Intramolecular [5+2] photocycloaddition of maleimides; Perhydroazaazulene ring system

James Baker ([email protected]),
A contribution from the Booker-Milburn Group, Bristol

Chemicals Used
3,4-Dimethyl-1-pent-4-enyl-pyrrole-2,5-dione [SyntheticPage 4] Acetonitrile

Procedure
A solution of 3,4-Dimethyl-1-pent-4-enyl-pyrrole-2,5-dione (0.250g, 1.3mmol) in Acetonitrile (125ml) was degassed with Nitrogen for 15 min, then irradiated in a pyrex vessel using a mediuim pressure mercury lamp for 2.5h. The solvent was removed, then the crude product was purified by column chromatography (100% EtOAc) to leave a white crystalline solid (247mg, 99%).

Author's Comments
This [5+2] photocycloaddition reaction is general for a number of alkenyl substituted maleimide derivatives and gives the bicyclic azepines in high yields. More substituted acyclic and cyclic alkene side chains can be used, leading to cycloadducts with high levels of stereoselectivity. Use of the unsubstituted, parent maleimide leads to side reactions mainly associated with photodimerisation.

Data
m.p. 81^o C; ¹H-NMR (300MHz, CDCl₃) 4.29-4.18 (m, 1H), 3.69-3.46 (m, 2H), 2.72 (dd, J = 18.8, 11.4 Hz, 1H), 2.64 (dd, J = 18.8, 3.7Hz, 1H), 2.24-2.10 (m, 1H), 2.02(s, 3H), 1.96-1.84 (m, 2H), 1.89 (s,3H), 1.75-1.66 (m, 1H).

Lead Reference
Eur.J.Org.Chem.2001, 1473-1482

Other References

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