Size-Exclusion Borane-Catalyzed Domino 1,3-Allylic/Reductive Ireland–Claisen Rearrangements: Impact of the Electronic and Structural Parameters on the 1,3-Allylic Shift Aptitude

Article abstract of DOI:10.1002/chem.201805208

The reductive Ireland–Claisen rearrangement through borane-mediated hydrosilylation is reported. The method employs a borane catalyst with a special structural design and affords access to synthetically relevant products with high diastereoselectivity. Depending on electronic and structural parameters, the reaction can be coupled with a 1,3-allylic shift, thus the valence isomer of the Ireland–Claisen product is formed.

Full text of DOI:10.1002/chem.201805208

A Journal of
Accepted Article
Title: Size-Exclusion Borane Catalyzed Domino 1,3-Allylic/Reductive
Ireland-Claisen Rearrangements. Impact of the Electronic and
Structural Parameters on the 1,3-Allylic Shift Aptitude
Authors: Tibor Soos, Dániel Fegyverneki, Natália Kolozsvári, Dániel
Molnár, Orsolya Egyed, and Tamás Holczbauer
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201805208
Link to VoR: http://dx.doi.org/10.1002/chem.201805208
Supported by

10.1002/chem.201805208
Chemistry - A European Journal
COMMUNICATION
Size-Exclusion Borane Catalyzed Domino 1,3-Allylic/Reductive
Ireland-Claisen Rearrangements. Impact of the Electronic and
Structural Parameters on the 1,3-Allylic Shift Aptitude
Dániel Fegyverneki, Natália Kolozsvári, Dániel Molnár, Orsolya Egyed, Tamás Holczbauer and Tibor
Soós*
Abstract: The reductive Ireland-Claisen rearrangement via borane
mediated hydrosilylation is reported. The method employs borane
catalyst with a special structural design and affords access to
synthetically relevant product with high diastereoselectivity.
Depending on electronic and structural parameter, the reaction can
be coupled with a 1,3-allylic shift, thus the valence isomer of the
Ireland-Claisen product is formed.
In a dual attempt to further the reductive Ireland-Claisen
rearrangement in scope and practicality, we aimed to develop its
borane-catalyzed version to amplify substrate scope and
significantly upgrade user-friendliness. We assumed that the
borane catalyst would promote both the 1,4-hydrosilylation of
allyl acrylates and also the rearrangement of the formed silyl
ester enolate to afford the appropriate Ireland-Claisen product in
a one-pot manner. Additionally, it was expected that utilization of
boron-based catalyst would be advantageous as these metal-
Since its discovery in 1912, the Claisen rearrangement has
evolved into a powerful synthetic tool for stereoselective carbon–
carbon bond formation.[1] Much of its current popularity is due to
the subsequent development of a series of new variants to effect
free catalysts exhibit different chemoselectivity and functional
[10]
group tolerance
than transition metal catalysts in reductive
processes. However, the adaptation of borane promoted
hydrosilylation for reductive Ireland-Claisen rearrangement was
far from being straightforward because of the substrate inhibition
and the extreme water sensitivity of the highly oxophilic, hard-
type boron catalyst. Nevertheless, based on our previous work
in frustrated Lewis pair hydrogenation [11] and hydrosilylation,[12]
we conceived that it is possible to tackle these anticipated
constrains of a borane catalyzed reductive Ireland-Claisen
rearrangement via employing structurally well-designed, so-
called size-exclusion boranes. The enhanced steric shielding
around the boron Lewis acid center would serves to prevent or
retard the complexation ability with Lewis basis (including water
and carbonyls’ oxygen), while retaining the capacity of cleavage
of the silanes and might drive the chemo- and regioselectivity of
this [3,3]-sigmatropic rearrangement in
a stereocontrolled
manner. Among these variants, the Ireland-Claisen reaction has
proven to be the most general method, as this rearrangement
requires significantly lower reaction temperature and there exists
a unique option to control the silyl ester enolate geometry
through the judicious choice of solvent (Scheme 1).[2]
Nevertheless, one often-cited drawback of the classical Ireland-
Claisen rearrangement is its inherent reliance on the usage of
strong bases to provide the requisite silyl ester enolates. As a
result, the substrate scope of this rearrangement is bounded as
certain functionalities are not tolerated and the silyl ester enolate
forming process requires rather low temperature. Consequently,
the alternative construction of the requisite silyl ester enolates[3-7]
is a particularly promising direction in Ireland-Claisen chemistry.
