Iakovides P, Simpson D J, Smith K M
Department of Chemistry, University of California, Davis 95616.
Photochem Photobiol. 1991 Sep;54(3):335-43. doi: 10.1111/j.1751-1097.1991.tb02025.x.
The ascorbic acid/organic base photoreduction of zinc(II) porphyrins was investigated. It was established that certain substituents can direct the photoreduction to the site of the macrocycle to which they are attached. For example, zinc(II) vinylporphyrins (8, 12, 16, 20) are photoreduced with cis stereochemistry on the ring bearing the vinyl group to give the corresponding chlorins. Zinc(II) acetylporphyrins (22, 24) were likewise reduced to chlorins such that cis-hydrogenation took place on the ring bearing the acetyl group. Zinc(II) formylporphyrins 33 also appear to reduce at the ring bearing the formyl group. When the zinc(II) acrylic porphyrin 28 was photoreduced, reduction did take place at the ring bearing the acrylic side chain, but migration of the acrylate double bond was very rapid, and the product isolated was the corresponding porphyrin propionate 30. Reduction of a zinc(II) porphyrin 35 bearing both a vinyl group and a nuclear carboxylic ester took place at the ring bearing the carboxylic ester. The reaction provides a general method for regioselective synthesis of chlorins from zinc(II) porphyrins without any evidence of formation of over-reduction products characteristic of many other procedures for formation of chlorins from porphyrin precursors.
研究了锌（II）卟啉的抗坏血酸/有机碱光还原反应。已确定某些取代基可将光还原导向它们所连接的大环部位。例如，锌（II）乙烯基卟啉（8、12、16、20）在带有乙烯基的环上以顺式立体化学进行光还原，生成相应的二氢卟吩。锌（II）乙酰基卟啉（22、24）同样被还原为二氢卟吩，使得在带有乙酰基的环上发生顺式氢化。锌（II）甲酰基卟啉33似乎也在带有甲酰基的环上发生还原。当锌（II）丙烯酸卟啉28进行光还原时，确实在带有丙烯酸侧链的环上发生了还原，但丙烯酸双键的迁移非常迅速，分离得到的产物是相应的卟啉丙酸酯30。同时带有乙烯基和核羧酸酯的锌（II）卟啉35在带有羧酸酯的环上发生还原。该反应提供了一种从锌（II）卟啉区域选择性合成二氢卟吩的通用方法，没有任何证据表明形成了许多其他从卟啉前体形成二氢卟吩的方法所特有的过度还原产物。
