Palladium-catalyzed diastereoselective synthesis of homoaldol equivalent products

Article abstract of DOI:10.1016/j.tetlet.2017.04.064

A palladium-catalyzed reaction of easily accessible 3-(pinacolatoboryl)allyl acetates and aldehydes provides facile access to synthetically useful homoaldol equivalent products with high diastereoselectivity. The reaction presumably proceeds via allylation of aldehydes with α-acetoxy allylboronates that produced in situ by reductive elimination from allylic gem-palladium/boryl intermediates.

Full text of DOI:10.1016/j.tetlet.2017.04.064

Accepted Manuscript
Palladium-Catalyzed Diastereoselective Synthesis of Homoaldol Equivalent
Products
Yoshikazu Horino, Miki Sugata, Tetsu Sugita, Ataru Aimono, Hitoshi Abe
PII:
S0040-4039(17)30517-8
DOI:
http://dx.doi.org/10.1016/j.tetlet.2017.04.064
TETL 48856
Reference:
Tetrahedron Letters
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Received Date:
Revised Date:
Accepted Date:
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13 April 2017
18 April 2017
Please cite this article as: Horino, Y., Sugata, M., Sugita, T., Aimono, A., Abe, H., Palladium-Catalyzed
Diastereoselective Synthesis of Homoaldol Equivalent Products, Tetrahedron Letters (2017), doi: http://dx.doi.org/
10.1016/j.tetlet.2017.04.064
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Palladium-Catalyzed Diastereoselective Synthesis of Homoaldol Equivalent Products
Yoshikazu Horino∗, Miki Sugata, Tetsu Sugita, Ataru Aimono, and Hitoshi Abe
Department of Applied Chemistry, Graduate School of Science and Engineering, University of Toyama, Gofuku, Toyama 930-8555, Japan
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
A palladium-catalyzed reaction of easily accessible 3-(pinacolatoboryl)allyl acetates and
aldehydes provides facile access to synthetically useful homoaldol equivalent products with high
diastereoselectivity. The reaction presumably proceeds via allylation of aldehydes with α-
acetoxy allylboronates that produced in situ by reductive elimination from allylic gem-
palladium/boryl intermediates.
Available online
2016 Elsevier Ltd. All rights reserved
.
Keywords:
Allylation
Homoaldol equivqlent reaction
Palladium catalysis
Allylpalladium
———
∗ Corresponding author. Tel.: +81-76-492-5313; fax: +81-76-492-5131; e-mail: horino@eng.u-toyama.ac.jp

2
Tetrahedron
Introduction
Supplementary Material). It was found that both the electronic
nature and the amount of the phosphine ligand play an important
−4). However,
Devising synthetic strategies for constructing molecular
role in improving the yield of 3aa (entries 2
a non-
complexity and diversity from simple reagents is an important
subject in organic synthesis. In particular, catalytic synthetic
strategies can offer enormous advantages for such purposes
because they can individually generate several intermediates that
react in different manners from the same reagent. Allylpalladium
species are one representative example. For example, π-
allylpalladium species are generally recognized to serve as
synthetically useful electrophilic allylating agents toward many
nucleophiles.1 In contrast, σ-allylpalladium species possessing
ligands that donate electrons acts as nucleophilic allylating agents
toward electrophiles.2 Moreover, umpolung reaction of π-
allylpalladium alters its reactivity pattern to nucleophilic.3,4
Fillion and our recent studies on allylic gem-heterobimetallic
species revealed individually that the distinct reactivities of
allylic gem-palladium/metalloid species cannot be reached by
hitherto reported allylpalladium species.5-8 For example, the
allylic gem-palladium/boryl species take part in the
stereoselective cyclopropanation of strained alkenes,6 carbene
dimerization reaction,7 and three-component coupling reaction
with aldehydes and triorganoboranes (Scheme 1).8 During the
course of our study of three-component coupling reactions, a
palladium-catalyzed methodology for diastereoselective synthesis
of homoaldol equivalent products was discovered during a
control reaction attempt in the absence of a triorganoborane; the
palladium-catalyzed reaction of 3-(pinacolatoboryl)allyl acetates
1 and aldehydes 2 gave anti-(Z)-δ-hydroxy vinyl acetates 3 with
high levels of diastereoselectivity and alkene stereocontrol.8a
negligible amount of 4a was also obtained. The enhancement of
the Brønsted base character of the carbon atom between the
palladium and the pinacolatoboryl group in allylic gem-
palladium/pinacolatoboryl
species
presumably
induces
protodeboronation to form 4a.5,6 However, addition of MS 4A
to prevent the formation of 4a by residual H2O failed (entry 6).7
Although the catalyst loading could be reduced to 5 mol%
without significant loss of catalytic activity, we were pleased to
find that use of an excess amount of 2a (3 equiv to 1a) improved
the yield of 3aa (entry 7). Besides the monodentate phosphine
ligand, use of bidentate phosphine ligands also efficiently
promoted the present reaction (entries 8−12). Among them,
Xantphos16 exhibited the comparable results with (p-CF3C6H4)3P
(entries 7 and 12). In all cases, the relative configuration of the
two newly formed stereogenic centers is anti (anti/syn >20/1),
and the Z-isomer was the primary product.
