Water-in-oil microemulsions as microreactors to control the regioselectivity in the photocycloaddition of 9-substituted anthracenes

The photocycloaddition of five 9-substituted anthracenes [AnCH2N+(CH3)3Br− (1), AnCH2COONa (2), AnCH2OH (3), AnCOCH3 (4), AnCH3 (5), An=9-anthryl] incorporated in water-in-oil microemulsions prepared from sodium bis(2-ethylhexyl) sulfosuccinate (AOT), methylene chloride and water has been investigated. While irradiation of the above substrates in methylene chloride, and 5 in the microemulsions also, mainly gave rise to their head-to-tail (h-t) photocyclomers, photoirradiation of the samples of 1–4 incorporated in the microemulsions almost exclusively yielded the head-to-head (h-h) photocyclomers. These observations were interpreted in terms of the preorientation of the substrate molecules at the interface of the water pool in the microemulsions.