Enantioselective Allyl-, and Allenylboration of Aldehydes Catalyzed by Chiral Hydroxyl Carboxylic Acid

Article abstract of DOI:10.1055/s-0036-1588690

Asymmetric allylboration of aldehydes with allylboronic acid pinacol ester catalyzed by chiral hydroxyl carboxylic acid is described. This reaction provides synthetically useful homoallyl alcohols in high yield with good to high enantioselectivity. The pr

Full text of DOI:10.1055/s-0036-1588690

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© Georg Thieme Verlag Stuttgart · New York
2017, 28, A–E
letter
A
Y. Ota et al.
Letter
Synlett
Enantioselective Allyl-, and Allenylboration of Aldehydes Cata-
lyzed by Chiral Hydroxyl Carboxylic Acid
Yuya Ota
Yuji Kawato
Hiromichi Egami
Yoshitaka Hamashima*
School of Pharmaceutical Sciences, University
of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka
422-8526, Japan
hamashima@u-shizuoka-ken.ac.jp
Received: 17.11.2016
Accepted after revision: 19.12.2016
Published online: 08.02.2017
ids with an electrophilic fluorinating reagent, Selectfluor®
was achieved.6 Our synthetic procedure allows for not only
the fine-tuning of steric and electronic properties at the
3,3′-positions of 1 but also the incorporation of a hydrogen
bond donor adjacent to the carboxylic acid functionality
(Figure 1).
DOI: 10.1055/s-0036-1588690; Art ID: st-2016-u0775-l
Abstract Asymmetric allylboration of aldehydes with allylboronic acid
pinacol ester catalyzed by chiral hydroxyl carboxylic acid is described.
This reaction provides synthetically useful homoallyl alcohols in high
yield with good to high enantioselectivity. The present catalytic proto-
col was also examined in asymmetric allenylboration of aldehydes at el-
evated temperature to afford chiral homopropargyl alcohols with rea-
sonable asymmetric induction.
Ar
Ar
Ar
Ar
OH
CO2H
CO2H
OH
OH
OH
CO2H
Ar
CO2H
Key words Brønsted acid catalysis, chiral hydroxyl carboxylic acid, allyl-
boration, homoallyl alcohol, allenylboration, homopropargyl alcohol
Ar
Ar
Ar
1
2
3
4
t-Bu
t-Bu
Organic acids constitute one of the most fundamental
catalysts in organic chemistry. They are versatile because
they can serve as a precursor of an anionic phase-transfer
catalyst and as an anionic ligand of metal complexes in ad-
dition to functioning as a simple acidic promoter.1 Since the
first reports on binaphthol-derived chiral phosphoric acid
catalyzed asymmetric Mannich type reactions by Akiyama2a
and Terada,2b chiral phosphoric acid catalysis has pro-
gressed greatly in the last decade.3 In contrast, despite its
potential utility,4 chiral carboxylic acids bearing a 1,1-
binaphthyl framework have been less well explored, proba-
bly due to the limited availability of an efficient synthetic
method.4a In this context, we recently reported a cost-effec-
tive and concise synthetic method for the construction of
binaphthol-derived chiral dicarboxylic acids 1 (Figure 1).5
By using this procedure, we were also able to synthesize a
partially reduced hydroxyl carboxylic acid 2 on a gram scale
as a result of desymmetrization of the dicarboxylic acid
moiety. The corresponding carboxylate anion of 2 was
found to serve as a novel bifunctional anionic phase-trans-
fer catalyst, with which the first successful example of cata-
lytic asymmetric fluorolactonization of ene-carboxylic ac-
Ph
t-Bu
Ar =
Ph
t-Bu
Ph
t-Bu
a
b
c
d
t-Bu
Figure 1 Chiral carboxylic acids and BINOL derivatives
Asymmetric allylation of carbonyl compounds is a use-
ful and reliable carbon–carbon bond-forming reaction for
the preparation of chiral homoallyl alcohols.7 Therefore, the
development of catalytic variants is an important subject,
and several catalytic systems with organoboronates were
developed as a powerful method.8 However, potentially tox-
ic metal-based catalysts or additives were used to promote
the reaction efficiently in many cases. Meanwhile, the or-
ganocatalytic version of this reaction has gained attention
as a more environmentally benign synthetic strategy,9–11
ever since Schaus and co-workers first reported the asym-
metric allylboration of ketones catalyzed by chiral diols.10a
In 2010, Antilla and co-workers first reported the highly
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

