Light‐Driven Enantioselective Synthesis of Pyrroline Derivatives by a Radical/Polar Cascade Reaction

Rodríguez, Ricardo I.; Mollari, Leonardo; Alemán, J.

doi:10.1002/anie.202013020

Cited by 22 publications

(11 citation statements)

References 62 publications

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“…A plausible mechanism for the aldehyde arylation is presented in Scheme 3 based on previous literature reports [19,26,33,34] and our mechanistic investigation experiments. Upon blue light irradiation, the photocatalyst is excited generating the strongly oxidizing complex *Ir[dF(CF 3 )ppy] Subsequently, DABCO radical cation engage in a HAT event with aldehydes to generate acyl radicals.…”

Section: Resultsmentioning

confidence: 99%

“…This species was then used for reduction of (hetero)aryl and alkyl halides, and subsequent carboarylation of several styrenes. Alemán and co-workers also published the use of a photogenerated DABCO radical cation in a distal β-carbonyl enantioselective C-H functionalization for the synthesis of pyrroline derivatives [26] (Figure 2d). The latter is, to the best of our knowledge, the only work reporting a direct substrate C-H bond functionalization using DABCO as a hydrogen atom abstractor in a photocatalytic strategy for synthetic purposes.…”

Section: Introductionmentioning

confidence: 99%

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DABCO-promoted photocatalytic C–H functionalization of aldehydes

Santos¹,

Dupim²,

Souza³

et al. 2021

Beilstein J. Org. Chem.

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Herein we present a direct application of DABCO, an inexpensive and broadly accessible organic base, as a hydrogen atom transfer (HAT) abstractor in a photocatalytic strategy for aldehyde C–H activation. The acyl radicals generated in this step were arylated with aryl bromides through a well stablished nickel cross-coupling methodology, leading to a variety of interesting aryl ketones in good yields. We also performed computational calculations to shine light in the HAT step energetics and determined an optimized geometry for the transition state, showing that the hydrogen atom transfer between aldehydes and DABCO is a mildly endergonic, yet sufficiently fast step. The same calculations were performed with quinuclidine, for comparison of both catalysts and the differences are discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

DABCO-promoted photocatalytic C–H functionalization of aldehydes

Santos¹,

Dupim²,

Souza³

et al. 2021

Beilstein J. Org. Chem.

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“…Over the last decades, significant progress has been made in photoredox catalysis for the synthesis of racemic pyrroline. , In 2020, the Alemán group synthesized optically active substituted cyclic imines by a photoredox/chiral-at-rhodium(III) dual catalytic strategy (Scheme ). This procedure requires acyl imidazole 369 and ketimines 370 to provide the substituted cyclic imines 371 via a HAT, radical coupling, and cyclization process. The desired products were obtained in high yields and excellent enantioselectivities, tolerating a broad range of functional groups.…”

Section: Visible-light-induced Asymmetric Catalysismentioning

confidence: 99%

Recent Development of Bis-Cyclometalated Chiral-at-Iridium and Rhodium Complexes for Asymmetric Catalysis

2021

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The field of asymmetric catalysis has been developing to access synthetically efficacious chiral molecules from the last century. Although there are many sustainable ways to produce nonracemic molecules, simplified and unique methodologies are always appreciated. In the recent developments of asymmetric catalysis, chiral-at-metal Lewis acid catalysis has been recognized as an attractive strategy. The catalysts coordinatively activate a substrate while serving the sole source of chirality by virtue of its helical environment. These configurationally stable complexes were utilized in a large number of asymmetric transformations, ranging from asymmetric Lewis acid catalysis to photoredox and electrocatalysis. Here we provide a comprehensive review of the current advancements in asymmetric catalysis utilizing iridium and rhodium-based chiral-at-metal complexes as catalysts. First, the asymmetric transformations via LUMO and HOMO activation assisted by a chiral Lewis acid catalyst are reviewed. In the second part, visible-light-induced asymmetric catalysis is summarized. The asymmetric transformation via the electricity-driven method is discussed in the final section.

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“…In recent decades, β-C(sp 3 )–H functionalization of carbonyls has attracted extensive attention in organic synthesis. 1–3 Despite the tremendous advances in the development of photocatalytic strategies, 4 achieving a catalytic version of the activation of β-C(sp 3 )–H groups with carbonyls remains an elusive task. For example, MacMillan and coworkers developed the 5π-electron (5πe − ) activation mode for the direct β-C(sp 3 )–H functionalization of saturated aldehydes and ketones by combining photoredox catalysis with organocatalysis (Scheme 1A, I).…”

Section: Introductionmentioning

confidence: 99%