Probing the origin of the stereoselectivity and enantioselectivity of cobalt-catalyzed [2 + 2] cyclization of ethylene and enynes

Lin, Lu; Dai, Chao; Zhu, Jun

doi:10.1039/d0qo01412e

Cited by 8 publications

(8 citation statements)

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“…Meanwhile, we also considered the β-hydrogen transfer process (i.e., IM6 ! TS5', see Figure 4) as proposed by previous study, 38,54,55 yet the barrier is predicted to be 11.2 kcal mol À1 higher than that of our β-hydrogen elimination course (i.e., IM6 ! TS5), which will not be further discussed in this study.…”

Section: Stage I: Oxidative Dimerization Followed By Reductive Elimin...supporting

confidence: 70%

“…After generating the metal cycloheptene IM6 in Stage II, the β‐ H transfer to the Co(III)‐center can be easily achieved via a small barrier of 5.6 kcal mol −1 (i.e., IM6 → TS5 , see Figure 4), accompanied by the cycloheptane ring opening leading to the chiral slightly unstable (Z)‐allyl Co(III)‐hydride complex IM7 . Meanwhile, we also considered the β ‐hydrogen transfer process (i.e., IM6 → TS5 ', see Figure 4 ) as proposed by previous study, 38,54,55 yet the barrier is predicted to be 11.2 kcal mol −1 higher than that of our β ‐hydrogen elimination course (i.e., IM6 → TS5 ), which will not be further discussed in this study.…”

Section: Resultsmentioning

confidence: 99%

“…Compared with previously reported reactions, the reactants 1,3‐alkynes and most ethylenes are commercially available and inexpensive raw materials. Although the authors proposed a reaction course and Zhu et al studied the mechanism by using the simplified models 38 . the detailed mechanistic study of this unprecedented catalytic reaction, particularly the rate‐determining step (RDS), the origins of good enantiomeric‐ and regio‐selectivity of the product, remain elusive.…”

Section: Introductionmentioning

confidence: 99%

“…studied the mechanism by using the simplified models. 38 the detailed mechanistic study of this unprecedented catalytic reaction, particularly the rate-determining step (RDS), the origins of good enantiomeric-and regio-selectivity of the product, remain elusive.…”

Section: Introductionmentioning

confidence: 99%

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Mechanistic study of cobalt(I)‐catalyzed asymmetric coupling of ethylene and enynes to functionalized cyclobutanes

et al. 2021

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Density functional theory (DFT) calculations have been performed to gain insight into the reaction mechanism of the Co(I)-catalyzed asymmetric [2 + 2] cycloaddition reaction of enyne 1a with ethylene 2 to give the functionalized cyclobutene E-4a possessing a chiral, all-carbon quaternary center in the ring framework (Science, 361,(68)(69)(70)(71)(72). This study reveals that the whole catalysis can be characterized via three stages: (i) oxidative dimerization followed by reductive elimination gives the intermediate IM3, (ii) the alkenyl-Co(III) metallacycloheptene IM6 formation with the addition of another equivalent ethylene via an oxidative dimerization process, (iii) β-Hydrogen elimination and reductive elimination from IM6 to result in the final product E-4a and regenerate the active speices IM1 for the next catalytic cycle. Each stage is kinetically and thermodynamically feasible for experimental realization under mild conditions, and the formation of the alkenyl-Co(III) metallacycloheptene IM6, with a barrier of 27.2 kcal mol À1 (i.e., IM2 ! TS4), should be the rate-determining step (RDS) during the whole catalysis. In addition, the origins of enantioselectivity and regioselectivity of the product are discussed.

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Section: Stage I: Oxidative Dimerization Followed By Reductive Elimin...supporting

confidence: 70%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mechanistic study of cobalt(I)‐catalyzed asymmetric coupling of ethylene and enynes to functionalized cyclobutanes

et al. 2021

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“…For this, we turned to reactions of 1,3-enynes with ethylene (Figure ). Most remarkably, a highly ligand-dependent reaction ensued giving either a simple [2 + 2]-addition to a vinylcyclobutene ( 16 ) or a product ( 17 ) derived from the subsequent hydrovinylation of 16 (Figure A) , Among the Co-complexes of 1, n -diphenylphosphinoalkanes, DPPP and 1,1′-bis(diphenylphosphino)ferrocene (DPPF) were most active, selectively yielding almost exclusively the cycloaddition product 16 (for R = n- Bu) at low temperature, but yielding 17 on prolonged reaction time. Among the chiral phosphines, phosphinooxazolines showed the best selectivity with the reaction proceeding even at −20 °C when the catalyst was activated with either trimethyl aluminum, MAO, or Et 2 AlCl.…”