B
Y. Ota et al.
Letter
Synlett
enantioselective allylboration of aldehydes catalyzed by a
binaphthol-derived chiral phosphoric acid.11a Although
high enantioselectivity was achieved, particularly with aro-
matic aldehydes (73–99% ee), reaction temperature and
catalyst loading need to be improved. Therefore, further in-
vestigation of more efficient organocatalysts is desirable. In
our continuing efforts to expand the utility of Brønsted acid
catalysts, we applied such catalysts to the asymmetric allyl-
boration of aldehydes (Equation 1). According to the prece-
dent examples, we expected that our carboxylic acid cata-
lysts would promote the reaction by enhancing the Lewis
acidity of the boron center through either of the following
two activation modes: (1) the formation of a mixed acid
anhydride with the boronate ester,12 or (2) the protonation
of its oxygen atom. In this light, an investigation of the ca-
talysis of 1 and 2 would offer fresh insight into the design of
new catalysts that could show highly efficient and intrigu-
ing reactivity for asymmetric allylboration. Herein, we de-
scribe catalytic asymmetric allyl-, and allenylboration of al-
dehydes using chiral hydroxyl carboxylic acids.
these results, the following presumptions regarding the re-
action mechanism can be drawn: (1) The ester exchange on
the boron with the catalyst may not be involved in this re-
action, providing a contrasting example of Schaus’ BINOL-
catalyzed enantioselective allylation of ketones;10a,10b (2) If
an ester exchange reaction occurs, it is an undesired process
for high asymmetric induction; (3) Activation by protona-
tion of the boronate oxygen is most likely, which is similar
to the mode of action proposed by Antilla in his pioneering
work on chiral phosphoric acid catalyzed allylboration of
aldehydes;11a (4) The acidity of BINOL catalyst 4a would be
insufficient to activate the boronate ester, and ester ex-
change process between 4a and 6b and 6c might be slug-
gish at –78 °C, thus resulting in no formation of the desired
product 7a; (5) Although the exact role of the alcohol func-
Table 1 Optimization of the Reaction Conditionsa
O
OH
cat. (10 mol%)
–78 °C, 24 h
B(OR)2
+
Ph
H
Ph
Ar
5a
6
7a
Brønsted acid catalyst
O
OH
1 or 2
OMe
O
B
Oi-Pr
O
B(OR')2
+
B
B
R
H
R
CO2H
O
6a
O
Oi-Pr
6c
6b
Equation 1 Asymmetric allylboration of aldehydes promoted by chiral
Brønsted acid catalysts
Ar
8 (methyl ether of 2a)
Initially, we set out to evaluate the various carboxylic
acid catalysts in the reaction of benzaldehyde (5a) with all-
ylboronic acid pinacol ester (6a) (Table 1). The reaction
with dicarboxylic acid 1a afforded the desired homoallyl al-
cohol 7a in excellent yield with moderate enantiomeric ex-
cess at –78 °C (entry 1). Assuming that the high reactivity
of the diacid catalyst affected the asymmetric induction
negatively, partially reduced hydroxyl carboxylic acids,
which are considered to be less acidic, were next examined.
