Synthesis of spiropyrans: H-abstractions in 3-cycloalkenyloxybenzopyrans

• Satish C. Gupta,
• Mandeep Thakur,
• Somesh Sharma,
• Urmila Berar,
• Surinder Berar and
• Ramesh C. Kamboj

Beilstein J. Org. Chem. 2007, 3, No. 14, doi:10.1186/1860-5397-3-14

• ), followed by 1,5-H migration in 8a. [21] The spiropyrans 6 (R = H) bearing cyclopropanes are the secondary photoproducts formed as a result of the further reorganization of 5 (R = H), through a ring contraction-ring expansion mechanism. [22][23] The formation of acetylcyclopropane compound 7 (R = CH3) from

• that of the formation of 5 (R = CH3) from 2 (R = CH3). Regarding the stereochemical disposition of H-11b and H-3a in 5, both of them are cis placed (J = 9.6–9.9 Hz, Ø = 19.2°); in photoproducts bearing cyclopropanes [21]6 (R = H) or 7 (R = CH3), H-1 is trans to H-2 and H-3 (J1,2 = 4.8 Hz, J1,3 = 3.6 Hz