Thanks to the availability of effective catalysts for reductive
silyl ester enolate formation, one-pot 1,4-hydrosilylation of allyl
acrylates/[3,3] sigmatropic rearrangement protocols have been
developed. First, Morken disclosed a highly diastereoselective
rhodium catalyzed reductive Ireland-Claisen rearrangement
using Cl2MeSiH as a stoichiometric reducing agent.[8] Recently,
Chiu has advanced further this reductive approach using in situ
generated copper hydride catalyst and a less water-sensitive
diethoxymethyl-silane reducing agent. Despite the many
advances, the reductive Ireland-Claisen rearrangements still lag
behind in scope and practicality. As such, the employed metal
catalysts have had limited functional group tolerance and the
reported protocols have a reliance and dependence on the glove
box because of need of rigorous exclusion of water.[9] (Scheme
1.)
the hydrosilylation of acrylates.
Previous work:
O
anti
O
1
3
TBSO
.
L
D
H
2
2
.
T
A
,
%
F
O
HO
H
l
M
T
Ireland
B
,
P
S
A
A
/
T
O
C
D
L
C
l
OTBS
.
H
O
S
1
B
F
T
.
O
O
2
Z,Z
E,E
O
F
1
TBSO
E
.
Z
L
H
D
H
2
T
A
3
,
,
%
O
A
B
l
2
D
L
.
HO
.
C
T
M
S
B
1
.
P
S
O
A
T
C
/
OTBS
2
T
l
H
F
E,Z
syn
Numbering:
Z,E
O
OSi
O
OSiR3
[(cod)RhCl]2
MeDuPhos
Cl2MeSiH
2
O
OH
OH
O
O
3
1
O
Morken
6
n-Pr
n-Pr
4
n-Pr
n-Pr
n-Pr
5
O
OSi
O
LCuH
(EtO)2MeSiH
O
Chiu
This work:
R
OSiR3
n-Pr
Cl
2
1
O
3
5
4
O
O
O
catalyst(I):
Cl
F
Cl
catalyst(I)
Et3SiH
F
O
HO
OH
Ar
B
or
F
F
Ar
R
F
Ar
F
F
F
Scheme 1. Prior art and numbering of Ireland-Claisen rearrangements via silyl
D. Fegyverneki, N. Kolozsvári, D. Molnár, Dr. O. Egyed, Dr. T.
Holczbauer, Dr. T. Soós
ester enolates.
Institute of Organic Chemistry, Research Centre of Natural
Sciences, Hungarian Academy of Sciences, 2 Magyar tudósok krt.,
Budapest, Hungary, 1117
On the basis of the precedent in size-exclusion FLP
hydrogenation and hydrosilylation reactions, we attempted a
borane mediated reductive Ireland-Claisen rearrangement using
bulky borane I. Gratifyingly, the model substrate 4-phenylallylic
acrylate (1a) underwent the proposed catalytic transformation
with stoichiometric Et3SiH. Further evaluation of a variety of
E-mail: soos.tibor@ttk.mta.hu
Supporting information for this article is given via a link at the end of
the document.
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10.1002/chem.201805208
Chemistry - A European Journal
COMMUNICATION
borane catalysts and experimental conditions (concentration,
catalyst load) led to the identification of optimal reaction
condition for the two-step tandem process. A subsequent survey
of reaction solvent found toluene to be superior to ethereal type
solvents, and most importantly, even technical grade solvent
could be used. As catalyst I proved to be air and moisture
stable, we performed all synthetic manipulation, as well as all
others reported in this study, at laboratory bench without the
reliance and dependence on inert techniques. Although the
presence of water did not mitigate the reaction, our preliminary
results also indicated that a small excess of silane was needed
to reach full conversion in the hydrosilylation step.[13]
Next, we conducted an experiment to probe the
diastereoselectivity of the cascade reaction. However, when a
methyl substituent was introduced into position 6, the product
was not the expected Ireland-Claisen product (Scheme 2).