To our delight, the use of hydroxyl carboxylic acid 2a result-
ed in significant improvements in the enantioselectivity, al-
beit with moderate chemical yield (entry 2). Phenol carboxylic
acid 3a also afforded the desired adduct 7a, but the enantio-
selectivity dropped considerably (entry 3). In contrast, al-
most no conversion occurred in the reactions with BINOL
catalyst 4a or without any catalysts (entries 4 and 5), thus
indicating that the carboxylic acid functionality is crucial to
promote the reaction. In addition, in the presence of cata-
lyst 2a, the reactions with other boronate esters 6b and 6c,
which are prone to ester exchange reaction, proceeded with
extremely low enantioselectivity (entries 6 and 7). It should
be noted that methylation of the hydroxyl group within 2a
led to a significant decrease in the efficiency of the reaction.
Thus, the reaction with 8 gave 7a in only 16% yield with a
marginal enantioselectivity (2% ee), which strongly indi-
cates that the co-presence of both the acid and the hydroxyl
group at the defined position is essential (entry 8). From
Entry Catalyst 6 (equiv)
Solvent
Yield (%)b ee (%)c
1
2
1a
2a
3a
4a
–
6a (1.1)
6a (1.1)
6a (1.1)
6a (1.1)
6a (1.1)
6b (1.1)
6c (1.1)
6a (1.1)
6a (1.1)
6a (1.1)
6a (1.1)
6a (2.0)
6a (2.0)
6a (2.0)
6a (2.0)
6a (2.0)
6a (2.0)
6a (2.0)
6a (2.0)
CH2Cl2
98
43
43
<5
<5
27
99
16
48
27
40
73
54
84
58
80
92
<5
58
60
77
34
–
CH2Cl2
3
CH2Cl2
4
CH2Cl2
5
CH2Cl2
–
6
2a
2a
8
CH2Cl2
10
20
2
7
CH2Cl2
8
CH2Cl2
9
2b
2c
2d
2d
2d
2d
2d
2d
2d
2d
2d
CH2Cl2
63
86
85
85
83
62
76
69
72
–
10
11
12
13
14
15
16
17
18
19
CH2Cl2
CH2Cl2
CH2Cl2
toluene
hexane
hexane/CH2Cl2 (1:5)
hexane/CH2Cl2 (1:1)
hexane/CH2Cl2 (5:1)
THF
Et2O
54
a Compound 5a (0.05 mmol, 0.2 M).
b Isolated yield.
c Determined by HPLC analysis using a chiral stationary phase.
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C
Y. Ota et al.
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tionality of 2a has yet to be elucidated, hydrogen bonding
with the adjacent carboxylic acid is presumed to play an
important role in the transition state.13
Table 2 Effect of Protic Additivesa
2d (10 mol%)
O
OH
O
B
additives
+
We next examined the effect of 3,3′-substitution pat-
terns of the binaphthyl core of 2. Bulky substituents ap-
peared to be important to achieve high enantioselectivity,
and 2d was identified as the catalyst of choice, although the
yield remained moderate (entries 9–11). When the reaction
was run using 2 equivalents of 6a, the yield was improved
to 73% (entry 12). Whereas the use of toluene as solvent
showed marginal differences in the outcome of the reac-
tion, higher conversion was notable in hexane at the ex-
pense of the enantioselectivity (entries 13 and 14). The
combination of hexane and CH2Cl2 in different ratios was
then employed as the solvent (entries 15–17). Whereas a
slight loss in the enantioselectivity was detected in hex-
ane/CH2Cl2 (5:1), the yield was increased to 92%. While re-
action in tetrahydrofuran (THF) barely afforded the desired
product 7a, the use of Et2O gave the product in 58% yield
with 54% ee (entries 18 and 19).
