Asymmetric synthesis of 1,2-fluorohydrin: Iridium catalyzed hydrogenation of fluorinated allylic alcohol

Article abstract of DOI:10.1039/d0sc04032k

We have developed a simple protocol for the preparation of 1,2-fluorohydrin by asymmetric hydrogenation of fluorinated allylic alcohols using an efficient azabicyclo thiazole-phosphine iridium complex. The iridium-catalyzed asymmetric synthesis of chiral 1,2-fluorohydrin molecules was carried out at ambient temperature with operational simplicity, and scalability. This method was compatible with various aromatic, aliphatic, and heterocyclic fluorinated compounds as well as a variety of polyfluorinated compounds, providing the corresponding products in excellent yields and enantioselectivities. This journal is

Full text of DOI:10.1039/d0sc04032k

Chemical
Science
View Article Online
View Journal
EDGE ARTICLE
Asymmetric synthesis of 1,2-fluorohydrin: iridium
catalyzed hydrogenation of fluorinated allylic
Cite this: DOI: 10.1039/d0sc04032k
alcohol†
Sudipta Ponra,‡a Jianping Yang, ‡a Haibo Wu,
All publication charges for this article
have been paid for by the Royal Society
of Chemistry
a
Wangchuk Rabtena
ab
*
and Pher G. Andersson
We have developed a simple protocol for the preparation of 1,2-fluorohydrin by asymmetric hydrogenation
of fluorinated allylic alcohols using an efficient azabicyclo thiazole-phosphine iridium complex. The
iridium-catalyzed asymmetric synthesis of chiral 1,2-fluorohydrin molecules was carried out at ambient
temperature with operational simplicity, and scalability. This method was compatible with various
aromatic, aliphatic, and heterocyclic fluorinated compounds as well as a variety of polyfluorinated
compounds, providing the corresponding products in excellent yields and enantioselectivities.
Received 23rd July 2020
Accepted 24th August 2020
DOI: 10.1039/d0sc04032k
rsc.li/chemical-science
particularly notable.3b,8 Many of the existing methods for the
synthesis of stereoselective uorohydrins have economical or
Introduction
practical setbacks, oen relating to the uorinating agents. The
lack of general atom economical asymmetric process
Despite the limited number of uorinated natural products, the
introduction of a uorine atom into an organic molecule can
have an immense impact in small molecule drug discovery.1
Moreover, the stereocontrolled introduction of uorine atoms
into organic molecules can be expected to be the next chapter
for the development of drugs possessing excellent bioactivity
and bioavailability.1b,c,e,2 However, current synthetic methodol-
ogies lack a waste-free and easy stereoselective approach for the
construction of complex bioactive uorinated molecules. Fluo-
rohydrins3 are well-known as an important subclass of orga-
nouorine compounds. They serve as key intermediates in the
synthesis of mono-uorinated analogues for many bioactive
compounds.4 They are also used as derivatizing agents in
determining enantiomeric composition by 19F NMR spectros-
copy.5 Classic examples of drug molecules containing the 1,2-
uorohydrin substructure are udrocortisone (the rst uorine-
containing marketed drug);6 anti-inammatory corticosteroid
diuprednate7a–c and antihepatitis C agent sofosbuvir.7d Along
with steroid and nucleotide analogs a few alkaloid-derived u-
orohydrins have also been reported.7e Nucleophilic opening of
epoxides with various uoride sources are one of the most
reliable methods for uorohydrin synthesis. The use of HF-
based reagents (e.g., Olah's reagent) as a uoride source is
a
prompted us to devise a highly enantioselective synthetic
method for the versatile generation of uorohydrin molecules.
