Morita–Baylis–Hillman-Type [3,3]-Rearrangement: Switching from Z- to E-Selective α-Arylation by New Rearrangement Partners

Article abstract of DOI:10.1002/anie.202100497

α-aryl α,β-unsaturated carbonyls represent an important class of derivatizable synthetic intermediates, however, the synthesis of such compounds still remains a challenge. Recently, we showcased a novel Z-selective α-arylation of α,β-unsaturated nitriles with aryl sulfoxides via [3,3]-rearrangement involving an Morita–Baylis–Hillman (MBH) process. Herein, we demonstrate the feasibility of reversing the stereoselectivity of such MBH-type [3,3]-rearrangement by switching to a new pair of rearrangement partners consisting of aryl iodanes and α,β-unsaturated oxazolines. As a result, the two protocols complement each other in approaching E- or Z-α-aryl α,β-unsaturated carbonyl derivatives. Mechanistic studies reveal a possible reaction pathway and provide an explanation for the opposite stereoselectivities.

Full text of DOI:10.1002/anie.202100497

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How to cite: Angew. Chem. Int. Ed. 2021, 60, 11414–11422
International Edition:
German Edition:
doi.org/10.1002/anie.202100497
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Synthetic Methods
Morita–Baylis–Hillman-Type [3,3]-Rearrangement: Switching from
Z- to E-Selective a-Arylation by New Rearrangement Partners
Lei Zhang+, Wangzhen Bao+, Yuchen Liang+, Wenjing Pan, Dongyang Li, Lichun Kong, Zhi-
Xiang Wang,* and Bo Peng*
Abstract: a-aryl a,b-unsaturated carbonyls represent an
important class of derivatizable synthetic intermediates, how-
ever, the synthesis of such compounds still remains a challenge.
Recently, we showcased a novel Z-selective a-arylation of a,b-
unsaturated nitriles with aryl sulfoxides via [3,3]-rearrange-
ment involving an Morita–Baylis–Hillman (MBH) process.
Herein, we demonstrate the feasibility of reversing the stereo-
selectivity of such MBH-type [3,3]-rearrangement by switching
to a new pair of rearrangement partners consisting of aryl
iodanes and a,b-unsaturated oxazolines. As a result, the two
protocols complement each other in approaching E- or Z-a-
aryl a,b-unsaturated carbonyl derivatives. Mechanistic studies
reveal a possible reaction pathway and provide an explanation
for the opposite stereoselectivities.
synthetic community.[5,6] This type of rearrangement can be
conducted by directly mixing readily available activated aryl
iodanes and aryl sulfoxides with certain nucleophiles,[7–11]
which allows in situ construction of a highly reactive transient
rearrangement precursor. In this context, we were interested
in constructing the rearrangement precursor in a stepwise
fashion which, we conceived, not only enhances the reaction
efficiency but also render the reaction capable of adopting
new intriguing functions.[12,13] For examples, with the stepwise
strategy, we were able to implement [3,3]- and [5,5]-rear-
rangement of aryl sulfoxides with alkyl nitriles and allyl
nitriles, respectively, via an assembly/deprotonation
sequence.[12] The same protocol also allows us to develop
asymmetric [3,3]-rearrangement of aryl iodanes with chiral
oxazolines.[13]
Introduction
Recently, the stepwise strategy continued to illuminate us
to merge Morita–Baylis–Hillman (MBH) reaction with the
rearrangement chemistry.[14,15] As depicted in Scheme 1, the
addition/elimination of MBH process could be merged with
the rearrangement of aryl sulfoxides and aryl iodanes. As
a result, the MBH-type rearrangement of aryl sulfoxides
a-Aryl a,b-unsaturated carbonyls are valuable synthetic
building blocks.[1] Traditional methods to synthesize these
molecules rely on the cross coupling of a-halogenated or
metalated a,b-unsaturated carbonyls with a proper arene
moiety source.[2] However, the use of prefunctionalized a,b-
unsaturated carbonyls decreases the step efficiency of such
À
enables Z-selective a-C H arylation of a,b-unsaturated
nitriles as we disclosed recently (Scheme 1B).[15] In contrast
with the established Z-selectivity, we herein describe an
E-selective MBH-type rearrangement by employing a new
pair of rearrangement partners consisting of aryl iodanes and
a,b-unsaturated oxazolines (Scheme 1C). Henceforth, with
these two MBH-type rearrangements in hand, both E- and Z-
a-aryl a,b-unsaturated carbonyl derivatives can now be
accessed on demand by switching to a proper rearrangement
partners. In this Article, we also describe mechanistic studies
towards understanding the intriguing opposite stereoselectiv-
ities associated with such two MBH-type rearrangement
reactions.