O
CH2Cl2, –78 °C
24 h
Ph
H
Ph
5a
6a
7
Entry
Additives
Yield (%)b
ee (%)c
1
2
3
4
5
6
7
8
–
73
81
70
85
72
77
90
93
85
46
70
69
78
48
65
39
t-BuOH
CF3CH2OH
4-MeOC6H4OH
2,6-t-Bu2C6H3OH
4-BrC6H4OH
2,6-t-Bu2-4-MeOC6H2OH
PhCO2H
a Reaction conditions: 5a (0.05 mmol), 6a (0.10 mmol), additives (0.15
mmol, 0.2 M).
b Isolated yield.
c Determined by HPLC analysis using a chiral stationary phase.
To improve the efficiency of the reaction, several addi-
tives were examined. With the assumption that inhibition
of the catalyst might occur as a result of undesired interac-
tion of the boronic acid ester of 7 with catalyst 2, the effect
of protic additives was then studied. Accordingly, both alco-
holic and phenolic additives were found to accelerate the
reaction (Table 2). 2,6-Di-tert-butyl-4-methoxyphenol gave
7a in 90% yield, but a reduction of the enantioselectivity
was observed (entry 7). Given that dicarboxylic acid cata-
lyst 1a showed superior performance in terms of the chem-
ical yield (Table 1, entry 1), carboxylic acid was tested as an
additive. However, the addition of benzoic acid resulted in
drastic loss of the enantioselectivity, although the yield was
high (entry 8).
The substrate generality of the asymmetric allylbora-
tion reaction of aldehydes was then investigated under the
optimum reaction conditions14 identified above in Table 1,
entry 12. Careful monitoring of the model reaction revealed
that a similar chemical yield was obtained after a much
shorter reaction time (Table 3, entry 1). However, the fol-
lowing reactions were run for 24 h, since a longer reaction
time was sometimes necessary because of the low solubili-
ty of the aldehydes. A bulkier 2-naphthylaldehyde (5b) gave
similar levels of yield and enantioselectivity (entry 2). Ha-
logenated aldehydes generally gave the corresponding
products in higher yield. Although moderate enantioselec-
tivity was observed in the case of sterically congested or-
tho-substituted aldehydes 5c and 5d (entries 3 and 4), me-
ta- and para-substituted halogenated substrates underwent
the reaction with high enantioselectivity (entries 5–7). The
reactions of aldehydes having an electron-withdrawing
para-trifluoromethyl or para-cyano group proceeded
smoothly with 85 and 80% ee, respectively (entries 8 and 9),
whereas the reaction of 5j, with an electron-donating para-
methyl group, gave a low enantioselectivity (entry 10). Al-
though the allylboration of heteroaromatic aldehyde 5k and
α,β-unsaturated aldehyde 5l also proceeded nicely at higher
Table 3 The Generality of the Reactiona
O
OH
2d (10 mol%)
O
B
+
CH2Cl2, –78 °C
24 h
O
R
H
Ar
5a
6a
7
Entry
R
Product
Yield (%)b
ee (%)c
1d
2
Ph
5a
5b
5c
5d
5e
5f
7a
7b
7c
7d
7e
7f
74
70
90
92
85
96
66
74
90
90
93
69
65
65
85
75
47
49
84
83
85
85
80
29
43
43
35
66
2-naphthyl
2-ClC6H4
2-BrC6H4
3-ClC6H4
3-BrC6H4
4-BrC6H4
4-F3CC6H4
4-NCC6H4
4-MeC6H4
2-thienyl
3
4
5
6
7
5g
5h
5i
7g
7h
7i
8
9
10
11e
12f
13
14
5j
7j
5k
5l
7k
7l
(E)-PhCH=CH
PhCH2CH2
c-C6H11
5m
5n
7m
7n
a Reaction conditions: 5a (0.10 mmol), 6a (0.20 mmol, 0.2 M).
b Isolated yield.
c Determined by HPLC analysis using a chiral stationary phase.
d 5 h.
e Reaction was run in 1,2-dichloroethane at room temperature (2 h).
f Reaction was run at –35 °C.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

D
Y. Ota et al.
Letter
Synlett
reaction temperature, the enantioselectivity was unsatis-
factory (entries 11 and 12). Aliphatic aldehydes were also
applicable, albeit with moderate enantioselectivity (entries
13 and 14).