The asymmetric hydrogenation of olens using iridium
complexes without a coordinating group or a weakly coordinating
group is one of the most fundamental and atom economical
processes in synthetic organic chemistry.9 For the trisubstituted
olens, the smallest substituent, which is hydrogen, determines
which enantioface of the olen preferentially coordinates to the Ir
center. Since, H and F are both small substituents and almost of
similar size, there is more than one possible orientation of the
olen for trisubstituted uorinated allylic alcohols. This presents
a signicant challenge since it results in enantiomeric mixtures
of the hydrogenated product.10 Selectivity together with the
frequent occurrence of deuorination (de-F) during hydrogena-
tion and the electron-withdrawing property of uorine makes
trisubstituted uorinated olens an even more difficult substrate
for hydrogenation.11 Since olens are inexpensive and widely
available it led us to investigate the asymmetric hydrogenation of
uorinated allylic alcohols as a possible method to produce bio-
relevant uorohydrin compounds.12 Recently, we reported the
successful development of an efficient catalytic system for the
enantioselective synthesis of uorine motifs based on the highly
selective hydrogenation of alkenyl uorides.10,12d,g Our Ir-N,P
a
¨
Department of Organic Chemistry, Stockholm University, Svante Arrhenius vag 16C,
SE-10691 Stockholm, Sweden. E-mail: Pher.Andersson@su.se
bSchool of Chemistry and Physics, University of KwaZulu-Natal, Private Bag X54001,
Durban, 4000, South Africa
† Electronic supplementary information (ESI) available: Experimental procedures,
crystallography reports, and analytical data (PDF). CCDC 1976216 crystallographic
data for 2n (CIF). For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/d0sc04032k
Scheme
1
Atom economical synthesis of asymmetric 1,2-
‡ Authors contributed equally to this work.
fluorohydrin.
This journal is © The Royal Society of Chemistry 2020
Chem. Sci.

View Article Online
Chemical Science
Edge Article
catalyst was moderately successful for the asymmetric synthesis as the model substrate and bicyclic oxazoline-o-Et-
of uorohydrins by hydrogenation, however it was limited to phenylphosphine iridium complex12a A as the catalyst using
specic substrates12a or gave poor enantioselectivity with a high the following reaction conditions: 1 mol% catalyst, CH2Cl2, and
extent of de-F.12b With these limitations in mind, we set out to 10 bar H2. Substrate 1a gave 99% conversion of the starting
develop an efficient catalytic system for the atom economical material along with slight de-F (4%) and very good enantiose-
asymmetric synthesis of uorohydrins by hydrogenation of lectivity (87% ee) (Table 1). Catalysts having a thiazole backbone
uorinated allylic alcohols (Scheme 1).
(catalyst B and catalyst C) led to an improved enantioselectivity
of 96% ee with very minute de-F (1–2%). Further optimization of
the heterocycle skeleton of the N,P-iridium complex involved
changing thiazole to imidazole (catalyst D) which provided
a comparable result but with 10% de-F. Catalyst E which was
superior in our previous study12a on asymmetric hydrogenation
of uorinated allylic alcohol gave 97% ee with 2% de-F (more
details, see: ESI†). We nally evaluated the effect of the
substituent on phosphorous and replaced the two cyclohexyl
groups with ortho-tolyl groups (catalyst F) and obtained the best
result for 1a: 99% conversion with excellent enantioselectivity
(97%) and <1% of the de-F by-product.
Results and discussion
For the asymmetric hydrogenation investigation reported here,
we selected (Z)-2-uoro-3-(4-methoxyphenyl)prop-2-en-1-ol (1a)
Table
1 Evaluation of N,P-iridium catalysts in the asymmetric
hydrogenation of 1aa
Having successfully found a new effective catalyst containing
a bicyclic thiazole backbone with o-tolyl substituents on phos-
phorus F, we carried out further optimization of the solvent,
catalyst loading and hydrogen pressure (Table 2). Solvent
screening with CH2Cl2, DCE and PhCF3 proved that CH2Cl2 was
the best in terms of reactivity, enantioselectivity and de-
uorination. When the H2 pressure decreased from 10 bar
(entry 1) to 4 bar (entry 4) using 1.0 mol% of catalyst F for 24
hours, conversion was not affected but de-F increased slightly to
2%. A decrease in the catalyst loading at 10 bar of H2 pressure
for substrate 1a from 1.0 mol% (entry 1) to 0.5 mol% (entry 5)
also increased the de-F to 4%. Hence, for substrate 1a the
optimal conditions for full conversion, good enantioselectivity
and minimal de-F are a catalyst loading of 1.0 mol% (catalyst F)
and 10 bar H2 pressure for 24 hours (entry 1). It should be noted
that almost no de-F product (<1%) was observed as a side
reaction which is a recurring problem in hydrogenations of
alkenyl uorides.11b
With the optimized reaction conditions established, we eval-
uated the hydrogenation of variously substituted (Z)-2-uoro-3-
phenylprop-2-en-1-ols 1 (Table 3). A variety of uorinated allylic
a
Reaction conditions: 0.05 mmol of 1a, 1 mol% catalyst, 0.5 mL CH2Cl2,
10 bar H2. Conversion was determined by 1H-NMR spectroscopy.
Enantiomeric excess was determined by SFC.
