The present invention provides a method of preparing a compound of formula 6comprising:(a) reacting a compound of formula 1with a compound of formula 2to form a compound of formula 3wherein X of formula 2 is Cl or OH (b) treating the compound formula 3 with Lawessons reagent to form a compound of formula 4(c) reacting a compound of formula 4 with potassium ferricyanide to produce a compound of formula 5and(d) performing catalytic reduction of nitro group of the compound of formula 5 with palladium on charcoal to generate the compound of formula 6,wherein R1 of formulae 1-6 is H, C1-10 alkyl, C1-10 alkoxy or C1-10 haloalkyl, and R2 of formulae 1-6 is H or C1-10 alkyl.The present invention also provides a photodynamic therapy to a patient having at least one tumor comprising the steps of: administering a compound of formula 6 (wherein R1 and R2 are defined as the above) in a pharmaceutically acceptable carrier to the patient waiting for a sufficient time to allow the administered compound to be taken up by a target tissue having the at least one tumor and irradiating a region of the patient containing the target tissue wherein growth of the tumor is inhibited.