Further structural information derived from NMR spectroscopy
and X-ray crystallography indicated the formation of a formal
valence isomer with syn diastereoselectivity. As it is known that
allylic esters can rearrange in the presence of Lewis and
Brønsted acids[14], we assumed that a 1,3-allylic shift preceded
the sigmatropic rearrangement.[15] Nevertheless, the syn
diastereoselectivity of the rearrangement revealed that the
factor in this reductive Ireland-Claisen reaction. The sterically
less demanding B(C6F5)3 II,[19] which is the archetypical borane
of frustrated Lewis pair chemistry, failed to deliver any products
under the same reaction condition and gave only
multicomponent mixture.[13]
a
As seemingly slight structural modification would change
the 1,3 allylic shift aptitude (1a vs 1b), we became interested to
determine how electronic and structural parameters affect the
1,3-allylic transposition (Table 1). As hidden Brønsted catalyst
proved to be an efficient promoter in this rearrangement, we
deliberately generated the Brønsted acid catalyst using borane I
in technical grade, “wet” toluene solvent. Examining the impact
of the electronic effects on reactivity of 1a acetyl analogs
showed that the electron-donating substituents in para position
on the aromatic ring lowered the activation barrier and full
conversion to the thermodynamically more stable styrene
derivatives was observed within one hour at room temperature
(Table 1, entries 1–3). However, similar to what we have
observed before, there was no allylic rearrangement without
activating group at room temperature, but the process did take
place at elevated the temperature and elongated reaction time
(Table 1, entry 4). Introducing electron-withdrawing substituents
resulted also decreased reactivity, there was no reaction in case
of trifluoromethyl substituent even under forcing reaction
condition (Table 1, entries 5, 6). Introducing substituents into
position 5 facilitated the rearrangement, smooth transformation
occurred at room temperature. (Table 1, entries 7–10). However,
acetates of primary allylic alcohols did not rearrange even at
elevated temperature showing that an electron rich aromatic
substituent at position 4 is a requisite for this transformation
(Table 1, entries 11,12). To determine whether the allylic
rearrangement was the result of an inter- or an intramolecular
process, a crossover experiment was performed.[13] As no
crossover products formation was detected, the allylic
rearrangement seems to follow an intramolecular mechanism.
hydrosilylation step prefers
a Z-selective silyl enol ether
formation which selectivity is in agreement with our previous
observation in related borane mediated 1,4-hydrosilylation of
unsaturated ketones.[12]
O
O
OSiEt3
1.5 eq. HSiEt3
2 mol% Ar3B(I)
O
HO
O
via
toluene, RT
Ph
1a
O
2a 92%
O
O
1.5 eq. HSiEt3
2 mol% Ar3B(I)
OH
toluene, RT
1b
5b 71%
Table 1. Hidden Brønsted acid mediated 1,3-allylic rearrangement of allylic
acetates using borane I in “wet” toluene.
O
hindered
proton catalysis
H
Et3Si
O
O
HSiEt3
Ar3B (I)
Ar3B (I)
O
H
O
"wet" toluene
1,3-allylic migration
[3,3]-sigmatropic
rearrangement
hydrosilylation
Cl
catalyst
Cl
O
O
Cl
O
2 mol% I
O
F
F
B
"wet" toluene, RT, 2h
R'
F
F
R'
F
F
SiR3
F
F
R
R3Si
R
3a-m
4a-m
I
Lewis acid induced
Lewis acid catalysis
Ar3B-H
O
O
Ar3B-H
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
HSiEt3
Ar3B (I)
1
2
3a
4a
4b
99(72)
99(74)
99(97)
7
8
3g
4g
99(21)
99(80)
O
O
O
O
O
O
O
Ph
Me
Ph
Ph
Me
anhydrous
toluene
Si-H activation
O
MeO
Me
Et
MeO
O
1,3-allylic
migration
O
O
O
O
3b
3h
Et
4h
Et
Ar3B(I) = B(C6F4H)2(C6Cl3H2
)
Ph
O
O
Me
Et
O
O
3
4
3c
3d
4c
4d
9
3i
4i
99(83)
99(96)
O
O
O
O
Scheme 2. Hydrosilylation/ Ireland-Claisen tandem reactions and proposed
reaction pathways forming classical and formal valence isomer products.
