Pa. Liddell et al., NOVEL MACROCYCLES FROM METAL-CATALYZED OXIDATIVE CYCLIZATIONS OF A,C-BILADIENE SALTS, Journal of organic chemistry, 58(24), 1993, pp. 6681-6691
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.