@article{strachan_df o'shea_balasubramanian_lindsey_2000, title={Rational synthesis of meso-substituted chlorin building blocks}, volume={65}, ISSN={["1520-6904"]}, DOI={10.1021/jo991942t}, abstractNote={Chlorins provide the basis for plant photosynthesis, but synthetic model systems have generally employed porphyrins as surrogates due to the unavailability of suitable chlorin building blocks. We have adapted a route pioneered by Battersby to gain access to chlorins that bear two meso substituents, a geminal dimethyl group to lock in the chlorin hydrogenation level, and no flanking meso and β substituents. The synthesis involves convergent joining of an Eastern half and a Western half. A 3,3-dimethyl-2,3-dihydrodipyrrin (Western half) was synthesized in four steps from pyrrole-2-carboxaldehyde. A bromodipyrromethane carbinol (Eastern half) was prepared by sequential acylation and bromination of a 5-substituted dipyrromethane followed by reduction. Chlorin formation is achieved by a two-flask process of acid-catalyzed condensation followed by metal-mediated oxidative cyclization. The latter reaction has heretofore been performed with copper templates. Investigation of conditions for this multistep process led to copper-free conditions (zinc acetate, AgIO3, and piperidine in toluene at 80 °C for 2 h). The zinc chlorin was obtained in yields of ∼10% and could be easily demetalated to give the corresponding free base chlorin. The synthetic process is compatible with a range of meso substituents (p-tolyl, mesityl, pentafluorophenyl, 4-[2-(trimethylsilyl)ethynyl]phenyl, 4-iodophenyl). Altogether four free base and four zinc chlorins have been prepared. The chlorins exhibit typical absorption spectra, fluorescence spectra, and fluorescence quantum yields. The ease of synthetic access, presence of appropriate substituents, and characteristic spectral features make these types of chlorins well suited for incorporation in synthetic model systems.}, number={10}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Strachan, JP and DF O'Shea and Balasubramanian, T and Lindsey, JS}, year={2000}, month={May}, pages={3160–3172} }
 @article{littler_miller_hung_wagner_df o'shea_boyle_lindsey_1999, title={Refined synthesis of 5-substituted dipyrromethanes}, volume={64}, ISSN={["0022-3263"]}, DOI={10.1021/jo982015+}, abstractNote={5-Substituted dipyrromethanes are important precursors for the synthesis of meso-substituted porphyrins,1 expanded porphyrins, and porphyrin analogues.2 Several one-flask methods have been reported for the synthesis of 5-substituted dipyrromethanes by the condensation of an aldehyde and pyrrole using various combinations of acids and solvents.3-14 We previously reported a one-flask synthesis of dipyrromethanes in which an aldehyde is dissolved in a 40-fold excess of pyrrole with a catalytic amount of an acid at room temperature in the absence of any other solvent.8 This method has afforded good yields of 5-substituted dipyrromethanes bearing many types of functional groups.15 However, purification of the product is typically achieved by flash column chromatography, restricting application to the small-scale preparation of dipyrromethanes. Our objective in this study was to eliminate the use of chromatography during purification, thereby removing the major bottleneck to the synthesis of multigram quantities of dipyrromethanes. Upon examining the crude reaction mixture from the acid-catalyzed condensation of benzaldehyde in excess pyrrole, we found that the principal reaction products consist of the dipyrromethane (1), the N-confused dipyrromethane (2,3′-dipyrromethane) (2) and the tripyrrane (3) (Scheme 1). The presence of the N-confused dipyrromethane was surprising as this species had not been detected previously.8 Using GC we have examined the distribution of these products as a function of the pyrrole:benzaldehyde ratio and the acid catalyst. We have developed a purification process based on bulb-to-bulb distillation followed by recrystallization that affords analytically pure dipyrromethanes in multigram quantities. The condensation of pyrrole and benzaldehyde upon heating without added acids has also been examined.}, number={4}, journal={JOURNAL OF ORGANIC CHEMISTRY}, author={Littler, BJ and Miller, MA and Hung, CH and Wagner, RW and DF O'Shea and Boyle, PD and Lindsey, JS}, year={1999}, month={Feb}, pages={1391–1396} }