Synthesis of Psoralen Analogues Based on Dibenzofuran by Ana M. A. G. Oliveira a ), M. Manuela M. Raposo a ), Ana. M. F. Oliveira- Campos a ) * , John Griffiths b ), and Antonio E. H. Machado c ) a ) Centro de Química, IBQF, Universidade do Minho, Campus de Gualtar, P-4710 Braga b ) Department of Colour Chemistry, University of Leeds, Leeds LS2 9JT, UK. c ) Universidade Federal de Uberlândia – Instituto de Química, Laboratório de Fotoquímica/GFQM, P.O. Box 593, Uberlândia, 38400-089, Minas Gerais, Brasil. Abstract. The syntheses of four novel psoralen derivatives, 6a-d, of the benzofurocoumarin (=benzofuro[1]benzopyranone) type containing an ester group are described. These compounds might be of interest in PUVA (psoralen long-wave ultraviolet radiation) therapy. The overall efficiency of the synthetic procedure is greatly limited by the low yields for the penultimate step, i.e. formylation of the dibenzofuranols 3a,c or protected dibenzofuranol 4d to the carboxaldehydes 5 (Scheme 4). However, the final stage to form the pyranone ring from 5a-d proceeds smoothly (Scheme 5). 1. Introduction.- Benzopsoralens, which may be considered as benzofuro-fused coumarin systems (=benzofuro[1]benzopyranone), have previously been synthesized and their biological propertieshave been studied [1] [2]. Introduction of a benzene ring fused to the furan moiety, or bulky or electron-withdrawing substituents at the pyranone ring have been proposed as potential ways to inhibit adduct formation with DNA [3]. In addition, Gia et al. [2] have shown that the introduction of an ester group into a benzopsoralen can provide derivatives, which are efficient photosensitizers of singlet oxygen. Recently, the photophysical properties of three such compounds have been investigated, and it was shown that two of them could 1