)-carbene intermediate, notably without the need for coordinating groups or external ligands. The reactivity was systematically investigated using various substituted N -aryl bicyclo[1.1.0]butane-1-carboxamides, leading to impressively efficient synthesis of 3-allyl oxindoles via transannulation. [1,2]– H Migration is also shown via an in situ-generated Rh(II)-carbene intermediate. Furthermore, the broad synthetic utility of this method is a promising development, enabling the diversification of key functional groups and the access to structurally relevant intermediates and biologically active molecule precursors, including the CB2 agonist and Horsfiline. Control experiments and DFT calculations showed that the transformation proceeds via a Rh(II)-carbene intermediate.