Table 2 Optimization of hydrogenation of vinyl fluoride 1aa
Entry
Solvent
H2 (bar)
Catalyst (mol%)
Conversion (%)
de-F (%)
ee (%)
1
2
3
4
5
CH2Cl2
DCE
PhCF3
CH2Cl2
CH2Cl2
10
10
10
4
1.0
1.0
1.0
1.0
0.5
99
99
98
99
99
<1
3
3
2
4
97
97
97
97
97
10
a
Reaction conditions: 0.05 mmol of 1a, 0.5 mL solvent. Conversion was determined by 1H-NMR spectroscopy. Enantiomeric excess was determined
by SFC.
Chem. Sci.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Edge Article
Chemical Science
Table 3 Hydrogenation of various fluorinated allylic alcoholsa
Table 4 Hydrogenation of various polyfluorinated allylic alcoholsa
a
Reaction conditions: 0.25 mmol of substrate, 1 mol% of catalyst ent-F,
a
2.0 mL CH2Cl2. Yields are isolated hydrogenated product. Enantiomeric
excess was determined by SFC or GC/MS using chiral stationary phases.
Reaction conditions: 0.25 mmol of substrate, 1 mol% catalyst, 2.0 mL
b
c
CH2Cl2. Catalyst F. Catalyst ent-F. Yields are isolated hydrogenated
product. Enantiomeric excess was determined by SFC or GC/MS using
chiral stationary phases.
Notably, this method was amenable for (Z)-3-uorooct-2-en-
alcohols were successfully hydrogenated to generate the desired 1-ol 1y. The hydrogenated product 2y was obtained in good ee
products 2a–2e in excellent yields and enantioselectivities. The (83%), where the chiral center containing uorine is at the
(Z)-2-uoro-3-phenylprop-2-en-1-ol substrates with either b position to the CH2OH group (Scheme 2).
electron-donating or electron-withdrawing substituents at the
A preparative-scale production of chiral uorohydrin under
para or ortho position of the aryl rings provided the desired these reaction conditions was also carried out. Starting with
products in high isolated yields (96–99%) and excellent enan- 1.0 g of allylic alcohol 1c and using 0.5 mol% of catalyst F under
tioselectivities (93–97% ee). Replacing the phenyl group with 2- 10 bar H2, the desired uorohydrin 2c was obtained in excellent
naphthyl or a heterocyclic (thienyl) substituent also yielded the 97% yield with 97% ee (Scheme 3).
desired products (2f–2h) in excellent yields (95–98%) and ees (96–
98%). Next, we examined the secondary and tertiary vinyl-F
Table 5 Hydrogenation of various aliphatic fluorinated allylic
alcoholsa
alcohols and as expected, all gave satisfactory results. Again,
very low de-F (0–12%) was observed in all examples, which
underlines the effectiveness of this catalytic method.
Since de-F during hydrogenation of alkenyl uorides pres-
ents potential challenges,11 various polyuorinated allylic alco-
hols were hydrogenated under standard conditions (Table 4).
For all examples, irrespective of the position of the uorine or
the triuoromethyl substituent on the aromatic ring, we
observed only traces of de-F products (0–9%) along with high
yields (70–99%) and enantioselectivities (95–>99% ee) for the
polyuorinated 1,2-uorohydrins.
The efficacy of this stereoselective 1,2-uorohydrin synthesis
was investigated by evaluating various aliphatic uorinated
allylic alcohols (Table 5). Gratifyingly, a number of aliphatic
uorinated allylic alcohols (1s–1x) were also efficiently hydro-
genated in good to excellent yields (71–99%) with high enan-
tioselectivities (71–92% ee). Interestingly, both isomers (E & Z)
of 2-uoro-4-phenylbut-2-en-1-ol were hydrogenated with
excellent results. Various acyclic and cyclic primary, secondary,
and tertiary aliphatic substituents afforded the anticipated
product (2s–2x) without generating any problematic de-F.
a
Reaction conditions: 0.25 mmol of substrate, 1 mol% catalyst F,
2.0 mL CH2Cl2. Yields are isolated hydrogenated product.
Enantiomeric excess was determined by HPLC or GC/MS using chiral
stationary phases.
This journal is © The Royal Society of Chemistry 2020
Chem. Sci.

View Article Online
Chemical Science
Edge Article
Table 6 Hydrogenation of fluorinated allylic acetatesa
Scheme 2 Hydrogenation of (Z)-3-fluorooct-2-en-1-ol.
a
Reaction conditions: 0.25 mmol of substrate, 1 mol% catalyst, 2.0 mL
b
c
CH2Cl2. Catalyst F. Catalyst ent-F. Yields are isolated hydrogenated
product. Enantiomeric excess was determined by SFC or GC/MS using
chiral stationary phases.