À
protocols. Direct a-C H arylation of a,b-unsaturated carbon-
yls is a straightforward approach, but it has rarely been
developed.[3] In 2004, Krische and co-workers accomplished
a-arylation of enones and enals with triarylbismuth reagents
via nucleophilic catalysis.[3a] Despite the impressive step
efficiency, the difficulty in synthesizing unconventional bis-
muth reagents limits the adoption of the protocol.[4] There-
À
fore, the development of efficient stereoselective a-C H
arylation of a,b-unsaturated carbonyls is highly desirable.
In the past few years, the iodonium- and sulfonium-
Claisen rearrangements have attracted great attention from
Notably, while our study was underway, Wengryniuk
reported an elegant iodine(III)-Claisen rearrangement of
b-pyridinium silyl enol ethers that allows for a-arylation of
a,b-unsaturated ketones (Scheme 2).[16] Unlike our method,
the reagents and substrates of Wengryniukꢀs protocol were
employed in a different order. As a result, the reported
reaction is mechanistically different with our protocol. In
their reaction, TMSOTf and base were added to enones for
forming silyl enol ethers which then undergo a metathesis
with aryl iodanes to construct enolate-iodonium rearrange-
ment precursors. However, the generation of such unconven-
tional silyl enol ethers, called b-pyridinium silyl enol ethers,
suffers from limited substrate scope[17] that generally restricts
the reaction scope to structurally defined cyclic enones.
[*] L. Zhang,[+] W. Bao,[+] W. Pan, D. Li, L. Kong, Prof. B. Peng
Key Laboratory of the Ministry of Education for Advanced Catalysis
Materials, Zhejiang Normal University
Jinhua 321004 (China)
E-mail: pengbo@zjnu.cn
Y. Liang,[+] Prof. Z.-X. Wang
School of Chemical Sciences
University of the Chinese Academy of Sciences
Beijing 100049 (China)
E-mail: zxwang@ucas.ac.cn
[+] These authors contributed equally to this work.
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
https://doi.org/10.1002/anie.202100497.
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including a,b-unsaturated nitrile 2a, aldehyde 2b, ketone 2c,
ester 2d, amide 2e, imidate 2 f, imine 2g, oxime 2h and
2-oxazoline 3a, as shown by entries 1–9 in Table 1. DABCO,
which is often used as Lewis base for the MBH reaction, was
employed for our initial exploration. Although no desired
products 4a–4h could be determined from the reactions of
2a–2h, a,b-unsaturated oxazoline 3a was found to be
promising for the transformation albeit giving desired product
5aa in low yield (19%) (entry 9). The feasibility of oxazoline
3a could be attributed to its higher nucleophilicity than other
unsaturated carbonyls, which enhanced its interaction with
aryl iodanes. Probably, due to the same factor, we could
successfully achieve asymmetric rearrangement of aryl
iodanes with chiral oxazolines.[13] Further studies revealed
that the choice of bases was also critical to the reaction.
