Azepines, photocycloaddition

The use of metal complexed heterocyclic polyenes in these cycloadditions has also proven useful, as both the 1,1-dioxythiepine and azepine derivatives 250 and 253 took part in [6 + 4]- and [6+ 2]-photocycloadditions, respectively, to afford good yields of the... 

Of the 5-membered heteroaromatic systems, pyrrole reacts most like benzene in alkyne photocycloaddition, giving a 3,4-disubstituted azepine by 2,3-cycloaddition followed by electrocyclic ring-opening fequation 73) . Azepines with a different substitution pattern have been made by therpial 2,5-addition of an alkyne to a pyrrole, followed by photochemical ring-closure and thermal ring-opening of the tetracyclic photoproduct (equation 74) . 

Ring contraction. The process is required to synthesize (+)-ferruginine based on a route starting from a chromium-promoted [6+2]photocycloaddition of azepines. The proper bridged heterobicyclic system evolves from a TTN oxidation. 

Scheme 4.14 Synthesis of tricyclic azepine by [5 + 2] photocycloaddition reaction of A -alkenyhnaleimide derivatives.

Kobayashi, K., Suzuki, M., and Suginome, H., Photoinduced molecular transformations. 128. Regioselective [2-1-2] photocycloaddition of 3-acetoxyquinolin-2(lH)-one with alkenes and formation of furo [2,3-c] quinolin-4(5fd)-ones, l-benzazocine-2,3-diones, and cyclopropa [d] benz [1] azepine-2,3-diones via a P-scission of cyclobutanoxyl radicals generated from the resulting [2-1-2] photoadducts, /. Org. Chem., 57, 599,1992. 

---