Multicatalytic approach to one-pot stereoselective synthesis of secondary benzylic alcohols

Article abstract of DOI:10.1021/acs.orglett.1c00939

One-pot procedures bear the potential to rapidly build up molecular complexity without isolation and purification of consecutive intermediates. Here, we report multicatalytic protocols that convert alkenes, unsaturated aliphatic alcohols, and aryl boronic acids into secondary benzylic alcohols with high stereoselectivities (typically >95:5 er) under sequential catalysis that integrates alkene cross-metathesis, isomerization, and nucleophilic addition. Prochiral allylic alcohols can be converted to any stereoisomer of the product with high stereoselectivity (>98:2 er, >20:1 dr).

Full text of DOI:10.1021/acs.orglett.1c00939

pubs.acs.org/OrgLett
Letter
Multicatalytic Approach to One-Pot Stereoselective Synthesis of
Secondary Benzylic Alcohols
Alessandra Casnati,‡ Dawid Lichosyt,‡ Bruno Lainer, Lukas Veth, and Paweł Dydio*
Cite This: Org. Lett. 2021, 23, 3502−3506
Read Online
sı
*
Metrics & More
Article Recommendations
Supporting Information
ACCESS
ABSTRACT: One-pot procedures bear the potential to rapidly
build up molecular complexity without isolation and purification of
consecutive intermediates. Here, we report multicatalytic protocols
that convert alkenes, unsaturated aliphatic alcohols, and aryl
boronic acids into secondary benzylic alcohols with high
stereoselectivities (typically >95:5 er) under sequential catalysis
that integrates alkene cross-metathesis, isomerization, and
nucleophilic addition. Prochiral allylic alcohols can be converted
to any stereoisomer of the product with high stereoselectivity
(>98:2 er, >20:1 dr).
econdary benzylic alcohols (SBAs) represent prevalent
motifs of biologically active molecules and chiral building
fashion, without or with limited intermediary workup, proved
enabling and highly advantageous from the efficiency stand-
point.15,16 However, the development of such protocols with
multiple transition-metal-catalyzed reactions operating in one
vessel remains challenging.17 The prospective cross-reactivity is
likely to hinder the required activity.18 In asymmetric
reactions, any exchange of ligands is likely to deteriorate the
stereoselectivity.19 Therefore, careful selection of catalysts and
conditions is critical.
Here, we report sequential multistep protocols with up to
three transition-metal complexes and a Brønsted acid that
execute redox-neutral transformations for a series of alkenes,
(protected) unsaturated alcohols, and aryl boronic acids, with
no or with minimal intermediary workup, to furnish varied
SBAs in high stereoselectivity, with up to 99:1 er, dr >20:1, and
91% yield (Figure 1f−h). We showed that not only the
protocols are operationally simpler and up to ∼3-fold less
resource-intensive than the stepwise synthesis but also that the
overall yield of the product is increased (77% versus 43%)
thanks to preventing cumulative losses of the materials during
subsequent isolations and purifications of the intermediates.
We initiated the study by validating the possibility to
conduct in situ both the isomerization of unsaturated alcohols
and the addition of aryl boronic acids to aldehyde
S
blocks for fine-chemical synthesis. Therefore, methods for their
stereoselective synthesis from available starting materials are
important. Asymmetric (transfer) hydrogenation proved highly
effective when aryl ketones are available (Figure 1a).1 In turn,
enantioselective addition of an aryl nucleophile to a carbonyl
bond is practical for aliphatic aldehydes as starting materials
(Figure 1b).2,3 Given the abundance of alcohols, functionaliza-
tion of their C−H bonds is attractive.4−6 In that regard,
Krische reported an elegant enantio- and diastereoselective α-
alkylation of alcohols with unsaturated hydrocarbons (e.g.,
dienes, enynes; Figure 1c).7 Methods for α-arylation of
aliphatic alcohols were recently reported by MacMillan, Lei,
and Shirakawa (Figure 1d),8−10 although the enantioselective
variants remain to be developed. In addition, the stereo-
retentive cross-couplings to form SBAs were reported by Falck
and Molander (Figure 1e).11,12
We envisioned that one-pot sequential catalysis could enrich
the access to SBAs from other classes of readily available
starting materials (Figure 1f−h). First, we conceived the
enantioselective isomerization−addition sequence for aliphatic
alcohols bearing an unsaturated bond (Figure 1f), which are
common motifs in bioderived materials (e.g., terpenols). The
strategy could be further extended to abundant alkenes (Figure
1g), given the alkene cross-metathesis,13 double-bond isomer-
ization,14 and enantioselective addition2,3 reactions were
compatible in a one-pot fashion. Also, diastereoselective
synthesis of SBAs bearing two stereocenters with a 1,3-
relationship could be envisioned (Figure 1h), provided the
compatibility of both chiral catalysts was ensured. Noteworthy,
the execution of multicatalytic multistep synthesis in a one-pot
Received: March 18, 2021
Published: April 12, 2021
https://doi.org/10.1021/acs.orglett.1c00939
© 2021 American Chemical Society
Org. Lett. 2021, 23, 3502−3506
3502

Organic Letters
pubs.acs.org/OrgLett
Letter
Figure 1. Context and the current study: stereoselective synthesis of
secondary benzylic alcohols (SBAs).