Pyridine derivatives were more effective than aliphatic
tertiary amines (entries 10–13). Further optimization of the
reaction temperatures and reaction times identified the best
conditions giving 5aa in 71% yield (entry 16).[18]
With the optimized conditions in hand, we investigated
the reaction scope with respect to a,b-unsaturated oxazolines
3 and aryl iodanes (Scheme 3). Impressively, the reaction
demonstrated excellent E-selectivity when facing with a wide
variety of a,b-unsaturated oxazolines 3. Regardless of the
length of the terminal alkyl chains, oxazolines 3b–3d
smoothly afforded 5ab–5ad in similar yields (69–72%). The
method was also applicable to bulky oxazolines 3g–3k
bearing b-cyclopropyl, cyclopentyl, cyclohexyl, cyclohexenyl,
and piperidine groups that afforded stereohindered alkenes
5ag–5ak in synthetically useful yields (47–57%). Remark-
ably, b,b’-dimethyl substituted oxazoline 3l could even furnish
tetrasubstituted alkene 5al, albeit in a low yield (25%). In
addition to b-alkyl oxazolines, b-aryl oxazoline 3m and 3n
also proved suitable for the process giving 5am and 5an in
modest yields. Further studies demonstrated that the reaction
possessed excellent functional group (FG) compatibility. An
array of FGs including alkene groups (5aj, 5ay and 5aa’),
protected amines (5ak and 5ab’), alkyl/aryl halides (5ao, 5au,
5av and 5az), ethers (5ap–5ar, 5aw and 5ax), esters (5as–5av
and 5ay–5aa’), propargyl groups (5aw), and nitrile groups
(5ax) were all well tolerated in the reaction. Notably, alkene,
alkynyl and heteroaryl groups that could be readily oxidized
by hypervalent iodines were also tolerated here. This uncon-
ventional FG compatibility could be attributed to the
relatively high affinity of oxazolines with iodine (III) species,
which inhibited the undesired oxidation of electron-rich FGs.
In addition, the highly electrophilic a,b-unsaturated esters
(5ay and 5aa’) that can be challenging substrates for conven-
tional cross-coupling reactions were also compatible with the
current reaction conditions. The broad scope of FGs adopted
in the reaction provided a versatile platform for further
elaboration of the products and demonstrated the practic-
ability of the protocol.
Scheme 1. Background and the Morita–Baylis–Hillman (MBH) type
[3,3]-rearrangement of aryl iodanes. Tf2O=triflic anhydride.
Scheme 2. [3,3]-rearrangement of b-pyridinium silyl enol ethers devel-
oped by Wengryniuk (ref. [16]).
Next, the scope of aryl iodanes 1 was explored under the
optimum conditions (Scheme 3). para-Alkylated aryl iodanes
(5bb and 5cb) were slightly more productive than those
bearing para-halide substituents (5db–5gb). Impressively,
aryl iodanes 1 bearing functional groups including alkyl/aryl
halides (5db–5gb, 5hb, 5rb and 5vb), N-protected amines
Results and Discussion
With the MBH-type [3,3]-rearrangement hypothesis in
mind, we commenced the study by investigating the reaction
of PhI(OAc)2 1a with a,b-unsaturated carbonyl derivatives
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Table 1: Development of the reaction.
deiodinated coupling product 7
was determined from the reaction.
In contrast with reactions of other
aryl iodanes wherein Z-products
could not be obtained, the reaction
of thiophene iodane (1b’) afforded
an E/Z (96/4) mixture of 5b’b.
Entry[a]
Nu
Base
T [8C]
t [h]
Yield [%][b]
To deeply understand the reac-
tion mechanism and the E-selectiv-
ity of the reaction, we combined
DFT calculations (see SI8 for com-
putational details) and control ex-
periments to study the reactions of
1a with E-3c and Z-3c (Figure 2A).
