Photodimerization of Coumarins in Micelles: Limitations of Alignment Effect

Organized media such as micelles have shown great promise in achieving regio- and stereoselectivity in photochemical cycloaddition reactions as has been shown by recent reports. 7-Alkoxy- and 4-methyl-7-alkoxycoumarins dimerize in organic solvents to give the syn head-tail dimer. However, dimerization of these coumarins in SDS and CTAB micelles did not show any reversal in this trend. The results probably indicate that the micellar orientational effect is most effective only in those systems where the forces that control regiochemistry are weaker than hydrophobic association energies.