Scheme 3 Gram-scale production of chiral fluorohydrin.
The enantioenriched 1,2-uorohydrins can be transformed
into a variety of many useful chiral uorinated derivatives: acid
4, aldehyde 5, and sulfamate 6 were all obtained without any
loss in enantiopurity (Scheme 4). The synthetic intermediate (S)-
2-uoro-3-phenylpropyl sulfamate 6 could be a potential key
precursor for the synthesis of dapoxetine13 analogs, a useful
selective serotonin reuptake inhibitor (SSRI).
The Ir-complex (F) having the bicyclic thiazole backbone
with o-tolyl substituents on phosphorus was also effective for
uorinated allylic acetates (8a–8c) (Table 6), giving good yields
(40–72%) and enantioselectivities (93–94% ee), although at
a higher level of deuorination.
Steric interactions between the olen and the N,P-iridium
catalyst controls the enantioselectivity of iridium-catalyzed
asymmetric hydrogenations.14,15 A quadrant model was devel-
oped14 using catalyst F to explain the enantioselectivity and is
similar to our earlier observations.10 The Ir-N,P ligand (F) was
positioned as depicted in Scheme 5a, with the iridium atom at
the center of the four quadrants (Scheme 5b). The olen (uo-
rinated allylic alcohol) coordinates vertically trans to phos-
phorus (Scheme 5c). The phenyl group on the thiazole moiety
points outwards, making quadrant iii sterically hindered. One
of the o-tolyl groups on the phosphorus atom also points
slightly outwards, making quadrant ii the semi-hindered
quadrant. Since quadrants i and iv do not experience obstruc-
tions from the ligand, they are considered open quadrants.
When the trisubstituted (Z)-uoro alcohol 1c is placed trans to
phosphorus, such that the smallest substituent (H) occupies the
hindered quadrant iii and the other small substituent (F)
occupies the semi-hindered quadrant ii, this results in a favored
arrangement (Scheme 5d). Since the H and F atoms are of
similar size, another sterically favorable possible arrangement
is to place uorine in the sterically hindered quadrant iii
(Scheme 5e). The two other possible arrangements are sterically
not favored (Scheme 5f and g). Thus, based on the quadrant
model, both sterically favored orientations of uoro alcohol 1c
result in hydrogenation from the same face of the olen. The
predicted absolute conguration of hydrogenated product 2c is
S, which is in agreement as measured by the single crystal X-ray
structure of similar compound 2n.
The quadrant model also explains the lower enantiose-
lectivity of the E-isomer of aromatic allylic alcohol. For (E)-u-
oro alcohol 1c0, the two sterically favored orientations (Scheme
5h and i) feature coordination from opposite faces, which
results in the formation of a mixture of the R and S products.
The enantioselectivity predictions using the quadrant model
are in good agreement with the experimental results (Scheme 6)
as the (Z)-uoro alcohol 1c provided product 2c with high
enantioselectivity (97% ee) while the E isomer gave the corre-
sponding product 2c in only 65% ee.
Scheme 4 Synthesis of chiral fluorine molecule having different functional groups. Conditions: (i) CrO3, H2SO4, H2O, acetone, 1 h, 0 ꢀC; (ii)
(COCl)2, DMSO, TEA, 2 h, ꢁ78 to 0 ꢀC; (iii) ClSO2NCO, HCOOH, 0 ꢀC – r.t.
Chem. Sci.
This journal is © The Royal Society of Chemistry 2020

View Article Online
Edge Article
Chemical Science
Acknowledgements
The Swedish Research Council (VR), Stielsen Olle Engkvist
¨
Byggmastare, Knut and Alice Wallenberg Foundation (KAW
2018:0066) supported this work. We thank Dr Thishana Singh,
School of Chemistry and Physics, University of Kwazulu-Natal,
South Africa, for proofreading and editing the manuscript.