1
2
3
4
5
6
7
8
2a
2b
2c
2d
2e
2 f
2g
2h
3a
3a
3a
3a
3a
3a
3a
3a
3a
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DBU
i-Pr2EtN
pyridine
4-methylpyridine
4-methylpyridine
4-methylpyridine
4-methylpyridine
4-methylpyridine
0
0
0
0
0
0
0
0
0
0
0
0
0
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
24
36
4a, 0[c]
4b, 0[c]
4c, 0[c]
4d, 0[c]
4e, 0[c]
4 f, 0[c]
4g, 0[c]
4h, 0[c]
5aa, 19
5aa, 16
5aa, 32
5aa, 39
5aa, 42
5aa, 58
5aa, 53
5aa, 71
5aa, 69
9
10
11
12
13
14
15
16
17
The overall mechanism of the
reaction
À10
À20
À10
À10
Figure 1 shows the energy pro-
file for the reaction with E-3c as
a substrate to afford E-5ac. The
reaction proceeds via sequential
four stages. Stage I undergoes elec-
trophilic assembly to generate the
precursors (EIM1 and EIM1’) for
subsequent MBH-like addition. To
start stage I, TMSOTf first activates
PhI(OAc)2 to give PhI(OTf)OAc[19]
via a SN2 transition state TS1.
Further activation of PhI(OTf)OAc
via TS2 gives PhI(OTf)2. The acti-
vation to give PhI(OTf)OAc is ex-
ergonic by 4.3 kcalmolÀ1 and that to
give PhI(OTf)2 is endergonic by
2.2 kcalmolÀ1. The energetic results
agree with the observation of PhI-
(OTf)OAc instead of PhI(OTf)2
[a] Reactions were performed on 0.5 mmol scale; 2a–2e and 3a (2.0 equiv), TMSOTf (2.0 equiv) and
bases (2.0 equiv) were used. [b] Isolated yield. [c] Volatile 2a (19%), 2b (55%) and 2d (85%) were
detected by crude 1H NMR spectroscopy whereas 2c (83%), 2e (47%), 2 f (63%), 2g (77%), and 2h
(51%) were recovered after the reaction.
(5ib and 5sb–5ub), esters (5ib and 5pb–5rb), ethers (5lb– reported by Dutton and Shafir and our NMR studies.[19,20]
5ob), and nitriles (5ob) were all suitable for the reaction.
Even highly reactive benzylic chlorides (5hb) and a,b-
unsaturated esters (5qb) that can be problematic FGs for
conventional arylation reactions could be tolerated in the
reaction. Aryl iodane 1j with electron withdrawing groups
(benzoyl group) failed to furnish any desired products 5jb
under optimum conditions. This was probably due to the
relatively low nucleophilicity of this electron-poor substrate,
which made the electrophilic activation of 1j with TMSOTf
more difficult. However, raising the activation temperature
from À788C to rt, 1j still afforded 5jb albeit in a low yield
(33%). Remarkably, meta-substituted aryl iodanes exclusive-
ly produced less hindered products (5kb–5wb) demonstrating
an excellent regioselectivity. It is also impressive that steri-
cally hindered substrates furnished intriguing polysubstituted
arenes (5xb–5zb) without loss of efficiency. In addition to
phenyl iodanes, the method could also be applicable to
naphthalene and thiophene iodanes (1a’ and 1b’) albeit giving
relatively low yields (5a’b and 5b’b). It should be noted that in
the synthesis of 5a’b, trace amount of ipso substituted
After the activation, E-3c undergoes substitutions with
PhI(OTf)OAc or PhI(OTf)2. Substitution with PhI(OTf)OAc
can take place via either TS3 or TS4, leading to EIM1’ or
EIM1, respectively and that with PhI(OTf)2 via TS5, giving
EIM1.[21] Because OTfÀ is a much greater leaving group than
OAcÀ, TS4 is much higher than TS3 and TS5. The formation
of EIM1 is kinetically less favorable but thermodynamically
more favorable than that of EIM1’. Both EIM1 and EIM1’ are
accessible. We first consider more stable EIM1 to start stage
II. As illustrated by (R)ETS6 or (S)ETS6, the base
4-methylpyridine (denoted as Py) can attack EIM1 from
either side of the alkene plane to undergo MBH-like
nucleophilic addition, giving (R)IM2 and (S)IM2, respective-
À
ly. Stage III from IM2 to IM4 forms a C C bond via
dearomative [3,3]-sigmatropic rearrangement through TS7,
followed by rearomatization via a negligible barrier (TS8, not
À
shown in Figure 1A, see Figure S1). After forming the C C
bond, a stepwise E1cb elimination (stage IV) takes place
through deprotonation via TS9, followed by Py elimination
via TS10, affording the final product E-5ac. Compared to
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Scheme 3. Reaction scope. [a] Reactions were performed with 1 (0.5 mmol), (E)-a,b-unsaturated oxazolines 3 (2.0 equiv), TMSOTf (2.0 equiv) and
4-methylpyridine (2.0 equiv). For all cases except 5b’b, Z-isomeric products were not observed. [b] 4-Methylpyridine (2.5 equiv), À78 to 108C,
36 h. [c] 1.0 mmol scale reaction. [d] Products (5av and 5az) were contaminated by trace amount of inseparable unknown compounds.