Table 1
Optimization of reaction conditionsa
OH
Ph
Pd(OAc)2
OAc
Ligand
Ph
+
OAc 3aa
OAc 4a
+
PhCHO
Ph
B(pin)
toluene, 70 ºC
1a
2a
Ph
Pd(OAc)2
(mol%)
Ligand
(mol%)
3aa
(%)
3aa
(Z/E)
4a
(%)
Entry
Since the pioneer work of Nakamura and Kuwajima on the
catalytic homoaldol reactions,9,10 generation of homoenolates and
homoenolate equivalents using transition-metal catalysts and
organocatalysts have emerged as strategically different
approaches.11-13 In addition, catalytic asymmetric versions have
also been developed.14 Although significant progress has been
made in this area, the diastereoselective synthesis of homoaldol
equivalent products by catalytic processes still needs to be
explored.15 Herein, we report a palladium-catalyzed methodology
for the diastereoselective synthesis of homoaldol equivalent
products.
1
10
10
10
10
5
Ph3P (20)
60
53
71
77
64
38
84
33
60
62
61
83
7/1
2
2
(p-MeOC6H4)3P (20)
(p-CF3C6H4)3P (20)
(p-CF3C6H4)3P (30)
(p-CF3C6H4)3P (15)
(p-CF3C6H4)3P (15)
(p-CF3C6H4)3P (15)
DPEphos (10)
8.2/1
9/1
19
0
3
4
9.4/1
10/1
8/1
7
5
19
38
12
4
6b
7c
8
5
5
9/1
OAc
10
10
10
5
10/1
8.3/1
10/1
9.6/1
10/1
R1
B(pin)
1
9
DPPPent (10)
14
13
13
11
X
X
Pd(0)
this work
R2CHO
H
10
11
12c
Xantphos (10)
X
X
R1
(pin)
B
OH
ref 6
R1
2
Xantphos (5)
O
R2
OH
LnPd
R2CHO
R1
5
Xantphos (5)
OAc
O
Me
R2
(R3)3B
aReaction conditions: 1a (0.5 mmol), 2a (1.2 mmol), Pd(OAc)2, and
ligand [DPEphos = 2,2’-bis(diphenylphosphino)diphenyl ether, DPPPent
=
3
R1
R3
ref 7
ref 8
R1
1,5-bis(diphenylphosphino)pentane,
Xantphos
=
4,5-
R1
Bis(diphenylphosphino)-9,9-dimethylxanthene] in toluene (2 mL) at 70
°C for 1–6 h.
Scheme 1. Distinct reactivities of allylic gem-palladium/boryl
species.
bMS 4A (500 mg) was used.
cPhCHO (3 equiv) was used.
Results and discussion
Having determined the optimal conditions (Table 1, entry 12),
the substrate scope with regard to aldehydes 2 was first explored
by reactions with 1a (Table 2). It was found that a broad range of
aromatic aldehydes was tolerated. Indeed, the reaction proceeded
without being influenced by the electronic nature of the
We initially optimized the reaction conditions for the
palladium-catalyzed reaction of (1-phenyl-3-pinacolatoboryl)allyl
acetate (1a) as a model substrate with benzaldehyde (2a) by
evaluating various ligands (Table 1). The Pd(OAc)2/PPh3
catalytic system provided a anti-homoaldol equivalent product
3aa in 60% yield, accompanied by 4a (entry 1). The relative
stereochemistry of 3aa was determined to be anti by
derivatization to give a literature known material (see the
substituent
to
afford
3ab−3ag.