Ph
Ph
Pr
Ph
Ph
Pr
99(73)b
99(65)b
10
3j
4j
Bu
Bu
O
O
O
O
O
O
R=Pr 0(-)
R=Bu 0(-)
5
6
3e
3f
4e
4f
11
12
3k,l
4k,l
O
O
O
Subsequent studies revealed that the borane I itself was
incapable to promote the 1,3-allylic shift because of the confined
space around the Lewis acidic center. However, as our
observations[13] suggest, the allylic transposition (Scheme 2)
could proceed via either a Lewis acid induced Lewis acid
promotion (hydride abstraction from HSiEt3 with borane I)[16] or
hidden proton catalysis[17] (protonation by trace amount of
borane I-water adduct[11,18]). Finally, it was established that the
enhanced steric hindrance around the borane I was a critical
R
R
Cl
Cl
O
O
O
O
0(-)
3m
Ph
4m
Ph
0(-)
O
F3C
F3C
(a)Reaction conditions: in a capped vial, acetate (1.0 mmol), borane I (0.02
mmol) in 8 mL of “wet“ toluene was stirred at RT for 2h. Conversions were
determined by 1H-NMR (b) reaction was conducted at 60°C for 16h.
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10.1002/chem.201805208
Chemistry - A European Journal
COMMUNICATION
Given the effects of substituents on the 1,3-allylic migration,
we aimed to interweave this reactivity with the
hydrosilylation/Ireland-Claisen rearrangement reaction cascade
by the judicious choice of substituent on the aromatic ring (Table
2). Compounds with electron-withdrawing substituents did not
give the preceding 1,3-rearrangement and resulted in the
classical 2-step cascade products respectively (Table 2, entries
1–8). These experiments also indicated that the reactions were
not affected by the position of the substituent (Table 2, entries
5–7). As expected, the presence of electron-donating
substituents on the phenyl ring facilitated the allylic
rearrangement, resulting in the formation of formal valence
isomer products via 3-step reaction cascade. In case of alkyl
group at para position, the desired 3-step cascade compounds
were obtained with high diastereoselectivity (Table 2, entries
9,10). As the geometry of the allylic double bond in the starting
material was trans, the diastereomeric ratio of the [3,3]-
sigmatropic rearrangement step was determined by the
geometrical selectivity of the hydrosilylation step on the newly
formed enolate double bond.
Next, the effect of substitution at position 6 was examined (for
numbering see Scheme 1). As expected, allylic acetates with
alkyl chain were readily converted in the 1,3-allylic
rearrangement/hydrosilylation/Ireland-Claisen
rearrangement
cascade to unsaturated carboxylic acid products with syn
diastereoselectivity (Table 3, entries 2–6). Expanding the scope
of the unsaturated acid part also allowed transforming crotylate
esters with the method albeit yields were lower (Table 3, entry 7).
To perform our reaction cascade in the presence of heteroaryl
rings seemed to be challenging due to their possible
coordination to Lewis acid catalyst I. To our delight, the reaction
went smoothly in the presence of thiophene ring (Table 3, entry
8). Substituents at position 6 (for numbering see Scheme 1)
afforded the diastereoselective formation of the 2,3-disubstituted
products without allylic rearrangement, therefore allowed to
obtain products that are not accessible from substrate with
substitution at position 4 (Table 3, entries 9,10).
Table 3. Domino 1,3-allylic/reductive Ireland-Claisen rearrangements of 6-
substituted allylic acrylates.
Table 2. Domino 1,3-Allylic/reductive Ireland-Claisen rearrangements of 4-aryl
allylic acrylates.