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0036-1588690.
S
u
p
p
o
nrtIo
g
f
rmoaitn
S
u
p
p
ortiInfogrmoaitn
We then directed our efforts to applying the catalytic
conditions thus obtained to the enantioselective propar-
gylation of aldehydes to produce synthetically useful ho-
mopropargylic alcohols (Table 4).15 Recently, the utility of
allenyl boronic acid pinacol ester (9) was explored in Brøn-
sted acid catalyzed enantioselective propargylation of alde-
hydes, since 9 is a nontoxic and relatively air- and moisture-
stable reagent.16 Compared with 6a, allenylboronate 9 was
found to be less reactive. Although higher reaction tem-
perature and longer reaction times were required to reach
completion, the reaction of benzaldehyde (5a) and 9 afford-
ed the desired homopropargyl alcohol 10a in 81% yield
with 57% ee (entry 1). This reaction was applicable to other
aldehydes, furnishing the corresponding homopropargylic
alcohol with promising enantioselectivities (entries 2–4).
References and Notes
(1) (a) Schreiner, P. R. Chem. Soc. Rev. 2003, 32, 289. (b) Rueping,
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(3) For recent reviews of chiral phosphoric acid catalysis, see:
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dron 2015, 71, 6384.
Table 4 Asymmetric Allenylboration of Aldehydesa
OH
O
O
B
2d (10 mol%)
+
•
R
R
H
O
CH2Cl2, 0 °C
10
5
6
Entry
R
Product
Yield (%)b
ee (%)c
1
2
3
4
Ph
5a
5f
10a
10f
10h
10i
81
50
92
99
57
65
63
66
3-BrC6H4
4-F3CC6H4
4-NCC6H4
(6) Egami, H.; Asada, J.; Sato, K.; Hashizume, D.; Kawato, Y.;
Hamashima, Y. J. Am. Chem. Soc. 2015, 137, 10132.
5h
5i
(7) For recent reviews on asymmetric allylation reaction, see:
(a) Chemler, S. R.; Roush, W. R. In Modern Carbonyl Chemistry;
Wiley-VCH: Weinheim, 2000, 403–490. (b) Denmark, S. E.; Fu, J.
Chem. Rev. 2003, 103, 2763. (c) Kennedy, J. W. J.; Hall, D. G. In
Boronic Acids: Preparation and Applications in Organic Synthesis
and Medicine; Wiley-VCH: Weinheim, 2005, Chap. 6, 241.
(d) Hall, D. G. Synlett 2007, 1644. (e) Lachance, H.; Hall, D. G.
Org. React. 2008, 73, 1. (f) Yus, M.; González-Gómez, J. C.;
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X.; Duvall, J. R.; Huanga, M.-Y.; Hong, R. Org. Chem. Front. 2014,
1, 303.
(8) For selected examples for metal complex catalyzed allylbora-
tion, see: Cu: (a) Wada, R.; Oisaki, K.; Kanai, M.; Shibasaki, M.
J. Am. Chem. Soc. 2004, 126, 8910. (b) Shi, S.-L.; Xu, L.-W.; Oisaki,
K.; Kanai, M.; Shibasaki, M. J. Am. Chem. Soc. 2010, 132, 6638.
For Zn, see: (c) Kobayashi, S.; Endo, T.; Ueno, M. Angew. Chem.
Int. Ed. 2011, 50, 12262. (d) Cui, Y.; Yamashita, Y.; Kobayashi, S.
Chem. Commun. 2012, 48, 10319. (e) Cui, Y.; Wei, L.; Sato, T.;
Yamashita, Y.; Kobayashi, S. Adv. Synth. Catal. 2013, 355, 1193.