Unfortunately,
4-
bromobenzaldehyde and 4-hydroxybenzaldehyde did not take
part in the reaction. Altough 2-thiophenecarboxaldehyde could be
transformed effectively into its corresponding products 3ah in

70% yield with excellent diastereoselective fashion, the use of 3-
and 4-pyridinecarboxyaldehyde resulted in no reaction.
Additionally, α,β-unsaturated aldehydes also underwent the
current homoaldol equivalent reaction to give 3ai and 3aj,
respectively. Although substantially less reactive aliphatic
aldehydes also took part in the palladium-catalyzed homoaldol
equivalent reaction, the desired products were isolated in lower
yield. For example, 3ak and 3am were obtained in 55% and 56%
yields, respectively. However, this problem was overcome when
(p-CF3C6H4)3P was employed as a ligand, giving 3ak and 3am in
65% and 66% yields, respectively. On the other hand, a moderate
and the C–Br bond remained intact. This protocol tolerated a
heterocycle-substituted substrate such as 2-thienyl, and provided
a corresponding homoaldol equivalent product 3ja in 75% yield.
Unfortunately, only trace amounts of desired product were
obtained when alkyl-substituted substrates such as methyl- and
cyclohexyl-substituted substrates were applied. Moreover, use of
ketones such as acetophenone and 1,2-cyclohexanedione instead
of aldehydes did not produce the desired homoaldol equivalent
products.
Table 3
Substrate Scopea
isolated
yield
of 3al
was still
observed with
cyclohexanecarboxaldehyde. In all cases, the excellent
diastereoselectivities were observed for all aldehydes examined.
OH
Ph
Pd(OAc)2 (5 mol%)
OAc
Xantphos (5 mol%)
R1 OAc
3
4
R1
B(pin)
PhCHO
+
+
toluene, 70 ºC
R1
Table 2
Screening of aldehydesa
1a
2a
OAc
OAc
OH
HO
Ph
HO
HO
Ph
OAc
OAc
R2
Pd(OAc)2 (5 mol%)
OAc
Xantphos (5 mol%)
Ph
MeO
Ph
+
OAc
3
OMe
R2CHO
+
Ph
B(pin)
toluene, 70 ºC
OMe
1a
2
Ph
OAc 4a
3ba: 80%
Z/E = 9/1, dr >20/1b
4b: 10%
3ca: 75%c
Z/E = 2.2/1, dr 81/19b
4c: 4%
3da: 87%c
Z/E = 8.3/1, dr >20/1b
4d: trace
OH
MeO
OH
OH
HO
OAc
Ph
HO
OAc
Ph
HO
OAc
Ph
Ph OAc
Ph OAc
Ph OAc
MeO
Me2N
3ac: 72%
Z/E = 9/1, dr >20/1b
4a: 0%
Br
3ab: 80%
3ad: 60%
O
Z/E = 9.8/1, dr >20/1b
4a: 14%
OH
Z/E = 7/1, dr >20/1b
4a: 0%
OH
O
CO2Me
OH
3ea: 74%
Z/E = 9.3/1 dr >20/1b
4e: 6%
3fa: 66%
Z/E = 8.7/1, dr >20/1b
4f: 4%
3ga: 65%
Z/E = 6.6/1, dr >20/1b
4g: 5%
Ph OAc
Ph OAc
Ph OAc
X
F3C
O2N
HO
OAc
Ph
HO
OAc
Ph
HO
OAc
3ae (X = CO2Me): 86%
Z/E = 9.5/1, dr >20/1b
4a: 6%
3af: 73%
Z/E = 11/1, dr >20/1b
4a: 14%
3ag: 86%c
Z/E = 11/1, dr >20/1b
4a: 0%
Ph
S
Br
OH
OH
OH
Br
3ha: 60%
3ia: 51%
3ja: 75%
Z/E = 13/1, dr >20/1b
4j: 18%
Ph
Z/E = 7.8/1, dr >20/1b Z/E = 11.5/1, dr >20/1b
S
Ph OAc
Ph OAc
Ph
Ph OAc
3aj: 50%
4h: 16%
4i: 10%
3ah: 70%
Z/E = 10.6/1, dr >20/1b
4a: 10%
3ai: 78%
Z/E = 8.4/1, dr >20/1b
4a: 0%
aConditions: 1a (0.5 mmol), 2a (1.5 mmol), Pd(OAc)2 (5 mol%), and
Xantphos (5 mol%) in toulene (2 mL) at 70 °C for 1-3 h.
Z/E = 9.8/1, dr >20/1b
4a: 0%
bThe relative stereoconfiguration was determined by analogy.
c(p-CF3C6H4)3P (15 mol%) was used instead of Xantphos.
