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

The photocycloaddition of five 9-substituted anthracenes [AnCH(2)N(+)(CH3)(3)Br (1), AnCH(2)COONa (2), AnCH(2)OH (3), AnCOCH(3) (4), AnCH(3) (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. (C) 2002 Elsevier Science Ltd. All rights reserved.