[e] TMSOTf was added at 08C (5db) or rt (5jb). [f] a-OTf-substituted a,b-unsaturated oxazoline 6 was obtained in 3% yield. [g] Inseparable ipso-
coupling product 7 was obtained in 3% NMR yield as a mixture with 5a’b.
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Figure 1. (A) Free energy profile of the reaction with E-3c as a substrate. B) (R)-Pathway to form E-5ac. C) (S)-Pathway to form E-5ac.
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EIM1, EIM1’ is less favorable to undergo MBH-like addition.
can be applied to the (S)-pathway (see Figure 1C), which
Furthermore, the addition products (R)/(S)IM2’ cannot
undergo rearrangements because of the much higher barriers
than those of IM2. Thus, the kinetically accessible EIM1’
would convert back to EIM1 for rearrangement. The much
higher TS7’ than TS7 can be attributed to the poorer leaving
group OAcÀ than OTfÀ, because the rearrangement forms
shows that E-5ac is a preferred product.
Understanding the reaction of Z-3c
Figure 2B considers the stage II of the reaction with Z-3c
as a substrate. Because the MBH-like addition of Py converts
the sp2 hybridized carbon to the sp3 hybridized carbon, the
stage II of Z-3c merges to that of E-3c at (R)IM2 and (S)IM2,
respectively. Therefore, the configuration of 3c cannot affect
the selectivity of the reaction. Indeed, under the standard
experimental conditions, no matter which configuration 3c
adopts, the reactions afforded E-5ac with comparable yields
[see Eq. (1) and Eq. (2) in Figure 2A]. Taking the results of
both E-3c and Z-3c together, the reaction prefers E-product
(E-5ac).
+
À
=
a formal I C double bond, which dissociates the axial OTf /
OAcÀ group, as shown by the I···C and O···I distances (see
Figure S2).
Examining the energy profile, as the reaction proceeds,
the system becomes more and more stable with an overall
exergonicity of 94.4 kcalmolÀ1. The rate determining step lies
at the deprotonation of IM4, with a barrier of 12.9 and
13.9 kcalmolÀ1 for (R)- and (S)-pathway, respectively. The
favorable energetics rationalizes why the reaction could
proceed smoothly, thus corroborating our strategy using
MBH-like addition to generate a reactive rearrangement
precursor (i.e. IM2). Supporting the mechanism, we were able
to observe the cationic IM4 (435) by mass spectrometry.
