jo9912799_si_002.pdf (1.01 MB)
3-Cyclobutenyl-1,2-dione-Substituted Porphyrins. A General and Efficient Entry to Porphyrin−Quinone and Quinone−Porphyrin−Quinone Architectures
journal contribution
posted on 2000-02-15, 00:00 authored by Xianglin Shi, Sk. Rasidul Amin, Lanny S. LiebeskindA 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.
History
Usage metrics
Categories
Keywords
nonvinylogous systemporphyrin ringsvinylic Grignard reagentsvinylogous squarylporphyrinUVporphyrinic cyclobutenedionesdihedral angleside productstin reagentnonadjacent mesocyclobutenedione chemistryzinc bromoporphyrinscyclobutenedione chromophoresporphyrinic monoquinonesEfficient Entryinterconvertable atropisomers
Licence
Exports
RefWorks
BibTeX
Ref. manager
Endnote
DataCite
NLM
DC