Thermal and Photochemical Reactions of 1,2-Annelated Barrelenes and Hydrobarrelenes in the presence of transition-metal carbonyls

The [Co2(CO)8]‐mediated retro‐Diels‐Alder reaction of the annelated barrelenes 1 afforded the 1H‐indol‐2(3H)‐one derivatives 3 (Scheme 1), while the hydrobarrelene 4a, under the same conditions, was converted to the anilide 6 (Scheme 2); 4b remained unaffected. The direct irradiation of 1 led to the annelated cyclooctatetraenes 7 (Scheme 3). On irradiation in the presence of excess of [Fe(CO)5], 1a, 1b, and 4a gave the tricarbonyliron complexes 8, 9, and 11, respectively (Schemes 3 and 4); under these conditions, 4b was inert.