OH
OH
OH
Ph
Ph OAc
Ph OAc
Ph OAc
3ak: 65%c
Z/E = 7.3/1, dr >20/1b
4a: 7%
3al: 40%c
Z/E = 5.5/1, dr >20/1b
4a: 15%
3am: 66%c
Z/E = 7/1, dr >20/1b
4a: 14%
To gain insights into the reaction mechanism, a chirality
transfer experiment using (R)-1a was first performed under
optimum reaction conditions (Scheme 2a). Unlike in the case of
our previous work, 3aa was produced as a racemic form.8a In
addition, the use of 1m possessing stereogenic centers onto the
boronic ester moiety resulted in no conversion, and 1m was
recovered (Scheme 2b).17
aReaction conditions: 1a (0.5 mmol), 2a (1.5 mmol), Pd(OAc)2 (5 mol%),
and Xantphos (5 mol%) in toluene (2 mL) at 70 °C for 1–3 h.
bThe relative stereoconfiguration was determined by analogy.
c (p-CF3C6H4)3P (15 mol%) was used instead of Xantphos.
3aa: 71% yield
Z/E = 10/1, 0% ee
Pd(OAc)2 (5 mol%)
Xantphos (5 mol%)
OAc
Next, we examined the substrate generality of the reaction. A
variety of aryl-substituted substrates were subjected to the
reaction conditions (Table 3). In general, both substrates with
electron-withdrawing and electron-donating substituents on
aromatic ring took part in the reaction to produce the
corresponding products 3ba−3ia in good to high yield. Although
use of Xantphos as a ligand gave 3ca and 3da in 32% and 42 %
yields, respectively, changing Xantphos to (p-CF3C6H4)3P
improved the chemical yield. The substrate bearing a methoxy-
substituent at the ortho position on the aromatic ring gave 3ca
with moderate diastereoselectivity (dr = 81/19). Notably, o-
bromo-, m-bromo-, and p-bromo-substituted-phenyl substrates
were also compatible with the present reaction conditions,
providing 3ga−3ia in 65%, 60%, and 51% yields, respectively,
+
PhCHO
+
(a)
Ph
B(pin)
toluene, 70 ºC
4a: 7%
2a
(R)-1a (90% ee)
Scheme 2. Chirality transfer reactions.
A preliminary reaction mechanism is depicted in Scheme 3.
First, oxidative addition of 1 to a palladium complex forms an η3-
allylpalladium intermediate A. Then, reductive elimination from
allylic gem-palladium/boryl intermediate A′ (for simplicity,

4
Tetrahedron
another η1-allyl form is not depicted) would produce α-acetoxy
2. For selected reviews of carbonyl allylation via umpolung of π-
allylpalladium, see: (a) Zanoni, G.; Pontiroli, A.; Marchetti, A.;
Vidari, G. Eur. J. Org. Chem. 2007, 3599–3611; (b) Marshall, J.
A. Chem. Rev. 2000, 100, 3163–3186; (c) Tamaru, Y. Eur. J. Org.
Chem. 2005, 2647–2656; (d) Yus, M.; González-Gómez, J. C.;
Foubelo, F. Chem. Rev. 2011, 111, 7774–7854.
allylboronate
B.
This
step
presumably
involves
isomerization through η3-allylpalladium complex, which may
account for the observed no chirality transfer as shown in
Scheme 2a. Finally, allylboration of aldehyde via two competing
chair-type transition states C and D takes place. Since the
acetoxy substituent is a polar group, allylboration proceeds
predominately via transition state D to give (Z)-anti-3.15c, 18, 19
3. σ-Allylpalladium-mediated nucleophilic allylation reactions, see:
(a) Kurosawa, H.; Urabe, A. Chem. Lett. 1985, 1839–1840; (b)
Kurosawa, H.; Ogoshi, S. Bull. Chem. Soc. Jpn. 1998, 71, 973–
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Soc. 1996, 118, 6641–6647; (d) Nakamura, H.; Nakamura, K.;
Yamamoto, Y. J. Am. Chem. Soc. 1998, 120, 4242–4243; (e)
Fernandes, R. A.; Stimac, A.; Yamamoto, Y. J. Am. Chem. Soc.
2003, 125, 14133–14139; (f) Soiln, N.; Kjellgre, J.; Szabó, K. J.