Figure 2. Studies toward the enantioselective conversion of allylic
alcohols to SBAs. (a) By NMR, GC, or SFC analysis. (b) A mixture of
1a and Ir-1 was kept at 30 °C for 2 h, followed by the addition of 2a
and (R,R)-Ru-1 (6.0 mol %), and kept at 60 °C for 6 h. (c) 0.125 mol
% Ir-1. (d) Yield of isolated material.
intermediates. Model substrates, trans-2-hexenol 1a and
phenylboronic acid 2a, reacted to furnish racemic alcohol
3aa, 1-phenyl-1-hexanol in 84% yield in the presence of
[Ir(cod)Cl]2 (Ir-1), and [Rh(cod)(CH3CN)2]BF4 (Rh-1)
(Figure 2a). The control experiments confirmed the role of
both complexes. The reactivity was diminished when either
complex was not present.
addition of 2a and (R,R)-Ru-1, (R)-3aa was formed in 81%
yield (78% isolated material) and 96:4 er.
The enantioselective variant of the transformation required
exchanging the Rh-catalyst for the Ru-complex bearing chiral
Me-BIPAM (Ru-1, Figure 2b), the latter being a privileged
ligand developed by Yamamoto and Miyaura for enantiose-
lective Rh- or Ru-catalyzed reactions, including 1,2-addition
reactions.20,21 We found that although a Rh-catalyst bearing
chiral diene ligand Rh-2/cod*3 proved active, product 3aa was
formed in modest enantioselectivity (70:30 er). The evaluation
of other Rh-complexes bearing N-sulfinyl chiral sulfur-olefin22
Rh-2/sulpho or phosphine2 Rh-2/BINAP ligands, did not
secure any highly enantioselective protocol. In sharp contrast,
the reaction in the presence of Ir-1 and (R,R)-Ru-2,21
furnished product (R)-3aa in high er of 96:4, albeit in a low
yield of 23%. The use of other isomerization catalysts14 in
place of Ir-1 enabled the formation of (R)-3aa in higher yields.
The reaction in the presence of Ru-4 and (R,R)-Ru-1
furnished the product in 55% yield and 96:4 er. Further
experiments revealed that the presence of Ru-1 partially
inhibits the activity of Ir-1. Fortunately, when 1a was shortly
incubated in the presence of 0.125 mol % Ir-1, prior to the
The identified protocol proved applicable to a substantial
range of aryl boronic acids and alkenylic alcohols (Figure 3).
The reactions of 1a with phenylboronic acid derivatives
containing an electron-donating or an electron-withdrawing
group in the para- or meta-position of the phenyl ring (2b−2i,
2k−2n) as well as those with a sizable aryl moiety (2o−2q)
formed the product with 92:8 to 99:1 er and up to 86% yield.
