Formation of Bicyclic Skeletons by Aerobic, Manganese‐Mediated Cyclization of β‐Oxoesters

Bicyclic perhydro‐pentalene, ‐indene, and ‐azulene, as well as decaline skeletons were accessed by aerobic manganese(III)‐mediated radical cyclizations of cyclic β‐oxoesters with five‐, six‐, and seven‐membered rings and ω‐alkenyl‐ω‐phenyl C 4 –C 6 side chains in the β′‐position. After treatment of the intermediately formed peroxides with acetyl chloride and pyridine, Kornblum–DeLaMare fragmentation furnished the racemic bicyclic compounds with a 1,4‐dicarbonyl structural motif. In five out of eight cases investigated, the cyclization reactions were successful with 56%–72% yields. Diastereoisomers could be separated in most cases and their relative configuration established by X‐ray single crystal analysis, either directly or after derivatization with an aryl hydrazine. In the case of the pentalene and indane skeletons, conversion of their 1,4‐dicarbonyl motif with seven aryl hydrazines gave a pyridazine ring system with 62%–96% yields. Products are pentaleno[1,6‐ cd ]pyridazines or cyclopenta[ de ]cinnolines. A compound with a para ‐bromophenyl residue could be further derivatized in either a Suzuki cross‐coupling (84% yield) or a Heck reaction (88% yield).