2,6-difluoro-4'-methoxybenzophenone was prepared by Friedel-Crafts reaction of 2,6-difluorobenzoyl chloride with anisole in carbon disulfide using aluminum chloride as catalyst. 4.8 grams (0.02 mole) of the benzophenone was converted to the propargyl alcohol using the conditions described in Example 1, Step 2. The crude propargyl alcohol was taken up in 200 milliliters of benzene and 3.0 grams (0.02 mole) of naphthol and 0.1 grams of p-toluene sulfonic acid catalyst was added to the benzene solution. After stirring for 1 hour, the reaction mixture was poured into an equal volume of 5 percent aqueous sodium hydroxide. The organic layer was separated and the benzene solvent removed on a rotary evaporator. The residue was chromatographed on silica using a 4:1 mixture of hexane:ethyl acetate as elutant. The photochromic fractions were collected and crystallized from n-propanol. 1.2 grams of product having a melting range of 122-124° C. was obtained. NMR analysis confirmed the product to be 3(2,6-difluorophenyl)-3(4-methoxyphenyl)-3H- naphtho[ 2,1-b]pyran.