The reactions for aryl boronic acids bearing either a strongly
electron-withdrawing group or steric hindrance in the ortho-
position, such as 2j and 2r−2t, respectively, furnished the
products in modest yields (up to 31%) and moderate
enantioselectivity (<79:21 er), indicating the limitations of
the protocol. Heteroaryl derivatives, including dibenzothio-
phene 2o and 1,3-benzodioxole 2p, reacted to form the
products in 95:5 er and 33−60% yields. Alcohols containing a
remote double bond, such as homoallylic 3-hexenol 1b and 5-
hexenol 1c, are suitable substrates; however, the Zipper
catalyst Ru-323 was used in place of Ir-1 to form the products
in high yields (93% and 90%, respectively). It is worth noting
3503
https://doi.org/10.1021/acs.orglett.1c00939
Org. Lett. 2021, 23, 3502−3506

Organic Letters
pubs.acs.org/OrgLett
Letter
M721(Ru-5) followed in situ by the isomerization−addition
sequence with 2a, Ru-2, and (R,R)-Ru-1 furnished benzylic
alcohol (R)-6aa in 98:2 er (Figure 4). High stereoselectivity of
Figure 4. Enantioselective sequential multicatalysis for conversion of
alkenes to SBAs. (a) As in Figure 3; no workup except for washing off
TFA and optional drying over Na2SO4; (b) With cis-2-butene-1,4-
diol.
Figure 3. Scope for conversion of linear alkenylic alcohols to SBAs.
(a) Reagents added to the mixture subsequently without any workup;
yields of isolated material are reported (yields determined by NMR
analysis are ∼2−13% higher; see the SI); er calculated by SFC
analysis. (b) Second step at 90 °C for 24 h. (c) Yields by NMR
analysis using an internal standard. (d) Ru-2 (2 mol %).
the reaction confirmed the critical compatibility of chiral Ru-1
with the other catalysts in the sequence. However, because of
the limited conversion of alkene 4a to allylic alcohol
intermediate 7, product (R)-6aa was formed in only up to
11% yield (Tables S1 and S2). Alkene 4a reacted more readily
with 5′, TMS-protected 5, in the presence of Ru-5, forming 7′
in a high yield (>95% by GC analysis). The latter was quickly
and quantitatively deprotected to form alkenol 7 in the
presence of trifluoroacetic acid. The acid was washed off with
an aqueous base solution, and no further workup is required
for the subsequent isomerization−addition sequence. How-
ever, because the full removal of aqueous phase is essential, we
noticed that drying the reaction mixture over Na2SO4 (and its
removal) prior to the subsequent steps is beneficial for the
reproducibility. Overall, such protocol that engages three
different Ru-catalysts and a Brønsted acid with a minimal
intermediary workup converts 4a, 5′, and 2a to alcohol (R)-
6aa in 88% yield (79% isolated material) and 98:2 er.
that the presence of Ru-3 bearing an achiral phosphine ligand
does not erode the enantioselectivity of the step executed by
Ru-1 (96:4 er), demonstrating the key compatibility between
the catalysts.
Because cross-metathesis represents a convenient method to
install an alkenylic alcohol moiety on olefins, we next sought a
protocol that would enable the direct assembly of a SBA from
an alkene, a simple alkenylic alcohol, and an aryl boronic acid.
Such method would be attractive due to the increase in the
structural diversity of the products by using combinations of
readily accessible building blocks. However, the requirement of
the compatibility of three transition-metal catalysts in the series
of three subsequent processes represents a challenge. Cross-
inhibition issues aside, any ligand-exchange processes between
a metathesis or an isomerization catalyst and a chiral catalyst
that operates in the final 1,2-addition step are likely to
deteriorate the stereoselectivity.
The side-by-side experiments on a 2.4 mmol scale of 4a for
the synthesis of (R)-6aa proved that not only the established
protocol is faster, more operationally simple, and ∼3-fold less
resource-intensive than the stepwise approach, but also the
final yield of the isolated material is increased, i.e., 77% versus
43%, respectively. Although the consecutive steps of the
sequence occurred with similar GC yields in both cases, the
Initial experiments indicated that a cross-metathesis reaction
of 4,4-dimethyl-1-pentene (4a) and cis-2-butene-1,4-diol (5) in
the presence of the o-tolyl Hoveyda−Grubbs catalyst
3504
https://doi.org/10.1021/acs.orglett.1c00939
Org. Lett. 2021, 23, 3502−3506

Organic Letters
pubs.acs.org/OrgLett
Letter
sequential protocol prevented cumulative losses of the material
during subsequent isolations and purifications of the
intermediates, illustrating an additional advantage of the
approach (for details, see Tables S3 and S4).