For Ni, see: (f) Zang, P.; Morken, J. P. J. Am. Chem. Soc. 2009, 131,
12550. For In, see: (g) Schneider, U.; Ueno, M.; Kobayashi, S.
J. Am. Chem. Soc. 2008, 130, 13824. For Sn, see: (h) Rauniyar, V.;
Hall, D. G. Angew. Chem. Int. Ed. 2006, 45, 2426. (i) Rauniyar, V.;
Zhai, H.; Hall, D. G. J. Am. Chem. Soc. 2008, 130, 8481. (j) Bhakta,
U.; Sullivan, E.; Hall, D. G. Tetrahedron 2014, 70, 678.
a Reaction conditions: 5a (0.10 mmol), 9 (0.20 mmol), 0.2 M.
b Isolated yield.
c Determined by HPLC analysis using a chiral stationary phase.
In summary, we have developed a chiral hydroxyl car-
boxylic acid catalyzed asymmetric allylboration of alde-
hydes. This methodology provided synthetically useful ho-
moallyl alcohols in high enantioselectivity. The present cat-
alytic protocol was also applicable to the asymmetric
propargylation of aldehydes with allenyl boronic acid pina-
col ester. It is interesting that the co-presence of both the
carboxylic acid and the hydroxyl group at the defined posi-
tion was essential for high asymmetric induction. This
study provides guidance for the design of novel catalysts, al-
lowing the toolbox available for organocatalysis to be ex-
panded. Further improvement of the efficiency of the reac-
tion and elucidation of a more detailed reaction mechanism
are currently underway in our laboratory.
Acknowledgment
This work was supported by JSPS KAKENHI Grant Number 16H05077.
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(9) For reviews of asymmetric organocatalysis, see: (a) Dalko, P. I.;
Moisan, L. Angew. Chem. Int. Ed. 2001, 40, 3726. (b) Dalko, P. I.;
Moisan, L. Angew. Chem. Int. Ed. 2004, 43, 5138. (c) Taylor, M. S.;
Jacobsen, E. N. Angew. Chem. Int. Ed. 2006, 45, 1520.
acid pinacol ester (6a; 37 μL, 0.20 mmol) was added by using a
gas-tight syringe with a stainless steel needle. The reaction
mixture was stirred at the same temperature for 5 h. The reac-
tion was quenched with DIBAL-H (1.0 M in toluene, 15 μL). After
stirring for 10 min, 4 M HCl was added to the mixture and the
aqueous layer was extracted with CH2Cl2. The combined organic
layers were washed with brine and dried over Na2SO4. After
evaporation of the solvent under reduced pressure, the reaction
mixture was purified by flash chromatography (EtOAc/hexanes,
(10) For selected examples of asymmetric allylboration through
ester exchange, see: (a) Lou, S.; Moquist, P. N.; Schaus, S. E.
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Hoveyda, A. H. Nature Chem. 2016, 8, 768. (f) Robbins, D. W.;
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Angew. Chem. Int. Ed. 2016, 55, 9610.
29
1:9) to give 7a (11.0 mg, 74%) as a colorless oil; [α]D –56.3 (c
0.72, CHCl3, 85% ee sample). 1H NMR (CDCl3): δ = 7.37–7.25 (m,
5 H), 5.82 (dddd, J = 17.2, 10.3, 7.5, 6.9 Hz, 1 H), 5.21–5.13 (m,
2 H), 4.75 (t, J = 6.3 Hz, 1 H), 2.57–2.47 (m, 2 H), 2.03 (br s, 1 H).
13C NMR (CDCl3): δ = 143.9, 134.4, 128.4, 127.5, 125.8, 118.4,
73.3, 43.8. CHIRALCEL OD-H (ϕ 0.46 cm × 25 cm; 2-propanol/n-
hexane, 5:95; flow rate 0.5 mL/min, detection at 210 nm; tR
14.5 (R), 16.6 (S) min.
