A tin-complexation strategy for use with diverse acylation methods in the preparation of 1,9-diacyldipyrromethanes.
The acylation of dipyrromethanes to form 1,9-diacyldipyrromethanes is an essential step in the rational synthesis of porphyrins. Although several methods for acylation are available, purification is difficult because 1,9-diacyldipyrromethanes typically streak extensively upon chromatography and give amorphous powders upon attempted crystallization. A solution to this problem has been achieved by reacting the 1,9-diacyldipyrromethane with Bu(2)SnCl(2) to give the corresponding dibutyl(5,10-dihydrodipyrrinato)tin(IV) complex. The reaction is selective for dipyrromethanes that bear acyl groups at both the 1- and 9-positions but otherwise is quite tolerant of diverse substituents. The diacyldipyrromethane-tin complexes are stable to air and water, are highly soluble in common organic solvents, crystallize readily, and chromatograph without streaking. Four methods (Friedel-Crafts, Grignard, Vilsmeier, benzoxathiolium salt) were examined for the direct 1,9-diacylation of a dipyrromethane or the 9-acylation of a 1-acyldipyrromethane. In each case, treatment of the crude reaction mixture with Bu(2)SnCl(2) and TEA at room temperature enabled facile isolation of multigram quantities of the 1,9-diacyldipyrromethane-tin complex. The diacyldipyrromethane-tin complexes could be decomplexed with TFA in nearly quantitative yield. Alternatively, use of a diacyldipyrromethane-tin complex in a porphyrin-forming reaction (reduction with NaBH(4), acid-catalyzed condensation with a dipyrromethane, DDQ oxidation) afforded the desired free base porphyrin in yield comparable to that obtained from the uncomplexed diacyldipyrromethane. The acylation/tin-complexation strategy has been applied to a bis(dipyrromethane) and a porphyrin-dipyrromethane. In summary, the tin-complexation strategy has broad scope, is compatible with diverse acylation methods, and greatly facilitates access to 1,9-diacyldipyrromethanes.
Tamaru
Shun-ichi
S
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
Yu
Lianhe
L
Youngblood
W Justin
WJ
Muthukumaran
Kannan
K
Taniguchi
Masahiko
M
Lindsey
Jonathan S
JS
D000215:Acylation; D018360:Crystallography, X-Ray; D007202:Indicators and Reagents / Q000737:chemistry; D008697:Methane / Q000031:analogs & derivatives* / Q000138:chemical synthesis*; D000432:Methanol / Q000031:analogs & derivatives; D015394:Molecular Structure; D009947:Organotin Compounds / Q000737:chemistry*; D011166:Porphyrins / Q000138:chemical synthesis; D011758:Pyrroles / Q000138:chemical synthesis* / Q000737:chemistry
D007202:Indicators and Reagents; D009947:Organotin Compounds; D011166:Porphyrins; D011758:Pyrroles; D008697:Methane; D000432:Methanol