Section: Enantioselective [2 + 2]-cycloaddition Between Alkynes and A...mentioning

confidence: 99%

A New Paradigm in Enantioselective Cobalt Catalysis: Cationic Cobalt(I) Catalysts for Heterodimerization, Cycloaddition, and Hydrofunctionalization Reactions of Olefins

et al. 2021

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Conspectus One of the major challenges facing organic synthesis in the 21st century is the utilization of abundantly available feedstock chemicals for fine chemical synthesis. Regio- and enantioselective union of easily accessible 1,3-dienes and other feedstocks like ethylene, alkyl acrylates, and aldehydes can provide valuable building blocks adorned with latent functionalities for further synthetic elaboration. Through an approach that relies on mechanistic insights and systematic examination of ligand and counterion effects, we developed an efficient cobalt-based catalytic system [(P∼P)CoX2/Me3Al] (P∼P = bisphosphine) to effect the first enantioselective heterodimerization of several types of 1,3-dienes with ethylene. In addition to simple cyclic and acyclic dienes, siloxy-1,3-dienes participate in this reaction, giving highly functionalized, nearly enantiopure silyl enolates, which can be used for subsequent C–C and C–X bond-forming reactions. As our understanding of the mechanism of this reaction improved, our attention was drawn to more challenging partners like alkyl acrylates (one of the largest volume feedstocks) as the olefin partners instead of ethylene. Prompted by the intrinsic limitations of using aluminum alkyls as the activators for this reaction, we explored the fundamental chemistry of the lesser known (P∼P)Co(I)X species and discovered that in the presence of halide sequestering agents, such as sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBARF) or (C6F5)3B, certain chiral bisphosphine complexes are superb catalysts for regio- and enantioselective heterodimerization of 1,3-dienes and alkyl acrylates. We have since found that these cationic Co(I) catalysts, most conveniently prepared in situ by reduction of the corresponding cobalt(II) halide complexes by zinc in the presence of NaBARF, promote enantioselective [2 + 2]-cycloaddition between alkynes and an astonishing variety of alkenyl derivatives to give highly functionalized cyclobutenes. In reactions between 1,3-enynes and ethylene, the [2 + 2]-cycloaddition between the alkyne and ethylene is followed by a 1,4-addition of ethylene in a tandem fashion to give nearly enantiopure cyclobutanes with an all-carbon quaternary center, giving a set of molecules that maps well into many medicinally relevant compounds. In another application, we find that the cationic Co(I)-catalysts promote highly selective hydroacylation and 1,2-hydroboration of prochiral 1,3-dienes. Further, we find that a cationic Co(I)-catalyst promotes cycloisomerization followed by hydroalkenylation of 1,6-enynes to produce highly functionalized carbo- and heterocyclic compounds. Surprisingly the regioselectivity of the alkene addition depends on whether it is a simple alkene or an acrylate, and the acrylate addition produces an uncommon Z-adduct. This Account will provide a summary of the enabling basic discoveries and the attendant developments that led to the unique cationic Co(I)-complexes as catalysts for disparate C–C and C–B bond-forming reactions. It...

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Effect of ligand coordination on the mechanism and regioselectivity of cobalt-catalyzed hydroboration/cyclization of 1,6-enynes

Fu,

Liu,

Chen

et al. 2023

Journal of Catalysis

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Probing the origin of the stereoselectivity and enantioselectivity of cobalt-catalyzed [2 + 2] cyclization of ethylene and enynes

Abstract: The cyclobutane unit is important to prepare complex natural products with a biological activity due to a high ring strain. Among various approaches, [2+2] cycloaddition is one of the major...

Cited by 8 publications

References 64 publications

Mechanistic study of cobalt(I)‐catalyzed asymmetric coupling of ethylene and enynes to functionalized cyclobutanes

Mechanistic study of cobalt(I)‐catalyzed asymmetric coupling of ethylene and enynes to functionalized cyclobutanes

A New Paradigm in Enantioselective Cobalt Catalysis: Cationic Cobalt(I) Catalysts for Heterodimerization, Cycloaddition, and Hydrofunctionalization Reactions of Olefins

Effect of ligand coordination on the mechanism and regioselectivity of cobalt-catalyzed hydroboration/cyclization of 1,6-enynes

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