O
O
O
1. 2 mol% catalyst (I)
2. 1.5 eq. HSiEt3
Cl
Cl
HO
Ph
Cl
F
OH
O
or
16 h
F
F
B
R1
R
Ph
R
"wet" toluene, 0- 25°C
F
F
F
F
2-step cascade
2a-w
3-step cascade
5a-w
F
I
1a-w
O
O
O
1. 2 mol% catalyst (I)
2. 1.5 eq. HSiEt3
HO
Ar
OH
O
O
O
O
O
3-step cascade
2-step cascade
2c-p
or
16 h
64%,
d.r. 20:1
1c-p
Ar
R
5c-p
O
Ar
"wet" toluene, 0- 25°C
92%
O
OH
1
2
1a
2a
5b
6
1t
5t
O
O
HO
Ph
O
O
O
O
Ph
C7H15
Ph
Et
C7H15
Ph
Ph
O
O
HO
2c
O
HO
2j
O
O
O
O
1j
1c
1d
1e
1
2
3
62%
71%
63%
8
9
81%
71%,
d.r. >30:1
43%,
d.r. 9:1
O
1b
7
1u
5u
OH
CH3
OH
O
O
O
O
O
O
O
O
O
O2N
O2N
F
Me
Et
F
Ph
C2H5
O
HO
O
O
O
O
OH
OH
OH
CH3
Ph
Ph
C2H5
2d
2e
1k
1l
5k
5l
65% d.r. 9:1
60%, d.r. 15:1
O
O
O
O
O
OH
Me
O
64%,
d.r. 17:1
43%,
d.r. 6:1
O
OH
C2H5
F3C
F3C
3
4
5
1q
5q
5r
8
9
1v
5v
Me
Et
O
HO
O
S
S
10
Ph
Ph
Ph
C2H5
Ph
O
O
O
O
O
O
O
O
Br
Br
71%
d.r. 12:1
76%,
d.r. 7:1
O
Br HO
O
O
OH
C3H7
1r
C3H7
1w
2w
2x
O
HO
1m
1n
5m
2n
4
5
1f
88%
74%
11
12
66%, d.r. 5:1
81%
2f
Ph
Ph
C4H9
C4H9
O
O
MeO
MeO
MeO
MeO
Br
O
O
HO
HO
1g
2g
71%,
d.r. 13:1
63%,
d.r. 12:1
OH
C4H9
1s
C4H9
5s
10
1x
O
HO
O
O
O
O
O
O
O
O
Ph
Ph
Cl
Cl
O
HO
2h
OMe O
OMe
OH
1o
1h
1i
6
7
88%
86%
13
14
5o
46% d.r. 6:1
81%(1:1)
Cl
Cl
HO
2p+2q
O
HO
2i
O
1p
Reaction conditions: in a septum-capped vial, acrylate (1.0 mmol), I (0.02
mmol) in 8 mL of “wet“ toluene were stirred for 1 hour at RT, then Et3SiH (1.5
mmol) was added at 0°C. (a) Diastereomeric ratio was determinded by 1H-NMR.
(OHC)MeOOC
Cl
Cl
MeOOC
Reaction conditions: in a septum-capped vial, acrylate (1.0 mmol), I (0.02
mmol) in 8 mL of “wet“ toluene were stirred for 1 hour at RT, then Et3SiH (1.5
mmol) was added at 0°C. (a) Diastereomeric ratio was determinded by 1H-NMR.
(b) 1:1 mixture of products.
In summary, a metal-free, one-pot reductive Ireland-Claisen
rearrangement has been developed. With the applied air and
moisture tolerant borane Lewis acid I a two or three-step tandem
reaction cascade can be processed to form the Claisen products
with good yields and high diastereoselectivity. As the syn
diastereomer product proved to be the major product of the
reaction, the 1,4-hydrosilylation step should form the Z-enolate
respectively, which preference is the opposite of the metal
catalyzed alternatives. The utilization of designer boron Lewis
acid I represent not only a metal-free alternative but alleviated
various restrictions of previous rearrangements, thus, the
synthetic manipulations can be performed at the laboratory
bench without the reliance and dependence on glove box and
there was no need for purification of the solvent and reagents.
Since the method requires mild reaction conditions, it
establishes a practical alternative over the traditional Ireland-
Claisen methods.
The effect of the methoxy group was also systematically
investigated (Table 2, entries 11–13). The substituent exerted
its electron-donating effect in ortho and para positions, resulting
in the formation of the 2,3-disubstituted unsaturated 5m,o
carboxylic acid derivatives. However, at meta position, methoxy
group showed electron-withdrawing effect that could be foreseen
from the σ Hammett-constants and afforded 2n in a two-step
hydrosilylation/Ireland-Claisen rearrangement cascade process.
Introducing an ester group resulted in more complex
transformation. As 0.5 equivalent excess of silane reagent was
used, 50% of the 2p product was reduced to 2q 4-formyl
compound (Table 2, entry 14).
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10.1002/chem.201805208
Chemistry - A European Journal
COMMUNICATION
[5]
[6]
M. Eriksson, A. Hjelmencrantz, M. Nilsson, T. Olsson, Tetrahedron
1995, 51, 12631–12644.
Experimental Section
K. Takai, T. Ueda, H. Kaihara, Y. Sunami, T. Moriwake, J. Org. Chem.
1996, 61, 8728–8729.
General procedure of tandem reactions
[7]
[8]
[9]
Y. Li, Q. Wang, A. Goeke, G. Fráter, Synlett 2007, 288–292.
S. P. Miller, J. P. Morken, Org. Lett. 2002, 4, 2743–2745.
K. C. Wong, E. Ng, W-T. Wong, P. Chiu, Chem. Eur. J. 2015, 22,
3709–3712.