Angew. Chem. Int. Ed. 2003, 42, 3656–3658; (g) Solin, N.;
Kjellgren, J.; Szabó, K. J. J. Am. Chem. Soc. 2004, 126, 7026–
7033; (h) Barczak, N. T.; Grote, R. E.; Jarvo, E. R.
Organometallics 2007, 26, 4863–4865; (i) Shaghafi, M. B.; Kohn,
B. L.; Jarvo, E. R. Org. Lett. 2008, 10, 4743–4746; (j) Mita, T.;
Higuchi, Y.; Sato, Y. Chem. Eur. J. 2015, 21, 16391–16394.
R1
LnPd
R1
OAc
B(pin)
B(pin)
OAc
PdLn(0)
-PdLn(0)
PdLn(0)
R1
B(pin)
LnPd
OAc
1
A
A'
OH
B(pin)
OAc
R2
H
O
R1
OAc
R2
4. σ-Allylpalladium-mediated enantioselective carbonyl allylation
reactions, see: (a) Zanoni, G.; Gladiali, S.; Marchetti, A.;
Piccinini, P.; Tredici, I.; Vidari, G. Angew. Chem. Int. Ed. 2004,
43, 846–849; (b) Zhu, S.-F.; Yang, Y.; Wang, L.-X.; Zhou, Q.-L.
Org. Lett. 2005, 7, 2333–2335; (c) Howell, G. P.; Minnaard, A. J.;
Ferigna, B. L. Org. Biomol. Chem. 2006, 4, 1278–1283; (d)
Onomura, O.; Fujimura, N.; Oda, T.; Matsumura, Y.; Demizu, Y.
Heterocycles 2008, 76, 177–182; (e) Wang, W.; Zhang, T.; Shi,
M. Organometallics 2009, 28, 2640–2642; (f) Qiao, X.-C.; Zhu,
S.-F.; Zhou, Q.-L. Tetrahedron Asymmetry 2009, 20, 1254–1261;
(g) Jiang, J.-J.; Wang, D.; Wang, W.-F.; Yuan, Z.-L.; Zhao, M.-
X.; Wang, F.-J.; Shi, M. Tetrahedron Asymmetry 2010, 21, 2050–
2054; (h) Qiao, X.-C.; Zhu, S.-F.; Chen, W.-Q.; Zhou, Q.-L.
Tetrahedron Asymmetry 2010, 21, 1216–1220; (i) Zhu, S.-F.;
Qiao, X.-Q.; Zhang, Y.-Z.; Wang, L.-X.; Zhou, Q.-L. Chem. Sci.
2011, 2, 1135–1140; (j) Yus, M.; González-Gómez, J. C.;
Foubelo, F. Chem. Rev. 2011, 111, 7774–7854; (k) Tsukamoto,
H.; Kawase, A.; Doi, T. Chem.Commun. 2015, 51, 8027–8030.
5. Pioneering works for the cyclopropanation of strained alkenes and
R1
(E)-3
C
R1
B(pin)
OAc
R2CHO
B
OH
B(pin)
R1
R2
O
OAc
R2
R1
(Z)-3
D
OAc
Scheme 3. A plausible reaction path.
To evaluate the utility of the homoaldol equivalent products
obtained in this study, 3ga was hydrolyzed under mildly basic
conditions to provide the corresponding formal homoaldol
product, which was subsequently converted into synthetically
useful trans-β,γ-diaryl-substituted-γ-butyrolactone 5 in 60% yield
followed by PCC oxidation (Scheme 4).20
carbene
dimerization by allylic gem-palladium/stannyl
intermediates, see: (a) Trépanier, V. É.; Fillion, E.
Organometallics 2007, 26, 30–32. (b) Fillion, E.; Trépanier, V. É.;
Heikkinen, J. J.; Remorova, A. A.; Carson, R. J.; Goll, J. M.;
Seed, A. Organometallics 2009, 28, 3518–3531.
Br
K2CO3 (2 equiv)
PCC oxidation
CH2Cl2, r.t., 5 h
3ga
MeOH, 60 °C, 3 h
Ph
O
O
6. (a) Horino, Y.; Homura, N.; Inoue, K.; Yoshikawa, S. Adv. Synth.
Catal. 2012, 354, 828. (b) Horino, Y.; Takahashi, Y.; Kobayashi,
R.; Abe, H. Eur. J. Org. Chem. 2014, 7818–7822.
5 (60% for two steps)
7. Horino, Y.; Takahashi, Y.; Koketsu, K.; Abe, H.; Tsuge, K. Org.
Lett. 2014, 16, 3184–3187.