Unfortunately, we were not able to further confirm IM4 with
NMR spectrum even after great efforts.[22]
It should be noted that we used OTf group throughout the
calculations of the free energy profile. However, it is possible
that EIM1 and IM2 first substitute the axial OTf group with
3c or Py and the resultant intermediates then undergo MBH-
like additions or [3,3]-rearrangements. Using EIM1 as an
example, we considered the possibility. As detailed in Fig-
ure S1E in the supporting information (S54), it was found that
the substitutions are kinetically accessible, but the resultant
intermediates are less favourable to undergo MBH-like
addition than EIM1. On the other hand, no matter whether
these substitutions take place or not, stage III can only give
IM4 which we observed. As such, the E-selectivity of the
reaction, which is determined by stage IV, would not change.
Understanding the E-selectivity of the reaction
After grasping the reaction mechanism, we further under-
stand the E-selectivity of the reaction. Along the (R)-path-
way, all structures from (R)IM2 to (R)IM5 were optimized
with the conformations in which n-Pr and oxazoline groups
are in trans arrangement, thus giving E-5ac. To gain insight to
the E-selectivity, we further considered the cis-isomer of
trans-(R)IM5. As illustrated in Figure 1B, the cis conforma-
tion (i.e. (RZ)IM5) of IM5 can lead to Z-5ac by crossing
(RZ)TS10. However, because (R)IM5 and (RZ)IM5 can
convert each other easily with a barrier (R)TS11 lower than
(R)TS10, E-5ac is lower than Z-5ac, and the barrier for the
reverse conversion of Z-5ac to (RZ)IM5) is not high
(11.3 kcalmolÀ1), the formation of E-5ac is preferred in terms
of both kinetics and thermodynamics, explaining the
E-selectivity of the reaction. Due to the conformation
convergence of IM5 to (R)IM5, the conformations of the
intermediates and transition states from IM2 to IM4 cannot
affect the E-selectivity of the reaction, although they may
have multiple conformations, respectively. Similar discussion
Figure 2. A) Control experiments and B) profile for stage II of Z-3c.
Comparison of the Z-selective sulfonium and E-selective
iodonium MBH-type [3,3]-rearrangements
Intriguingly, as the present reaction of aryl iodanes prefers
E-product, the reaction of aryl sulfoxide (Scheme 1B) favours
the Z-product. Comparing the two reactions (Figure 3), they
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Figure 3. A comparison between Z-selective sulfonium and E-selective iodonium MBH-type [3,3]-rearrangement reactions.
proceed similarly, but their E1cb-elimination stages differ
significantly; the reaction of aryl sulfoxide requires an
external (i.e. K2CO3) to enable the E1cb elimination, while
the present reaction can take place without an external base.
The external base-free E1cb elimination can be attributed to
the N-protonation of IM4 with HOTf at oxazoline moiety.
Supportively, in the absence of the N-protonation, the
deprotonation of (S)IM4 has a barrier of 27.0 kcalmolÀ1,
which is much higher than the 13.9 kcalmolÀ1 from (S)IM4 to
(S)TS9. The significantly decreased deprotonation barrier is
due to the electron-buffering effect of the N-protonated
The product 8 could also be readily converted to intriguing
arylcyclopropanes (12a and 12b) and a-aryl-b-amine ester
(13) via conventional cyclopropanation and Michael addition,
respectively. In addition, the reduction of 8b afforded
valuable 2-aryl allylic alcohol 14. Encouraged by the success
of the MBH-type [3,3]-rearrangement, we attempted to
examine the possibility of corresponding [5,5]-rearrangement
by employing 1,3-diene-1-oxazoline 3c’ (Scheme 4C). Excit-
À
ingly, the reaction indeed afforded para-C H functionalized
product 15 (31% yield) with ortho-functionalized product
5ac’ (36% yield).[23] Although suffering from a poor selectiv-
ity, this preliminary result demonstrated the feasibility of
applying the current protocol for developing MBH-type [5,5]-
rearrangement reactions.
