Access to functionalized bicyclo[4,3,0]nonenes via palladium-catalyzed oxidative cyclization of 2-allylcyclohexyl oximes.

A new palladium-catalyzed oxidative cyclization process leading to the functionalized bicyclo[4,3,0]nonenes is serendipitously discovered during attempts to form aza-heterocycle by the amino-Heck reaction of trans-2-vinylclohexyl phosphinyloxime. Under the influence of Pd(dba)2/Et3N/1:1 N2-O2 (1:1, v/v) (Method A) or Pd(OAc)2/Et3N/O2 (Method B), the reactions afford the substituted cis-1-hydroxyl-8-formyl-bicyclo[4,3,0]non-8(9)-enes or bicycle[4,3,0]non-1(9)-en-8-ones in varying yields with the incorporation of molecular oxygen into the structures. The 5,6-bicyclic scaffold of these products is presumably derived from tandem double intramolecular cyclization followed by the ring-opening of an aza-palladium(II) tricyclic intermediate.