Cinchona-based primary amine-catalyzed enantioselective aza-Michael reactions of pyrroles with α,β-unsaturated aldehydes

Lee, Su-Jeong; Ahn, Jun-Gi; Cho, Chang-Woo

doi:10.1016/j.tetasy.2014.09.002

Cited by 21 publications

(5 citation statements)

References 56 publications

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“…The Nazarov reaction process also can be regarded as an intramolecular Michael addition (5- endo - trig ) of the pyrrole with the appended propenoyl substituent. Intermolecular examples of such pyrrole C -alkylations date to as early as 1951 and were typically carried out with either activated reactants or somewhat forcing conditions. − Research in the past 15 years has shifted to unactivated reactants and implementation with mild Lewis acid catalysts and/or enantioselective catalysts (for a comprehensive set of references, see the Supporting Information; for a partial review, see ref ).…”

Section: Discussionmentioning

confidence: 99%

Construction of the Bacteriochlorin Macrocycle with Concomitant Nazarov Cyclization To Form the Annulated Isocyclic Ring: Analogues of Bacteriochlorophyll a

Zhang

Lindsey

2017

J. Org. Chem.

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Bacteriochlorophylls contain a bacteriochlorin macrocycle bearing an annulated fifth ring. The fifth ring, termed the isocyclic ring or ring E, is equipped with 13-oxo and 13-carbomethoxy substituents. Herein, a general route to stable, synthetic bacteriochlorophyll analogues is described. Knoevenagel condensation (∼40 mM, rt, CHCl, piperidine/AcOH/molecular sieves) of a dihydrodipyrrin-carboxaldehyde (AD half) and a dihydrodipyrrin substituted with a β-ketoester (BC half) forms a propenone bearing the two halves (a hydrobilin analogue). Subsequent treatment (0.2 mM) with acid (Yb(OTf), CHCN, 80 °C) promotes a double ring-closure process: (i) condensation between the α-position of pyrrole ring A and the α-acetal unit attached to pyrroline ring B forms the bacteriochlorin macrocycle, and (ii) Nazarov cyclization of the β-(propenoyl)-substituted ring C forms the isocyclic ring (E). Five new bacteriochlorins bearing various substituents (alkyl/alkyl, aryl, and alkyl/ester) at positions 2 and 3 (β-pyrrole sites, ring A) and 13 carboalkoxy groups (R = Me or Et) were constructed in 37-61% yield from the hydrobilin analogues. The BC half and AD half are available in five and eight steps, respectively, from the corresponding pyrrole-2-carboxaldehyde and unsaturated ketone. The bacteriochlorins exhibit absorption spectra typical of bacteriopheophytins (free base bacteriochlorophylls), with a strong near-infrared absorption band (707-751 nm).

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Section: Discussionmentioning

confidence: 99%

Construction of the Bacteriochlorin Macrocycle with Concomitant Nazarov Cyclization To Form the Annulated Isocyclic Ring: Analogues of Bacteriochlorophyll a

Zhang

Lindsey

2017

J. Org. Chem.

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“…The same research group could extend their aza-Michael reaction strategy to include the α,β-unsaturated aldehydes of type 205 this time under chiral primary amine catalysis (Scheme 74). [148] Using 20 mol% of cinchona-based primary amine C-47 as the organocatalyst, the N-functionalized pyrrolealcohol products 206, derived from the aza-Michael reaction of pyrroles 201 as N-centered nucleophile and α,β-unsaturated Scheme 73. Enantioselective aza-Michael reaction of pyrroles and its application in total synthesis of bromopyrrole alkaloids.…”

Section: Enantioselective Aza-michael Reactionsmentioning

confidence: 99%

“…Further exploration of the work for 4-bromo-5-iodo-1Hpyrrole-2-carbonitrile 201 b with different α,β-unsaturated aldehydes 205 revealed that the aza-Michael aldehyde products 207 were efficiently formed under the same reaction condition, despite two different alcohol products were obtained by varying the reduction steps (Scheme 75). [148] Reduction of the aza-Michael aldehyde products 207 with NaBH 4 as reducing agents, afforded the aza-Michael-alcohol products 208 in high enantioselectivity, albeit with moderate yield. While the same aza-Michael aldehyde products when with BH 3 • SMe 2 deliver the aza-Michael-alcohol products of type 209 insufficient reactivity and selectivity.…”

Section: Enantioselective Aza-michael Reactionsmentioning

confidence: 99%

Recent Advances in Metal‐ and Organocatalyzed Asymmetric Functionalization of Pyrroles

2021

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The wide occurrence of pyrroles in natural products and pharmaceuticals calls for novel synthetic methodologies for the efficient synthesis of enantiopure pyrroles. Owing to their highly reactive nature and wide-ranging chemical landscape, enormous efforts have been dedicated not only to their synthesis but also to the development of reactions using them as a platform and their utilization in the stereocontrolled synthesis of diverse molecules. In sharp contrast to the extensive studies devoted toward indoles, the asymmetric functionalization of pyrroles was less explored. Never-theless, the attractiveness of pyrroles for their selective functionalization to access natural product analogy, and medicinally useful architectures have witnessed tremendous growth in the last few years. Their effectiveness under both metal-and organocatalytic conditions currently encompasses a vast majority of enantioselective transformations. This review article aims to present a comprehensive overview of the catalytic asymmetric CÀ H as well as NÀ H functionalization of pyrroles reported from 2010 to now.

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“…[5][6][7][8] Traditionally, the aza-Michael reactions are often promoted by strong acidic or basic conditions that are incompatible for substrates containing acid or base sensitive functional groups (Scheme 1a). [9][10][11] Alternatively, a variety of transition metal and Brønsted catalysis including Cu, Ni, Co, Zr, Al, V, p-TsOH, etc., have been developed to circumvent the functional group intolerance issue. [12][13][14][15][16][17][18] However, many of these catalyst systems are air and/or moisture sensitive, rendering their practicality somewhat limited.…”

Section: Introductionmentioning

confidence: 99%

Hypervalent iodine-catalyzed conjugate addition with sulfonamides

Ariyarathna¹,

Ziegelmeyer²,

Li³

2021

Arkivoc

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A hypervalent iodine-catalyzed conjugate addition with a sulfonamide nucleophile is described here. This reaction utilizes catalytic amounts of iodoarene and oxidant for the generation of the active hypervalent iodine catalyst. Activation of the enone substrate by the hypervalent iodine catalyst enables the nitrogen nucleophile addition that eventually forms a useful -aminocarbonyl product. This hypervalent iodinecatalyzed Aza-Michael reaction represents an interesting alternative to existing conjugate addition protocols.

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Cinchona-based primary amine-catalyzed enantioselective aza-Michael reactions of pyrroles with α,β-unsaturated aldehydes

Cited by 21 publications

References 56 publications

Construction of the Bacteriochlorin Macrocycle with Concomitant Nazarov Cyclization To Form the Annulated Isocyclic Ring: Analogues of Bacteriochlorophyll a

Construction of the Bacteriochlorin Macrocycle with Concomitant Nazarov Cyclization To Form the Annulated Isocyclic Ring: Analogues of Bacteriochlorophyll a

Recent Advances in Metal‐ and Organocatalyzed Asymmetric Functionalization of Pyrroles

Hypervalent iodine-catalyzed conjugate addition with sulfonamides

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