oxazoline. The effect enables the formation of the (oxazoli-
a
=
ne)C C double bond to stabilize the electrons resulted from
the deprotonation, as indicated by the shortened (oxazoli-
ne)C-Ca bond length from 1.50 to 1.43 to 1.36 Š in (S)IM4,
(S)TS9, and (S)IM5, respectively (for more detailed structural
evolutions see Figure S3). More importantly, the electron- Conclusion
buffering effect through deprotonation/protonation of oxazo-
line also makes Py-elimination reversible. As such, the
E-selectivity of the reaction is controlled kinetically and
thermodynamically at the Py-elimination and the kinetics
(selectivity) of other processes does not affect the
E-selectivity of the reaction. In contrast, the E1cb-elimination
in the reaction of aryl sulfoxides is prompted by K2CO3 and is
irreversible. The Z-selectivity of the reaction is jointly
controlled by the kinetics of the diastereoselective MBH
addition and cis-selective Pc-elimination elimination.[15]
To our delight, the method followed by hydrolysis of
oxazolines could be used for gram-scale synthesis of a-aryl
a,b-unsaturated carboxylic acids 8a and 8b with synthetically
useful yields (Scheme 4A). The remaining iodide atom
allowed for elaborating alkenes with a boryl group (9) or
vinyl ester moieties (10a and 10b), and incorporating an
alkynyl group into phenyl ring (11a and 11b) (Scheme 4B).
In summary, the incorporation of MBH reaction into the
rearrangement process forged [3,3]-rearrangement of aryl
iodanes with a,b-unsaturated oxazolines. Experimental and
computational mechanistic studies revealed that the trans-
formation involves the assembly of both coupling partners,
MBH-like addition triggered [3,3]-rearrangement, and E1cb
elimination to give the final products. The reaction allows for
the mild synthesis of a wide variety of valuable a-aryl
a,b-unsaturated oxazolines in a redox-neutral manner. In
addition to the excellent chemo- and regioselectivity, the
reaction showed a remarkable E-selectivity. The formation of
E-product is both kinetically and thermodynamically fav-
oured and is probably due to the final trans-b-H-elimination.
The stereocontrol of the reaction is different with MBH-type
sulfur(IV)-rearrangement, previously developed in our labo-
ratory, wherein the diastereoselective MBH-like addition and
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Zhejiang Province (LR20B020001). Z.-X.W. acknowledges
the support of NSFC-21773240.
Conflict of interest
The authors declare no conflict of interest.
Keywords: arylation ·hypervalent iodine ·Morita–Baylis–
Hillman reaction ·rearrangement ·vinylation
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Scheme 4. A) Gram-scale reactions. B) Synthetic utility. (1) K2CO3, MeI,
DMF; then Pd(OAc)2 (5 mol%)/ligand (7.5 mol%), B2(Pin)2, CsOAc,
THF. (2) K2CO3, MeI, DMF; then Pd(OAc)2 (5 mol%)/ligand
(10 mol%), ethyl acrylate, CsOAc, THF. (3) Pd(PPh3)4 (5 mol%), CuI
(10 mol%), phenylacetylene, toluene/Et3N. (4) (CH3)3SOI, NaH,
DMSO. (5) N,N-dibenzylamine, DBU, THF. (6) K2CO3, MeI, DMF; then
DIBAL-H, THF. C) Attempts of MBH-type [5,5]-rearrangement.
final cis-selective elimination determines the Z-selectivity of
the reaction. As a result, these two MBH type rearrangement
reactions complement each other allowing for the synthesis of
Z- or E-a-aryl a,b-unsaturated carbonyls on demand. Further
exploration of MBH-type rearrangement reactions is cur-
rently under way in our laboratory.
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Acknowledgements
B.P. thanks the Key Laboratory of the Ministry of Education
for Advanced Catalysis Materials at Zhejiang Normal Uni-
versity, NSFC-22071219, Natural Science Foundation of
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Manuscript received: January 12, 2021
Revised manuscript received: February 25, 2021
Accepted manuscript online: February 28, 2021
Version of record online: April 7, 2021
11422 www.angewandte.org
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Angew. Chem. Int. Ed. 2021, 60, 11414 –11422