Nucleophilic Ring Opening of meso-Substituted 5-Oxaporphyrin by Oxygen, Nitrogen, Sulfur, and Carbon Nucleophiles

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• 作者：Kazuhisa Kakeya ; Masakatsu Aozasa ; Tadashi Mizutani ; Yutaka Hitomi ; Masahito Kodera
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：March 21, 2014
• 年：2014
• 卷：79
• 期：6
• 页码：2591-2600
• 全文大小：457K
• 年卷期：v.79,no.6(March 21, 2014)
• ISSN：1520-6904

文摘

Nucleophilic ring opening of 23H-[21,23-didehydro-10,15,20-tris(4-methoxycarbonylphenyl)-5-oxaporphyrinato](trifluoroacetato)zinc(II) with various nucleophiles such as alkoxide, amine, thiolate, and enolate gave 19-substituted bilinone zinc complexes, and they were isolated as free base bilinones. An X-ray crystallographic study demonstrated that the product of 5-oxaporphyrin with sodium methoxide was 21H,23H-(4Z,9Z,15Z)-1,21-dihydro-19-methoxy-5,10,15-tris(4-methoxycarbonylphenyl)bilin-1-one with a helicoidal conformation. The structure of the product of 5-oxaporphyrin with an enolate of ethyl acetoacetate was 21H,22H,24H-(4Z,9Z,15Z,19E)-19-(1-ethoxycarbonyl-2-oxopropylidene)-5,10,15-tris(4-methoxycarbonylphenyl)-1,19,21,24-tetrahydrobilin-1-one, with three inner NH groups. The product with SH^{鈥?/sup> was also the same tautomer, 21H,22H,24H-19-thioxo-bilin-1-one, with three NH groups, while the products with RO鈥?/sup>, RNH₂, and RS鈥?/sup> nucleophiles were 21H,23H-bilin-1-ones with two inner NH groups. The first-order rate constants of the ring opening reaction of 5-oxaporphyrin with 1 M BnOH and BnSH in toluene at 303 K were 3.0 脳 10鈥? and 6.1 脳 10鈥? s鈥?, respectively. The ratio of the rate of alcohol to thiol was much higher than that with methyl iodide, suggesting that 5-oxaporphyrin reacted as a hard electrophile in comparison to methyl iodide. UV鈥搗isible spectra of 19-substituted bilinones in CHCl₃ at 298 K showed that the absorption maximum of the lower energy band was red-shifted in increasing order of O-substituted (645 nm), S-substituted (668 nm), N-substituted (699 nm), and C-substituted bilinones (706 nm).}