=
(15) For reviews on enantioselective propargylation, see: (a) Marshall,
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Wynn, T. J. Am. Chem. Soc. 2001, 123, 6199. (d) Evans, D. A.;
Sweeney, Z. K.; Rovis, T.; Tedrow, J. S. J. Am. Chem. Soc. 2001,
123, 12095. (e) Hernandez, E.; Burgos, C. H.; Alicea, E.;
Soderquist, J. A. Org. Lett. 2006, 8, 4089. (f) Fandrick, D. R.;
Fandrick, K. R.; Reeves, J. T.; Tan, Z.; Tang, W.; Capacci, A. G.;
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J. Am. Chem. Soc. 2010, 132, 7600. (g) Barnett, D. S.; Schaus, S. E.
Org. Lett. 2011, 13, 4020. (h) Chen, J.; Captain, B.; Takenaka, N.
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J. Angew. Chem. Int. Ed. 2012, 51, 7830. (j) Haddad, T. D.;
Hirayama, L. C.; Buckley, J. J.; Singaram, B. J. Org. Chem. 2012, 77,
889. (k) Hirayama, L. C.; Haddad, T. D.; Oliver, A. G.; Singaram, B.
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Jiménez, S.; Lapuerta, I.; Mielgo, A.; Odriozola, J. M.; Otaza, I.;
Razkin, J.; Urruzuno, I.; Vera, S.; Oiarbide, M.; Palomo, C. Chem.
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(11) For selected examples of asymmetric allylboration through the
activation of allyl boronates by Brønsted acid, see: (a) Jain, P.;
Antilla, J. C. J. Am. Chem. Soc. 2010, 132, 11884. (b) Xing, C.-H.;
Liao, Y.-X.; Zhang, Y.; Sabarova, D.; Bassous, M.; Hu, Q.-S. Eur. J.
Org. Chem. 2012, 1115. (c) Wang, H.; Jain, P.; Antilla, J. C.; Houk,
K. N. J. Org. Chem. 2013, 78, 1208. (d) Incerti-Pradillos, C. A.;
Kabeshov, M. A.; Malkov, A. V. Angew. Chem. Int. Ed. 2013, 52,
5338. (e) Barrio, P.; Rodriguez, E.; Saito, K.; Fustero, S.; Akiyama,
T. Chem. Commun. 2015, 51, 5246. (f) Rodriguez, E.; Grayson, M.
N.; Asensio, A.; Barrio, P.; Houk, K. N.; Fustero, S. ACS Catal.
2016, 6, 2506.
(12) (a) Charville, H.; Jackson, D.; Hodges, G.; Whiting, A. Chem.
Commun. 2010, 46, 1813. (b) Ishihara, K.; Ohara, S.; Yamamoto,
H. J. Org. Chem. 1996, 61, 4196. (c) Azuma, T.; Murata, A.;
Kobayashi, Y.; Inokuma, T.; Takemoto, Y. Org. Lett. 2014, 16,
4256.
(13) Other hydrogen bonding interactions with aldehyde might be
involved in the transition state, see: (a) Grayson, M. N.;
Pellegrinet, S. C.; Goodman, J. M. J. Am. Chem. Soc. 2012, 134,
2716. (b) See also refs. 7h and 11c.
(14) General Procedure: To a flame-dried glass tube equipped with
a three-way top were placed chiral acid catalyst 2d (12.3 mg,
0.010 mmol), freshly distilled benzaldehyde (5a; 10 μL, 0.10
mmol), and anhydrous CH2Cl2 (0.5 mL) under Ar atmosphere.
The resulting solution was cooled at –78 °C before allylboronic
(16) (a) Reddy, L. R. Org. Lett. 2012, 14, 1142. (b) Jain, P.; Wang, H.;
Houk, K. N.; Antilla, J. C. Angew. Chem. Int. Ed. 2012, 51, 1391.
(c) Grayson, M. N.; Goodman, J. M. J. Am. Chem. Soc. 2013, 135,
6142. (d) See also, refs. 11c, 11f.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E