The established protocol integrating alkene cross-metathesis,
isomerization, and enantioselective addition is broadly
applicable (Figure 4). A series of aliphatic alkenes, electron-
rich or electron-deficient vinyl arenes, TMS-protected alkenol,
and stereoelectronically varied aryl boronic acids reacted to
form a range of SBAs in high enantioselectivities (er’s > 95:5)
and 48−87% yields (isolated material).
Lastly, we focused on allylic alcohols bearing a prochiral
double bond. The isomerization−addition sequence for 3-
substituted allylic alcohols constitutes an attractive strategy to
produce the SBAs bearing two stereocenters with a 1,3-
relationship. We surmised that a method utilizing two different
chiral catalysts that independently construct each stereogenic
center would give access to all 1,3-syn and 1,3-anti stereo-
isomers of the product. However, the key requirement is the
independent activity of both chiral catalysts and their
compatibility.
Combining suitable enantiomers of Ru-3, the isomerization
catalyst reported by Ohkuma,24 and Ru-1 enables the
isomerization−addition sequence to form different diaster-
eomers of the products with high stereocontrol in a one-pot
fashion (Figure 5). The catalysts proved to require different
solvents to operate efficiently (i.e., ethanol and toluene,
respectively; for details, see Figures S1−S4 and Table S5).
Therefore, the medium needs to be exchanged between the
steps (evaporation under vacuum); albeit no resource-intensive
workup is needed. Importantly, the stereocontrol for the
formation of each stereogenic center is solely determined by
the catalyst involved. For instance, while the reaction of
geraniol 8a and 2a in the presence of (S)-Ru-3 and (S,S)-Ru-1
furnished 1,3-syn benzylic alcohol (1S,3R)-9aa with >99:1 er,
>20:1 dr, in 62% yield, the same reaction but with (R,R)-Ru-1
in place of (S,S)-Ru-1 furnished 1,3-anti diastereomeric
alcohol (1S,3S)-9aa′, in similarly high 99:1 er, >20:1 dr, and
61% yield. The diastereoselectivity of the transformation
depends on the configuration of the double bond in the
starting material.24 Under the conditions that geraniol 8a
reacted to from 1,3-syn 9aa, nerol 8b, the (Z)-analogue of
geraniol 8a, reacted to form 1,3-anti 9ba′ containing the
opposite major enantiomer of 9aa′, in 99:1 er, > 20:1 dr, and
60% yield. Noteworthy, the isolated double bonds of starting
materials 8a−8b remained intact in the corresponding
products. Chiral phytol 8c, reacted with varied arylboronic
acids to form the products in high stereoselectivity, i.e., 90−
97% of the major stereoisomer, and from 43% to 70% yield.
The presence of an additional chiral center next to the allylic
alcohol moiety in the starting material seems not to disturb the
reaction. (+)-Limonene derivative 8d reacted with 2a to form
9da in >20:1 dr, and 41% yield, expanding the scope of the
system.
Figure 5. Stereoselective conversion of substitute allylic alcohols to
SBAs. (a) As in Figure 2; no workup except for removal of EtOH
under vacuum; yields of the isolated major diastereomer. (b) dr of
1,3-syn (major):1,3-syn(minor):sum of 1,3-anti products.
synthesis of target motifs, increases material efficiency, and
limits cost, time, and waste associated with the standard
stepwise procedures. In a greater perspective, the study
highlights the synthetic potential of the multicatalytic
approaches to quickly access increasingly complex architec-
tures from simple starting materials.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.1c00939.
In conclusion, the herein disclosed methods enable the rapid
modular stereoselective syntheses of a broad range of
secondary benzylic alcohols from simple available starting
materials.25 The strategy relies on the construction of the
sequences of multiple catalytic reactions occurring consec-
utively with no or minimal intermediary workup. The
transformation is executed with the aid of up to three
transition-metal catalysts and requires a single isolation and
purification of the product. Overall, the approach simplifies the
Experimental details and data (PDF)
AUTHOR INFORMATION
■
Corresponding Author
Paweł Dydio − University of Strasbourg, CNRS, ISIS UMR
7006, 67000 Strasbourg, France; orcid.org/0000-0001-
5095-4943; Email: dydio@unistra.fr
3505
https://doi.org/10.1021/acs.orglett.1c00939
Org. Lett. 2021, 23, 3502−3506

Organic Letters
Authors
pubs.acs.org/OrgLett
Letter
(10) Aoki, K.; Yonekura, K.; Ikeda, Y.; Ueno, R.; Shirakawa, E.