Notes and references
¨
1 (a) K. Muller, C. Faeh and F. Diederich, Science, 2007, 317,
1881–1886; (b) W. K. Hagmann, J. Med. Chem., 2008, 51,
4359–4369; (c) S. Purser, P. R. Moore, S. Swallow and
V. Gouverneur, Chem. Soc. Rev., 2008, 37, 320–330; (d)
S. M. Ametamey, M. Honer and P. A. Schubiger, Chem.
´
Rev., 2008, 108, 1501–1516; (e) J. Wang, M. Sanchez-
´
˜
Rosello, J. L. Acena, C. del Pozo, A. E. Sorochinsky,
S. Fustero, V. A. Soloshonok and H. Liu, Chem. Rev., 2014,
114, 2432–2506; (f) S. Dallongeville, N. Garnier, C. Rolando
and C. Tokarski, Chem. Rev., 2016, 116, 2–79.
˜
2 (a) Y. Zhou, J. Wang, Z. Gu, S. Wang, W. Zhu, J. L. Acena,
V. A. Soloshonok, K. Izawa and H. Liu, Chem. Rev., 2016,
116, 422–518; (b) E. P. Gillis, K. J. Eastman, M. D. Hill,
D. J. Donnelly and N. A. Meanwell, J. Med. Chem., 2015, 58,
8315–8359.
3 For reviews, see: (a) P. A. Champagne, J. Desroches,
J.-D. Hamel, M. Vandamme and J.-F. Paquin, Chem. Rev.,
2015, 115, 9073–9174; (b) G. Haufe, J. Fluorine Chem., 2004,
125, 875–894.
4 (a) R. M. Roe, V. Kallapur, R. J. Linderman and F. Viviani,
Pestic. Biochem. Physiol., 2005, 83, 140–154; (b)
Scheme 5 Determination of absolute configuration of olefin 1c using
catalyst F. (a–c) General fluorinated allylic alcohol in the selectivity
model of the ligand; (d–g) four different products obtained by different
possible coordination of Z isomer; (h and i) two different products
obtained by different possible coordination of E isomer.
¨
A. K. Podichetty, S. Wagner, S. Schroer, A. Faust,
¨
M. Schafers, O. Schober, K. Kopka and G. Haufe, J. Med.
Chem., 2009, 52, 3484–3495; (c) M.-Y. Chang, N.-C. Lee,
M.-F. Lee, Y.-P. Huang and C.-H. Lin, Tetrahedron Lett.,
2010, 51, 5900–5903; (d) A. J. Cresswell, S. G. Davies,
J. A. Lee, P. M. Roberts, A. J. Russell, J. E. Thomson and
M. J. Tyte, Org. Lett., 2010, 12, 2936–2939; (e)
A. J. Cresswell, S. G. Davies, J. A. Lee, M. J. Morris,
P. M. Roberts and J. E. Thomson, J. Org. Chem., 2011, 76,
4617–4627.
Scheme 6 Hydrogenation of both the Z and E isomer of vinyl fluoride
olefin 1c.
5 (a) E. L. Eliel, S. H. Wilen and L. N. Mander, in
Stereochemistry of Organic Compounds, John Wiley & Sons,
`
1994; (b) F. Cuevas, P. Ballester and M. A. Pericas, Org.
Conclusions
´
Lett., 2005, 7, 5485–5487; (c) S. Rodrıguez-Escrich, D. Popa,
`
C. Jimeno, A. Vidal-Ferran and M. A. Pericas, Org. Lett.,
In summary, we have developed a general and efficient catalyst
for the stereoselective synthesis of various uorohydrins, which
complements previous catalytic asymmetric syntheses of 1,2
uorohydrins. This method is straightforward and also
suppresses the problem of deuorination. The catalyst has been
used effectively on various aromatic and aliphatic trisubstituted
uorinated allylic alcohols, providing chiral 1,2 uorohydrins
in excellent yields and enantioselectivities.
´
2005, 7, 3829–3832; (d) M. Apparu, Y. B. Tiba, P.-M. Leo,
S. Hamman and C. Coulombeau, Tetrahedron: Asymmetry,
2000, 11, 2885–2898; (e) Y. Takeuchi, M. Konishi, H. Hori,
T. Takahashi, Y. Takeuchi, T. Kometani and K. L. Kirk,
Chem. Commun., 1998, 365–366; (f) S. Hamman,
M. Barrelle, F. Tetaz and C. G. Beguin, J. Fluorine Chem.,
1987, 37, 85–94.
6 F. Basolo and F. P. Dwyer, J. Am. Chem. Soc., 1954, 76, 1454–
1455.
7 (a) L. Mulki and C. S. Foster, Drugs Today, 2011, 47, 327–333;
(b) K. N. Jamal and D. G. Callanan, Clin. Ophthalmol., 2009, 3,
Conflicts of interest
There are no conicts to declare.