8. (a) Horino, Y.; Aimono, A.; Abe, H. Org. Lett. 2015, 17, 2824–
2827; (b) Horino, Y.; Aimono, A.; Minoshima, N.; Abe, H.
Tetrahedron Lett. 2016, 57, 3561–3564; (c) Horino, Y.; Sugata,
M.; Abe, H. Adv. Synth. Catal. 2016, 358, 1023–1028.
Scheme 4. Hydrolysis and oxidation of a homoaldol
equivalent product.
In summary, we have developed a palladium-catalyzed
methodology for the diastereoselective synthesis of anti-
homoaldol equivalent products, which provides access to a
variety of synthetically useful compounds. Furthermore, the
present methodology enhances the utility of allylic gem-
palladium/boryl species, making it attractive alternative to
various synthetic strategies.
9. Nakamura, E.; Aoki, S.; Sekiya, K.; Oshino, H.; Kuwajima, I. J.
Am. Chem. Soc. 1987, 109, 8056–8066.
10. First observation of
a homoenolate anion, see: Nickon, A.;
Lambert, J. L. J. Am. Chem. Soc. 1962, 84, 4604–4605.
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13. Burstein, C.; Glorius, F. Angew. Chem. Int. Ed. 2004, 43, 6205–
6208.
Acknowledgments
14. (a) Liang, T.; Zhang, W.; Krische, M. J. Am. Chem. Soc. 2015,
137, 16024–16027; (b) Čorić, I.; Müller, S.; List, B. J. Am. Chem.
Soc. 2010, 132, 17370–17373.
We thank Prof. Ryuta Miyatake (University of Toyama) for his
assistance with HRMS measurements. This work was financially
supported by the JSPS KAKENHI Grant Number JP15K05496.
15. Non-catalytic condition, see; (a) Sakami, S.; Houkawa, T.;
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2nd ed.; Wiley: Chichester, 2004.

17. (a) Cmrecki, V.; Eichenauer, N. C.; Frey, W.; Pietruszka, J.
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mixtures. When the reaction was conducted for prolonged reaction
time, it led to competitive protodeboronation to produce cinnamyl
benzoate. Although Pd-catalyzed isomerization of 7 to 6 was also
examined, decomposition of 7 was observed. Allylboronates are
known to participate in allyl–allyl cross-coupling with allyl
electrophiles, see: (a) Brozek, L. A.; Ardolino, M. J.; Morken, J.
P. J. Am. Chem. Soc. 2011, 133, 16778–16781; (b) Amanda, H.
L.; Morken, J. Org. Lett. 2014, 16, 2096–2099.
18. For carbonyl addition with α-hetero atom substituted
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Lett. 1983, 24, 3209; (b) Hoffmann, R. W.; Landmann, B. Angew.
Chem., Int. Ed. 1984, 23, 437; (c) Hoffmann, R. W.; Dresely, S.
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Landmann, B. Chem. Ber. 1986, 119, 2013; (f) Hoffmann, R. W.;
Dresely, S. Tetrahedron Lett. 1987, 28, 5303; (g) Hoffmann, R.
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Hoffmann, R. W.; Dresely, S.; Hildebrandt, B. Chem. Ber. 1988,
121, 2225; (i) Hoffmann, R. W.; Dresely, S. Synthesis 1988, 103;
(j) Hoffmann, R. W.; Dresely, S. Chem. Ber. 1989, 122, 903; (k)
Stürmer, R.; Hoffmann, R. W. Synlett 1990, 759; (l) Hoffmann, R.
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Supplementary Material
Supplementary material that may be helpful in the review process
should be prepared and provided as a separate electronic file.
That file can then be transformed into PDF format and submitted
along with the manuscript and graphic files to the appropriate
editorial office.
19. To figure out the process of isomerization of
1
to the
corresponding allylboronate by palladium catalysis, (1-phenyl-3-
pinacolatoboryl)allyl benzoate (6) was treated with a catalytic
amount of Pd(OAc)2 (5 mol%) and Xantphos (5 mol%) in toluene
at 70 °C for 3 h. However, (3-phenyl-1-pinacolatoboryl)allyl
benzoate (7) was not observed by NMR analysis of the crude

6
Tetrahedron
Homoaldol equivalent products can be synthesized
with high diastereoselectivity.
Pd complex promotes isomerization of 1-
alkenylboronates to generate allylboronates.
Reaction involves allylboration of aldehydes with
α-acetoxy allylboronates.