161690-41-1Relevant articles and documents
Effect of meso-substituents on the osmium tetraoxide reaction and pinacol-pinacolone rearrangement of the corresponding vic-dihydroxyporphyrins
Chen,Medforth,Smith,Alderfer,Dougherty,Pandey
, p. 3930 - 3939 (2007/10/03)
To investigate the effects of electron-donating and electron-withdrawing substituents upon the reaction of porphyrins with osmium tetraoxide, and the pinacol-pinacolone rearrangement of the resulting diols, a series of meso-substituted porphyrins were prepared by total synthesis. Porphyrins with electron-donating substitutents at the meso-positions gave vic-dihydroxychlorins in which the adjacent pyrrole subunit was predominantly oxidized. No such selectivity was observed in a porphyrin containing a methoxycarbonyl as the electron-withdrawing group, whereas a formyl substituent again resulted in oxidation at the pyrrole unit adjacent to the meso-substituent. Under pinacol-pinacolone conditions, vic-dihydroxy chlorins containing 4-methoxyphenyl or 3,5-dimethoxyphenyl groups at the meso-position showed preferential migration of the ethyl group over the methyl group to give 8-ketochlorins, whereas the diol with an n-heptyl substituent under similar reaction conditions gave both 7- and 8-ketochlorins. In contrast, the diol containing a meso-formyl substituent produced the corresponding 7-ketochlorin exclusively. These results indicate that it is not possible to predict the reactivity of meso-substituted porphyrins in the osmium tetraoxide reaction nor the general substituent migratory aptitudes in the pinacol-pinacolone rearrangement based on simple electronic arguments, most likely because many parameters (e.g., meso-β-pyrrolic steric crowding and long-range electronic effects) ultimately determine the reactivity. The structural assignments of the porphyrin diols and the keto-analogues were confirmed by extensive 1H NMR studies; some of the dihydroxychlorins and ketochlorins were found to display unusual features in their 1H NMR spectra.
SYNTHESES OF REGIOSPECIFICALLY MESO FUNCTIONALIZED DIPYRROMETHANES, PORPHYRINS, AND DIPHENYLETHANE-LINKED BISPORPHYRINS
Lee, David A.,Brisson, Jean M.,Smith, Kevin M.
, p. 131 - 136 (2007/10/02)
Acid catalyzed condensation of 2-unsubstituted pyrroles with diethyl acetals permits preparation, in good yields, of a variety of meso-functionalized dipyrromethanes.Subsequent use in the so-called MacDonald "2+2" condensation provides 5-functionalized po
