%0 Journal Article
%A Shi, Xianglin
%A Amin, Sk. Rasidul
%A Liebeskind, Lanny S.
%D 2000
%T 3-Cyclobutenyl-1,2-dione-Substituted Porphyrins. A General and
Efficient Entry to Porphyrin−Quinone and
Quinone−Porphyrin−Quinone Architectures
%U https://acs.figshare.com/articles/journal_contribution/3-Cyclobutenyl-1_2-dione-Substituted_Porphyrins_A_General_and_Efficient_Entry_to_Porphyrin_Quinone_and_Quinone_Porphyrin_Quinone_Architectures/3719673
%R 10.1021/jo9912799.s002
%2 https://acs.figshare.com/ndownloader/files/5811369
%K nonvinylogous system
%K porphyrin rings
%K vinylic Grignard reagents
%K vinylogous squarylporphyrin
%K UV
%K porphyrinic cyclobutenediones
%K dihedral angle
%K side products
%K tin reagent
%K nonadjacent meso
%K cyclobutenedione chemistry
%K zinc bromoporphyrins
%K cyclobutenedione chromophores
%K porphyrinic monoquinones
%K Efficient Entry
%K interconvertable atropisomers
%X A new and efficient synthesis of meso-linked porphyrin−quinone dyads and quinone−porphyrin−quinone triads has been developed via the intermediacy of porphyrins bearing 3-cyclobutenyl-1,2-dione and 3-(1-ethenyl)cyclobutenyl-1,2-dione substituents at one or two nonadjacent meso-positions.
The free-base porphyrins 5-bromo-10,20-diphenylporphyrin and 5,15-dibromo-10,20-diphenylporphyrin undergo facile palladium-catalyzed Stille coupling with 3-isopropoxy-2-tri-n-butylstannylcyclobutene-1,2-dione to produce the corresponding mono- and bis(3-cyclobutenyl-1,2-dione)-substituted porphyrins in good yields. In contrast, the zinc bromoporphyrins reacted with the same
tin reagent only slowly and with the formation of side products. The free-base bromoporphyrins
also were coupled with tri-n-butylvinyltin to afford vinylporphyrins in very good yields. 5,15-Diphenyl-10-vinylporphyrin was converted into trans-bromovinylporphyrin, which underwent facile
Stille coupling with 3-isopropoxy-2-tri-n-butylstannylcyclobutene-1,2-dione to afford the vinylogous
3-cyclobutenyl-1,2-dione-substituted porphyrin. The molecular structure of 5,15-bis(3-cyclobutenyl-1,2-dione)-10,20-diphenylporphyrin(Zn) was determined by X-ray crystallography. Although the
data revealed a fairly large dihedral angle between the cyclobutenedione and the porphyrin rings
(57°), the UV−vis spectra of both the mono- and bis(3-cyclobutenyl-1,2-dione)-substituted porphyrins
showed B- and Q-band red shifts indicative of strong electronic coupling between the porphyrin
and cyclobutenedione chromophores in solution. Introduction of a double bond between the
cyclobutenedione and porphyrin rings resulted in a significant red shift of both the B- and Q-bands
compared to those of the nonvinylogous system. All porphyrinic cyclobutenediones were metalated
with zinc and then, using established cyclobutenedione chemistry, converted into a variety of
porphyrin−quinones in excellent yields with aryllithium and vinylic Grignard reagents. From the
mono(3-cyclobutenyl-1,2-dione)-substituted porphyrin, 7, a variety of directly linked monoquinone−porphyrin dyads were easily synthesized. Substituents could also be introduced at the free meso-position of 7 by bromination followed by palladium-catalyzed cross-coupling reactions, and additional
porphyrinic monoquinones were then prepared from these starting materials. The vinylogous
squarylporphyrin was converted into a double bond linked porphyrin−quinone via reaction with
phenyllithium followed by thermal rearrangement and oxidation. As a result of the hindered rotation
around the C−C bond between the porphyrin and the quinone, pairs of stable, separable, and
thermally interconvertable atropisomers of porphyrin−quinones were obtained from 5,15-bis(3-cyclobutenyl-1,2-dione)-10,20-diphenylporphyrin(Zn). The structure of one of the atropisomers was
determined by X-ray crystallography.
%I ACS Publications