This journal is © The Royal Society of Chemistry 2020
Chem. Sci.

View Article Online
Chemical Science
Edge Article
381; (c) M. Korenfeld, Cataract and Refractive Surgery Today,
2008, 105–107; (d) A. Yancey, A. Armbruster and S. Tackett,
D. M. Sedgwick and G. B. Hammond, J. Fluorine Chem.,
2018, 207, 45–58.
J. Pharm. Technol., 2014, 31, 29–37; (e) V. Chagnault, 12 (a) M. Engman, J. S. Diesen, A. Paptchikhine and
M.-P. Jouannetaud, J.-C. Jacquesy and J. Marrot,
Tetrahedron, 2006, 62, 10248–10254.
P. G. Andersson, J. Am. Chem. Soc., 2007, 129, 4536–4537;
(b) P. Kaukoranta, M. Engman, C. Hedberg, J. Bergquist
and P. G. Andersson, Adv. Synth. Catal., 2008, 350, 1168–
1176; (c) A. Stumpf, M. Reynolds, D. Sutherlin, S. Babu,
E. Bappert, F. Spindler, M. Welch and J. Gaudino, Adv.
Synth. Catal., 2011, 353, 3367–3372; (d) S. Ponra,
W. Rabten, J. Yang, H. Wu, S. Kerdphon and
P. G. Andersson, J. Am. Chem. Soc., 2018, 140, 13878–
13883; (e) Z. Han, Y.-Q. Guan, G. Liu, R. Wang, X. Yin,
Q. Zhao, H. Cong, X.-Q. Dong and X. Zhang, Org. Lett.,
2018, 20, 6349–6353; (f) Y.-Q. Guan, Z. Han, X. Li, C. You,
X. Tan, H. Lv and X. Zhang, Chem. Sci., 2019, 10, 252–256;
(g) S. Kerdphon, S. Ponra, J. Yang, H. Wu, L. Eriksson and
P. G. Andersson, ACS Catal., 2019, 9, 6169–6176.
8 (a) Q. Zhang and H. M. Nguyen, Chem. Sci., 2014, 5, 291–296;
(b) G. Haufe and S. Bruns, Adv. Synth. Catal., 2002, 344, 165–
171; (c) G. Haufe, S. Bruns and M. Runge, J. Fluorine Chem.,
2001, 112, 55–61; (d) M. Shimizu and Y. Nakahara, J. Fluorine
Chem., 1999, 99, 95–97; (e) R. Skupin and G. Haufe, J. Fluorine
Chem., 1998, 92, 157–165; for a study on the regioselectivity
of the ring opening with different sources of nucleophilic
uoride, see: (f) A. Sattler and G. Haufe, J. Fluorine Chem.,
1994, 69, 185–190; for seminal contributions, see: (g)
G. A. Olah, J. T. Welch, Y. D. Vankar, M. Nojima, I. Kerekes
and J. A. Olah, J. Org. Chem., 1979, 44, 3872–3881; (h)
G. A. Olah and D. Meidar, Isr. J. Chem., 1978, 17, 148–149.
`
´
9 (a) O. Pamies, P. G. Andersson and M. Dieguez, Chem.–Eur. 13 S. Kang and H.-K. Lee, J. Org. Chem., 2010, 75, 237–240.
J., 2010, 16, 14232–14240; (b) A. Lightfoot, P. Schnider and 14 (a) T. L. Church, T. Rasmussen and P. G. Andersson,
A. Pfaltz, Angew. Chem., Int. Ed., 1998, 37, 2897–2899; (c)
X. Cui and K. Burgess, Chem. Rev., 2005, 105, 3272–3296.
10 S. Ponra, J. Yang, S. Kerdphon and P. G. Andersson, Angew.
Chem., Int. Ed., 2019, 58, 9282–9287.
Organometallics, 2010, 29, 6769–6781; (b) P. Brandt,
C. Hedberg and P. G. Andersson, Chem.–Eur. J., 2003, 9,
339–347; (c) Y. Fan, X. Cui, K. Burgess and M. B. Hall, J.
Am. Chem. Soc., 2004, 126, 16688–16689.
11 (a) M. Hudlicky, Chemistry of Organic Fluorine Compounds, 15 C. Mazet, S. P. Smidt, M. Meuwly and A. Pfaltz, J. Am. Chem.
2nd edn, Ellis Harwood, Chichester, 1992; (b) Soc., 2004, 126, 14176–14181.
Chem. Sci.
This journal is © The Royal Society of Chemistry 2020