- Synthesis of tailored hydrodipyrrins and their examination in directed routes to bacteriochlorins and tetradehydrocorrins
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The chemistry of reduced tetrapyrroles is less developed than that of the fully unsaturated (porphyrin) analogues, yet is of comparable importance given the natural roles of hydroporphyrins (e.g., chlorophylls, bacteriochlorophylls) and contracted hydropo
- Zhang, Shaofei,Nagarjuna Reddy, Muthyala,Mass, Olga,Kim, Han-Je,Hu, Gongfang,Lindsey, Jonathan S.
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p. 11170 - 11189
(2017/10/03)
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- Access to indoles via Diels-Alder reactions of 5-methylthio-2-vinylpyrroles with maleimides
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Diels-Alder reactions of 5-methylthio-2-vinyl-1H-pyrroles with maleimides followed by isomerization gave tetrahydroindoles in moderate to good yield. Aromatization using activated MnO2 in refluxing toluene gave the corresponding 2-methylthioindoles in good yields, and demethylthioation using Raney nickel gave the 2-H indoles in excellent yields. The protection of the adducts produced aromatization in improved yield, demonstrating the effectiveness of the methylthio group as a protecting group for pyrroles; however, 5-methylthio-2-vinylpyrrole was shown to perform with slightly less efficiency than 2-vinylpyrrole in Diels-Alder reactions, indicating the protective group was more deactivating than desired. This route toward indoles offers high convergency and conveniently available starting materials that are easily purified. Bis-methylthioated vinylpyrroles were shown to have potential as highly activated Diels-Alder dienes.
- Noland, Wayland E.,Lanzatella, Nicholas P.,Dickson, Rozalin R.,Messner, Mary E.,Nguyen, Huy H.
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p. 795 - 808
(2013/08/23)
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- Synthesis of 5-substituted pyrrole-2-carboxaldehydes. Part I. Generation of formal 5-lithiopyrrole-2-carboxaldehyde equivalents by bromine-lithium exchange of 2-bromo-6-(diisopropylamino)-1-azafulvene derivatives
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The first known lithiated 1-azafulvene derivatives, e.g., 8 and 13a, were generated by a low-temperature bromine-lithium exchange procedure with tert-butyllithium.These lithio species show substantial stability at /=-90 deg C because, at these temperatures, the sterically demanding 6-diisopropylamino moiety, unlike the dimethylamino group, completely inhibits nucleophilic addition to C-6.At higher temperatures, the addition of tert-butyllithium to C-6 is significant and it can become the dominant process.The lithio species 8 is a useful formal equivalent of 5-lithiopyrrole-2-carboxaldehyde since, on reaction with electrophilic reagents and subsequent hydrolysis, a wide variety of regiochemically pure 5-substituted pyrrole-2-carboxaldehydes is formed.The 6-dialkylamino-1-azafulvenes described herein exist predominantly or exclusively as the syn conformer in solution at room temperature.This conformational preference is confirmed by a significance NOE effect between H-4 and H-6 in the parent diisopropylamino compound 3f.The origin of the syn conformational preference stems from a substantial contribution of the charge-separated form 16 to the ground state structure of these compounds, a phenomenon that is strongly supported by variable temperature NMR measurements on 2-bromo-6-diisopropylamino-1-azafulvene (3c).Key words: 2-bromo-6-diisopropylamino-1-azafulvenes, stereochemistry, lithiation, pyrolle-2-carboxaldehydes.
- Berthiaume, Sylvie L.,Bray, Brian L.,Hess, Petr,Liu, Yanzhou,Maddox, Michael L.,et al.
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p. 675 - 684
(2007/10/02)
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- 216. Lithiated Azafulvenes by Halogen/Metal Interchange of Brominated 6-(Diisopropylamino)-1-azafulvene Derivatives. Novel Synthesis of 5-Mono- and 4,5-Disubstituted 1H-Pyrrole-2-carbaldehydes
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The first known lithiated 1-azafulvene derivatives were generated by low-temperature halogen/metal interchange, with t-BuLi, from the corresponding brominated 6-diisopropylamino compounds 3b and 12.These Li species reacted with sundry electrophilic reagents to give products which, on the basic hydrolysis, were converted into 5-mono- or 4,5-disubstituted pyrrole-2-carbaldehydes 10 and 16, respectively.
- Bray, Brian L.,Hess, Petr,Muchowski, Joseph M.,Scheller, Markus E.
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p. 2053 - 2057
(2007/10/02)
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