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

The [Co 2 (CO) 8 ]‐mediated retro ‐ Diels ‐ Alder reaction of the annelated barrelenes 1 afforded the 1 H ‐indol‐2(3 H )‐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.