Expanded Scope of Synthetic Bacteriochlorins via Improved Acid Catalysis Conditions and Diverse Dihydrodipyrrin-Acetals
Expanded Scope of Synthetic Bacteriochlorins via Improved Acid Catalysis Conditions and Diverse Dihydrodipyrrin-Acetals
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DOI：
10.1021/jo9025572
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发表时间：
2010-02-19
影响因子：
3.6
通讯作者：
Lindsey, Jonathan S.
中科院分区：
文献类型：
--
作者：
Krayer, Michael;Ptaszek, Marcin;Lindsey, Jonathan S.
由于细菌绿素在近红外光谱区有很强的吸收，因此它在光化学研究中具有广泛的应用前景。用于二氢二吡啉-缩醛（在吡咯啉环中带有偕二甲基）的自缩合的现有酸催化条件[BF 3中心点O（Et）（2）在室温下在CH 3CN中]通常提供三种大环的混合物：预期的5-甲氧基菌绿素（MeOBC型）、5-未取代的菌绿素（HBC型）和游离碱B，D-四氢咕啉（TDC型）。在此，对>20种酸的广泛调查确定了四种有希望的酸催化条件，其中在室温下在CH 2Cl 2中的TMSOTf/2，6-二叔丁基吡啶是最有吸引力的，这是由于形成了作为唯一大环的5-甲氧基菌绿素，而不管二氢二吡咯-缩醛中的吡咯取代基（吸电子、给电子或无取代基）。按照标准路线制备了11种新的二氢二吡咯-缩醛。新的酸催化条件的应用已经提供了多种菌绿素（例如，带有烷基/酯、芳基/酯、二酯和无取代基）。考虑到合成步骤和产量形成的二氢二吡啉-缩醛和菌绿素的基础评价的合成计划，早期安装的菌绿素取代基通过二氢二吡啉-缩醛与后期安装通过衍生化的β-溴菌绿素。5-甲氧基菌绿素与NBS的治疗给区域选择性15-溴化时，没有吡咯取代基存在或当每个吡咯含有两个取代基;另一方面，β-乙氧羰基基团的存在下造成的损失的区域选择性。本文制备的15种新的细菌绿素在707-759 nm范围内表现出长波长吸收带，提供了对近红外区域的可调谐访问。总之，这项研究扩大了细菌绿素的基础研究和不同的应用范围。
Bacteriochlorins are attractive candidates for a wide variety of photochemical studies owing to their strong absorption in the near-infrared spectral region. The prior acid-catalysis conditions [BF3 center dot O(Et)(2) in CH3CN at room temperature] for self-condensation of a dihydrodipyrrin-acetal (bearing a geminal dimethyl group in the pyrroline ring) typically afforded a mixture of three macrocycles: the expected 5-methoxybacteriochlorin (MeOBC-type), a 5-unsubstituted bacteriochlorin (HBC-type), and a free base B,D-tetradehydrocorrin (TDC-type). Here, a broad survey of >20 acids identified four promising acid catalysis conditions of which TMSOTf/2,6-di-tert-butylpyridine in CH2Cl2 at room temperature was most attractive owing to formation of the 5-methoxybacteriochlorin as the sole macrocycle regardless of the pyrrolic substituents in the dihydrodipyrrin-acetal (electron-withdrawing, electron-donating, or no substituent). Eleven new dihydrodipyrrin-acetals were prepared following standard routes. Application of the new acid catalysis conditions has afforded diverse bacteriochlorins (e.g., bearing alkyl/ester, aryl/ester, diester, and no substituents) in a few days from commercially available starting materials. Consideration of the synthetic steps and yields for formation of the dihydrodipyrrin-acetal and bacteriochlorin underpins evaluation of synthetic plans for early installation of bacteriochlorin substituents via the dihydrodipyrrin-acetal Versus late installation via derivatization of beta-bromobacteriochlorins. Treatment of the 5-methoxybacteriochlorins with NBS gave regioselective 15-bromination when no pyrrolic substituents were present or when each pyrrole contained two substituents; on the other hand, the presence of a beta-ethoxycarbonyl group caused loss of regioselectivity. The 15 new bacteriochlorins prepared herein exhibit a long-wavelength absorption band in the range 707-759 nm, providing tunable access to the near-infrared region. Taken together, this study expands the scope of available bacteriochlorins for fundamental studies and diverse applications.