Photoredox/palladium-cocatalyzed enantioselective alkylation of secondary benzyl carbonates with 4-alkyl-1,4-dihydropyridines

Shen, Xu; Qian, Linlin; Yu, Shouyun

doi:10.1007/s11426-019-9732-5

Cited by 22 publications

(9 citation statements)

References 77 publications

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“…DIPEA ( E 1/2 = +0.68 V vs SCE) quenches visible-light-excited Ir(III)* ( E 1/2 (Ir III */Ir II ) = +0.66 V vs SCE) to generate a low-valent Ir(II) complex and the radical cation DIPEA •+ . ,,, Meanwhile, Pd(0) oxidatively adds to the allylic acetate 1 to give a (π-allyl)Pd II complex A . The single-electron reduction of A by an Ir(II) complex can generate the (π-allyl)Pd I complex B , which can equilibrate with an allylic radical species C and a Pd(0) species. , The second oxidative addition of another allylic acetate 1 to B would give the bis(π-allyl)Pd III complex D equilibrated with bis(η 1 -allyl)Pd III complex D′ (path a). − Alternatively, allylic radical species C is trapped by (π-allyl)Pd II complex A to generate D / D′ (path b). ,− ,,,, Reductive elimination − from D / D′ yields the homocoupling product 2 and the Pd(I) species E. ,,,, Finally single-electron reduction of E most likely by the Ir(II) complex would regenerate Pd(0). ,,, The Pd(III) intermediate D / D′ could also be reduced to a bis(allyl)Pd II species and then undergo a reductive elimination − to deliver the final product 2 (for more detailed discussions, see Figures S7 and S8). , …”

Section: Results and Discussionmentioning

confidence: 99%

“…We have recently achieved enantioselective photoredox/Pd-cocatalyzed allylic alkylation of the racemic allylic acetates with 4-alkyl-1,4-dihydropyridines. , During this investigation, we could observe a mixture of the reductive homocoupling of allylic acetates as the side products. 4-Alkyl-1,4-dihydropyridines serve as both the alkylation reagents for the allylic alkylation and the reductants for the reductive homocoupling.…”

Section: Introductionmentioning

confidence: 97%

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Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C₂-Symmetrical 1,5-Dienes

et al. 2021

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Transition-metal-catalyzed reductive coupling reactions have emerged as powerful protocols to construct C−C bonds. However, the development of enantioselective C(sp 3 )−C(sp 3 ) reductive coupling remains challenging. Herein, we report a highly regio-, diastereo-, and enantioselective reductive homocoupling of allylic acetates through cooperative palladium and photoredox catalysis using diisopropylethylamine or Hantzsch ester as a homogeneous organic reductant. This straightforward protocol enables the stereoselective construction of C(sp 3 )−C(sp 3 ) bonds under mild reaction conditions. A series of C 2 -symmetrical chiral 1,5-dienes were easily prepared with excellent enantioselectivities (up to >99% ee), diastereoselectivities (up to >95:5 dr), and regioselectivities (up to >95:5 rr). The resultant chiral 1,5-dienes can be directly used as chiral ligands in asymmetric synthesis, and they can be also transformed into other valuable chiral ligands.

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Section: Results and Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C₂-Symmetrical 1,5-Dienes

et al. 2021

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“…Since it was first reported in 1970 13 , 14 , catalytic asymmetric allylation has been studied extensively and now has widespread applications in organic synthesis 15 – 18 . However, few studies of catalytic asymmetric benzylation reactions have been reported 19 – 26 . This is probably because Tsuji–Trost allylation proceeds via a stable η 3 -allyl–palladium intermediate, whereas benzylation takes place via an unstable aromaticity-disrupted η 3 -benzyl–palladium complex (Fig.…”

Section: Introductionmentioning

confidence: 99%

Catalytic asymmetric Tsuji–Trost α−benzylation reaction of N-unprotected amino acids and benzyl alcohol derivatives

et al. 2022

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Catalytic asymmetric Tsuji–Trost benzylation is a promising strategy for the preparation of chiral benzylic compounds. However, only a few such transformations with both good yields and enantioselectivities have been achieved since this reaction was first reported in 1992, and its use in current organic synthesis is restricted. In this work, we use N-unprotected amino acid esters as nucleophiles in reactions with benzyl alcohol derivatives. A ternary catalyst comprising a chiral aldehyde, a palladium species, and a Lewis acid is used to promote the reaction. Both mono- and polycyclic benzyl alcohols are excellent benzylation reagents. Various unnatural optically active α-benzyl amino acids are produced in good-to-excellent yields and with good-to-excellent enantioselectivities. This catalytic asymmetric method is used for the formal synthesis of two somatostatin mimetics and the proposed structure of natural product hypoestestatin 1. A mechanism that plausibly explains the stereoselective control is proposed.

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“…Negishi cross-coupling of organozinc reagents with organohalides is a valuable reaction for a raft of applications, including total synthesis . The data gathered in this survey spanned 42 journal articles and 45 individual reactions. ,− The reaction data shows a preference for lower mol % values, particularly from papers published in the past decade. Interestingly, most ppm data points are distributed to lower ppm levels with more than 60% being below 500 ppm.…”

Section: Negishi Cross-couplingmentioning

confidence: 99%

Pd-Catalyzed Cross-Couplings: On the Importance of the Catalyst Quantity Descriptors, mol % and ppm

Horbaczewskyj

Fairlamb

2022

Org. Process Res. Dev.

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This Review examines parts per million (ppm) palladium concentrations in catalytic cross-coupling reactions and their relationship with mole percentage (mol %). Most studies in catalytic cross-coupling chemistry have historically focused on the concentration ratio between (pre)catalyst and the limiting reagent (substrate), expressed as mol %. Several recent papers have outlined the use of “ppm level” palladium as an alternative means of describing catalytic cross-coupling reaction systems. This led us to delve deeper into the literature to assess whether “ppm level” palladium is a practically useful descriptor of catalyst quantities in palladium-catalyzed cross-coupling reactions. Indeed, we conjectured that many reactions could, unknowingly, have employed low “ppm levels” of palladium (pre)catalyst, and generally, what would the spread of ppm palladium look like across a selection of studies reported across the vast array of the cross-coupling chemistry literature. In a few selected examples, we have examined other metal catalyst systems for comparison with palladium.

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Photoredox/palladium-cocatalyzed enantioselective alkylation of secondary benzyl carbonates with 4-alkyl-1,4-dihydropyridines

Cited by 22 publications

References 77 publications

Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C₂-Symmetrical 1,5-Dienes

Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C₂-Symmetrical 1,5-Dienes

Catalytic asymmetric Tsuji–Trost α−benzylation reaction of N-unprotected amino acids and benzyl alcohol derivatives

Pd-Catalyzed Cross-Couplings: On the Importance of the Catalyst Quantity Descriptors, mol % and ppm

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Photoredox/palladium-cocatalyzed enantioselective alkylation of secondary benzyl carbonates with 4-alkyl-1,4-dihydropyridines

Cited by 22 publications

References 77 publications

Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C2-Symmetrical 1,5-Dienes

Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C2-Symmetrical 1,5-Dienes

Catalytic asymmetric Tsuji–Trost α−benzylation reaction of N-unprotected amino acids and benzyl alcohol derivatives

Pd-Catalyzed Cross-Couplings: On the Importance of the Catalyst Quantity Descriptors, mol % and ppm

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Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C₂-Symmetrical 1,5-Dienes

Enantioselective Reductive Homocoupling of Allylic Acetates Enabled by Dual Photoredox/Palladium Catalysis: Access to C₂-Symmetrical 1,5-Dienes