NOVEL MACROCYCLES FROM METAL-CATALYZED OXIDATIVE CYCLIZATIONS OF A,C-BILADIENE SALTS

From the metal-promoted oxidative cyclization of several 1,19-disubsti tuted a,c-biladiene dihydrobromide salts, a number of novel macrocycle s were prepared. For example, the cyclization of thyl)-2,3,7,8,12,13,1 7,18-octamethyl-a,c-biladiene dihydrobromide salt (10) with copper(II) acetate afforded copper(II) 3,7,8,12,13,17,18-octamethyl-1,20-dihydro porphyrin (13) (39% yield), which, upon demetalation, yielded the meta l-free 3,7,8,12,13,17,18-octamethyl-1,20-dihydroporphyrin (14) (48% yi eld). With the substrate thyl)-2,3,7,8,12,13,17,18-octamethyl-a,c-bila diene dihydrobromide (15), the metal-catalyzed cyclization process pro duced copper(II) 3,7,8,12,13,17,18-octamethyl-1,20-dihydroporphyrin (1 8) (27 % yield) and copper(II) ,18-heptamethyl-3-methylidene-2,3-dihyd roporphyrin (23) (19 % yield). Upon demetalation of the copper dihydro porphyrin 18, )-2,3,7,8,12,13,17,18-octamethyl-20'-homoporphyrin (28) (16.5 % yield) was isolated; demetalation of copper(II) ,18-heptamethy l-3-methylidene-2,3-dihydroporphyrin (23) yielded the free base ,18-he ptamethyl-3-methylidene-2,3-dihydroporphyrin (25) (24% yield). Using c hromium(III) hydroxy acetate as the oxidant (in place of copper(II)), 3,7,8,12,13,17,18-nonamethyl-1,20-dihydroporphyrin (5) (55-62%) was ob tained from the 1,2,3,7,8,12,13,17,18,19-decamethyl-a,c-biladiene salt 3. Mechanisms of macrocycle formation from a,c-biladiene salts, promo ted by either copper(II) or chromium(III), appear to proceed via pathw ays closely resembling the electrochemical cyclization reaction of 1,1 9-dimethyl-a,c-biladiene salts.