Direct a-Arylation of Alcohols with Aryl Halides through a Radical
Chain Mechanism. Adv. Synth. Catal. 2020, 362 (11), 2200−2204.
(11) Goli, M.; He, A.; Falck, J. R. Pd-Catalyzed Cross-Coupling of
α-(Acyloxy)-Tri- n -Butylstannanes with Alkenyl, Aryl, and Heteroaryl
Electrophiles. Org. Lett. 2011, 13 (2), 344−346.
(12) Molander, G. A.; Wisniewski, S. R. Stereospecific Cross-
Coupling of Secondary Organotrifluoroborates: Potassium 1-
(Benzyloxy)Alkyltrifluoroborates. J. Am. Chem. Soc. 2012, 134 (40),
16856−16868.
(13) Xu, C.; Liu, Z.; Torker, S.; Shen, X.; Xu, D.; Hoveyda, A. H.
Synthesis of Z - or E -Trisubstituted Allylic Alcohols and Ethers by
Kinetically Controlled Cross-Metathesis with a Ru Catechothiolate
Complex. J. Am. Chem. Soc. 2017, 139 (44), 15640−15643. See also
references cited therein.
(14) Fiorito, D.; Scaringi, S.; Mazet, C. Transition Metal-Catalyzed
Alkene Isomerization as an Enabling Technology in Tandem,
Sequential and Domino Processes. Chem. Soc. Rev. 2021, 50 (2),
1391−1406. See also references cited therein.
(15) Hayashi, Y. Pot Economy and One-Pot Synthesis. Chem. Sci.
2016, 7 (2), 866−880.
Alessandra Casnati − University of Strasbourg, CNRS, ISIS
UMR 7006, 67000 Strasbourg, France
Dawid Lichosyt − University of Strasbourg, CNRS, ISIS UMR
7006, 67000 Strasbourg, France
Bruno Lainer − University of Strasbourg, CNRS, ISIS UMR
7006, 67000 Strasbourg, France
Lukas Veth − University of Strasbourg, CNRS, ISIS UMR
7006, 67000 Strasbourg, France
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.1c00939
Author Contributions
‡A.C. and D.L. contributed equally.
Notes
The authors declare no competing financial interest.
(16) Yadav, R. N.; Srivastava, A. K.; Banik, B. K. One-Pot Strategy: A
Highly Economical Tool in Organic Synthesis and Medicinal
Chemistry. In Green Approaches in Medicinal Chemistry for Sustainable
Drug Design; Elsevier, 2020; pp 353−425. DOI: 10.1016/B978-0-12-
817592-7.00010-1.
(17) Sancheti, S. P.; Urvashi; Shah, M. P.; Patil, N. T. Ternary
Catalysis: A Stepping Stone toward Multicatalysis. ACS Catal. 2020,
10 (5), 3462−3489. See also references cited therein.
(18) Martínez, S.; Veth, L.; Lainer, B.; Dydio, P. Challenges and
Opportunities in Multicatalysis. ACS Catal. 2021, 11, 3891−3915.
See also references cited therein.
(19) Pellissier, H. Recent Developments in Enantioselective
Multicatalyzed Tandem Reactions. Adv. Synth. Catal. 2020, 362
(12), 2289−2325. See also references cited therein.
(20) Yamamoto, Y.; Kurihara, K.; Miyaura, N. Me-Bipam for
Enantioselective Ruthenium(II)-Catalyzed Arylation of Aldehydes
with Arylboronic Acids. Angew. Chem., Int. Ed. 2009, 48 (24), 4414−
4416.
(21) Yamamoto, Y.; Shirai, T.; Watanabe, M.; Kurihara, K.; Miyaura,
N. Ru/Me-BIPAM-Catalyzed Asymmetric Addition of Arylboronic
Acids to Aliphatic Aldehydes and α-Ketoesters. Molecules 2011, 16
(6), 5020−5034.
(22) Zhu, T.-S.; Jin, S.-S.; Xu, M.-H. Rhodium-Catalyzed, Highly
Enantioselective 1,2-Addition of Aryl Boronic Acids to α-Ketoesters
and α-Diketones Using Simple, Chiral Sulfur-Olefin Ligands. Angew.