In a 20 mL septum-capped vial equipped with a magnetic stirring bar,
starting ester (1.0 mmol) and I (10 mg, 0.02 mmol, 2.0 mol%) was
dissolved in 8 mL of technical grade, “wet” toluene. The reaction was
stirred for 1 hour (this step is not required for the 2-step cascade). Then
the mixture was cooled to 0°C with an ice/water bath. Et3SiH (176 mg,
1.5 mmol, 1.5 equiv.) was added dropwise via syringe. The reaction was
left to warm to room temperature and stirred overnight. After completion,
TBAF (2 equiv.) was added and the reaction was stirred for 15 minutes.
Then 8 mL 10% HCl solution was added and the mixture was stirred for
15 minutes. The phases were separated and the water phase was
extracted with 2x5 mL of toluene. The organic phases were collected and
dried on Na2SO4. Solvent was evaporated, and crude product was
purified with flash chromatography (eluent: hexanes/EtOAc/acetic acid:
100/10/1) to obtain the desired carboxylic acid.
[10] For recent review on borane-catalyzed hydrosilylations, see: M.
Oestreich, J. Hermeke, J. Mohr, Chem. Soc. Rev. 2015, 44, 2202–2220.
[11] a) Á. Gyömöre, M. Bakos, T. Földes, I. Pápai, A. Domján, T. Soós, ACS
Catal. 2015, 5, 5366–5372; b) M. Bakos, Á. Gyömöre, A. Domján, T.
Soós, Angew. Chem. 2017, 129, 5301–5305; Angew. Chem. Int. Ed.
2017, 56, 5217–5221; c) É. Dorkó, M. Szabó, B. Kótai, I. Pápai, A.
Domján, T. Soós Angew. Chem. 2017, 129, 9640-9644; Angew. Chem.
Int. Ed. 2017, 56, 9512–9516.
[12] D. Fegyverneki, Á. Gyömöre, O. Egyed, T. Soós, Org. Lett. manuscript
submitted.
[13] See Supporting Information for details.
[14] For some selected examples, see: a) N. Marion, R. Gealageas, S. P.
Nolan, Org. Lett. 2007, 14, 2653–2656; b) L. M. Stanley, C. Bai, M.
Ueda, J. F. Hartwig, J. Am. Chem. Soc. 2010, 26, 8918–8920; c) A.
Serra-Muns, A. Guérenot, S. Raymond, J. Cossy, Chem. Comm. 2010,
46, 4178–4180.
Acknowledgements
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This work was supported by the National Research,
Development and Innovation Office (K-116150). We are grateful
for the technical support from Servier Research Institute of
Medicinal Chemistry.
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Keywords: sigmatropic rearrangement • boranes • silanes •
Ireland-Claisen • diastereoselectivity
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[4]
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10.1002/chem.201805208
Chemistry - A European Journal
COMMUNICATION
Entry for the Table of Contents (Please choose one layout)
Layout 2:
COMMUNICATION
Dániel Fegyverneki, Natália Kolozsvári,
Dániel Molnár, Orsolya Egyed, Tamás
Holczbauer and Tibor Soós*
O
O
OSiEt3
[3,3]
HO
O
O
MeO
H+ MeO
MeO
Cl
Cl
- ambient temperature
- no glove box
technical grade solvent
Cl
1.
F
2 mol%
F
B
2- or 3-step reductive Ireland-Claisen cascade
24 examples, 43-91%, dr up to 20:1
F
F
-
F
F
F
O
F
Page No. – Page No.
O
O
OSiEt3
2. Et3SiH
OH
O
O
[3,3]
O
H+
MeO
MeO
Size-Exclusion Borane Catalyzed
Domino 1,3-Allylic/Reductive Ireland-
Claisen Rearrangements. Impact of
the Electronic and Structural
Parameters on the 1,3-Allylic Shift
Aptitude
MeO
syn
The reductive Ireland-Claisen rearrangement via borane mediated hydrosilylation is
reported. The method employs borane catalyst with a special sterical design and
affords access to synthetically relevant product with high diastereoselectivity.
Depending on electronic and structural parameter, the reaction can be coupled with
a 1,3-allyl shift, thus the valence isomer of the Ireland-Claisen product is formed.
This article is protected by copyright. All rights reserved.