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. 2024 Mar;11(9):e2307074.
doi: 10.1002/advs.202307074. Epub 2023 Dec 15.

Radical-Dearomative Generation of Cyclohexadienyl Pd(II) toward the 3D Transformation of Nonactivated Phenyl Rings

Qi Fan  1 , Kai Jiang  1 , Bo Liu  2 , Huanfeng Jiang  1 , Xiaohui Cao  3 , Biaolin Yin  1
Affiliations

Radical-Dearomative Generation of Cyclohexadienyl Pd(II) toward the 3D Transformation of Nonactivated Phenyl Rings

Qi Fan et al. Adv Sci (Weinh). 2024 Mar.

Abstract

Traditional palladium-catalyzed dearomatization of (hetero)arenes takes place via an ionic pathway and usually requires elevated temperatures to overcome the energy barrier of the dearomative insertion step. Herein, a combination of the radical and two-electron pathways is disclosed, which enables room temperature dearomative 3D transformations of nonactivated phenyl rings with Pd(0) as the catalyst. Experimental results together with density functional theory (DFT) calculations indicate a versatile π-allyl Pd(II) species, cyclohexadienyl Pd(II), possibly is involved in the dearomatization. This species is generated by combining the cyclohexadienyl radical and Pd(I). The cyclohexadienyl Pd(II) provides chemoselective (carboamination and trieneylation), regioselective (1,2-carboamination), and diastereoselective (carbonyl-group directed face selectivity) conversions.

Keywords: carboamination; cyclohexadienyl Pd(II); radical dearomatization; trieneylation.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Developments of Pd‐catalyzed dearomatization, radical‐type dearomatization, and emerging excited palladium chemistry.
Scheme 2
Scheme 2
a) Reaction of 1a to 2a under standard conditions A: 0.2 mmol 1a, 5 mmol% Pd(PPh3)4, 10 mmol% Xantphos (L1), THF (0.1 m of 1a), 30 W blue LEDs irradiation, room temperature, and argon atmosphere. b) Crossover experiment. c) Radical trapping experiments. d) HRMS of reaction mixture. e) Reaction of control compound 8. f) Proposed mechanism. g) Computed energy profile of the proposed mechanism. Free energies in solution (in kcal mol−1) at the M06‐D3(SMD)/SDD/6‐311+G(d, p) //B3LYP‐D3/LanL2DZ/6‐31G(d) level are displayed.
Scheme 3
Scheme 3
The substrate scope of the dearomative 1,2‐carboamination. a reaction time: 36 h. b reaction time: 48 h. c dr >20:1.
Scheme 4
Scheme 4
a) Substrates scope; Mixture were provided for some of the products; a dr >20:1; b reaction time: 24 h; b) Calculated relative energy of the intermediates for 2ai and calculated relative energy of the transition states for 2ai.
Scheme 5
Scheme 5
a) Scope of the trieneylation. a reaction time: 48 h. b 10 mol% L1 was added and the reaction time was 40 h; b) Calculated energy level of the transition states for β‐H elimination and nucleophilic substitution of 4a. c) Calculated energy level of the transition states for β‐H elimination and nucleophilic substitution of 2f.
Scheme 6
Scheme 6
Gram‐scale synthesis and product derivatization. Conditions: i) Pd/C, H2 in balloon, 1 atm; ii) NMO/K2OsO4·2H2O; iii) N2H4·H2O; iv) Ph2SiH2; vi) O3 atmosphere. v) Pd/C, H2 in balloon, 1 atm.
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