Chem., Int. Ed. 2012, 51 (3), 780−783.
(23) Grotjahn, D. B.; Larsen, C. R.; Gustafson, J. L.; Nair, R.;
Sharma, A. Extensive Isomerization of Alkenes Using a Bifunctional
Catalyst: An Alkene Zipper. J. Am. Chem. Soc. 2007, 129 (31), 9592−
9593.
(24) Arai, N.; Sato, K.; Azuma, K.; Ohkuma, T. Enantioselective
Isomerization of Primary Allylic Alcohols into Chiral Aldehydes with
the Tol-Binap/Dbapen/Ruthenium(II) Catalyst. Angew. Chem., Int.
Ed. 2013, 52 (29), 7500−7504.
ACKNOWLEDGMENTS
■
We acknowledge funding from the European Research Council
(ERC StG no 804106), the French National Research Agency
(ANR IdEx, ANR LabEx, “Chemistry of Complex Systems”,
and a PhD fellowship for B.L. under contract 17-EURE-0016).
We are thankful to K. Hurej (University of Strasbourg) for
preliminary experiments and D. Leboeuf (University of
Strasbourg) for the comments on the manuscript.
DEDICATION
■
We dedicate this paper to Prof. Janusz Jurczak (Polish
Academy of Sciences) on the occasion of his 80th birthday.
REFERENCES
■
(1) Seo, C. S. G.; Morris, R. H. Catalytic Homogeneous Asymmetric
Hydrogenation: Successes and Opportunities. Organometallics 2019,
38 (1), 47−65.
(2) Tian, P.; Dong, H.-Q.; Lin, G.-Q. Rhodium-Catalyzed
Asymmetric Arylation. ACS Catal. 2012, 2 (1), 95−119.
(3) Defieber, C.; Grutzmacher, H.; Carreira, E. M. Chiral Olefins as
̈
Steering Ligands in Asymmetric Catalysis. Angew. Chem., Int. Ed.
2008, 47 (24), 4482−4502.
(4) Mo, F.; Tabor, J. R.; Dong, G. Alcohols or Masked Alcohols as
Directing Groups for C−H Bond Functionalization. Chem. Lett. 2014,
43 (3), 264−271. See also references cited therein.
(5) Nguyen, K. D.; Park, B. Y.; Luong, T.; Sato, H.; Garza, V. J.;
Krische, M. J. Metal-Catalyzed Reductive Coupling of Olefin-Derived
Nucleophiles: Reinventing Carbonyl Addition. Science 2016, 354
(6310), aah5133.
(6) Lichosyt, D.; Zhang, Y.; Hurej, K.; Dydio, P. Dual-Catalytic
Transition Metal Systems for Functionalization of Unreactive Sites of
Molecules. Nat. Catal. 2019, 2 (2), 114−122.
(7) Kim, S. W.; Zhang, W.; Krische, M. J. Catalytic Enantioselective
Carbonyl Allylation and Propargylation via Alcohol-Mediated Hydro-
gen Transfer: Merging the Chemistry of Grignard and Sabatier. Acc.
Chem. Res. 2017, 50 (9), 2371−2380. See also references cited
therein.
(25) Casnati, A.; Lichosyt, D.; Lainer, B.; Veth, L.; Dydio, P. Multi-
Catalytic Approach to One-Pot Stereoselective Synthesis of
Secondary Benzylic Alcohols. ChemRxiv 2021, DOI: 10.26434/
chemrxiv.14115551.v1.
(8) Twilton, J.; Christensen, M.; DiRocco, D. A.; Ruck, R. T.;
Davies, I. W.; MacMillan, D. W. C. Selective Hydrogen Atom
Abstraction through Induced Bond Polarization: Direct α-Arylation of
Alcohols through Photoredox, HAT, and Nickel Catalysis. Angew.
Chem., Int. Ed. 2018, 57 (19), 5369−5373.
(9) Niu, L.; Liu, J.; Liang, X.-A.; Wang, S.; Lei, A. Visible Light-
Induced Direct α C−H Functionalization of Alcohols. Nat. Commun.
2019, 10 (2), 467 DOI: 10.1038/s41467-019-08413-9.
3506
https://doi.org/10.1021/acs.orglett.1c00939
Org. Lett. 2021, 23, 3502−3506