A practical synthesis of morita-baylis-hillman adducts of aryl vinyl ketones catalyzed by a proton donor

Article abstract of DOI:10.5012/bkcs.2012.33.6.2023

An efficient and practical synthesis of MBH adducts of aryl vinyl ketones was developed using DABCO and 4-nitrophenol as a proton donor. Addition of a proton donor and the use of excess amounts (3.0 equiv) of aldehydes were highly beneficial for the yield

Full text of DOI:10.5012/bkcs.2012.33.6.2023

A Practical Synthesis of Morita-Baylis-Hillman Adducts
Bull. Korean Chem. Soc. 2012, Vol. 33, No. 6 2023
http://dx.doi.org/10.5012/bkcs.2012.33.6.2023
A Practical Synthesis of Morita-Baylis-Hillman Adducts of Aryl Vinyl Ketones
Catalyzed by a Proton Donor
*
Sung Hwan Kim, Se Hee Kim, Cheol Hee Lim, and Jae Nyoung Kim
Department of Chemistry and Institute of Basic Science, Chonnam National University, Gwangju 500-757, Korea
*
E-mail: kimjn@chonnam.ac.kr
Received March 15, 2012, Accepted March 24, 2012
An efficient and practical synthesis of MBH adducts of aryl vinyl ketones was developed using DABCO and
4-nitrophenol as a proton donor. Addition of a proton donor and the use of excess amounts (3.0 equiv) of
aldehydes were highly beneficial for the yields of MBH adducts of aryl vinyl ketones.
Key Words : Morita-Baylis-Hillman adducts, Aryl vinyl ketones, Proton donor, 4-Nitrophenol
Introduction
Oh and Li reported a cooperative catalyst system of proline
3c
and brucine N-oxide (equation 3 in Scheme 1). However,
The Morita-Baylis-Hillman (MBH) reaction is one of the
both reactions have some limitations to be used generally in
a practical sense. For the sila-MBH reaction, a-silylated aryl
vinyl ketones and a special catalyst TTMPP (tris(2,4,6-
trimethoxyphenyl)phosphine) were required. For the latter
method, excess amounts of valuable PVK and an equimolar
amount of commercially unavailable brucine N-oxide have
to be used.
1
most powerful methods of carbon-carbon bond-formation.
The reaction was shown to be highly efficient with various
Michael acceptors such as acrylates, acrylonitriles, and alkyl
1
vinyl ketones. However, the MBH reaction to form the
MBH adduct 3 is not efficient with phenyl vinyl ketone
2,3
(PVK) due to its high reactivity. Two major side products
2 and 4 were formed in general, as shown in Scheme 1. The
PVK dimer 2 was formed by the Rauhut-Currier reaction via
a conjugate addition of the zwitterion I to PVK. In addition,
the zwitterion I can react with the MBH adduct 3 and
Results and Discussion
In these contexts, we decided to develop a facile synthetic
method of the MBH adducts of aryl vinyl ketones. At the
outset of our study, we examined the effect of molar ratio
between p-nitrobenzaldehyde (1a) and PVK in THF in the
presence of DABCO (10-30 mol %), as shown in Table 1.
2,3a,c
produced the 1:2 adduct 4.
Previously, Trofimov and Gevorgyan reported the syn-
thesis of MBH adduct of PVK via the sila-MBH reaction
using α-silylated aryl vinyl ketone in the presence of a
3a
phosphine catalyst (equation 2 in Scheme 1). Very recently,
2a
As reported in the previous paper, the 1:2 adduct 4a (R = p-
Scheme 1

2024 Bull. Korean Chem. Soc. 2012, Vol. 33, No. 6
Sung Hwan Kim et al.
a
Table 1. Optimization of the MBH reaction of PVK with 4-nitrobenzaldehyde (1a) and 2-nitrobenzaldehyde (1b)
Entry
1 : PVK
DABCO (Equiv)
Additive (Equiv)
Time (h)
2 (%)
3 (%)
4 (%)
b
b
b
b
b
1
1 : 2
1 : 2
1 : 1
2 : 1
3 : 1
0.1
0.1
0.3
0.3
0.3
no
no
no
no
no
60
16
3a (0)
4a (78)
4a (55)
4a (48)
4a (16)
4a (14)
2
3
4
5
40
20
20
20
15
13
3a (15)
3a (37)
3a (70)
3a (72)
10
< 5
6
7
3 : 1
3 : 1
3 : 1
3 : 1
3 : 1
3 : 1
3 : 1
0.5
0.5
0.5
0.5
0.5
0.5
0.5
phenol (0.3)
20
6
< 5
< 5
< 5
13
3a (68)
3a (88)
3a (72)
3a (53)
3a (86)
3a (82)
3a (77)
4a (17)
4-nitrophenol (0.3)
4a (< 5)
4a (17)
4a (22)
4a (< 5)
4a (< 5)
4a (13)
c
8
PEG-3400
20
20
20
20
20
9
MeOH (5.0)
10
11
12
benzoic acid (0.3)
pivalic acid (0.3)
acetaldoxime (0.3)
< 5
< 5
< 5
13
3 : 1
0.3
no
20
32
3b (23)
4b (43)
14
15
3 : 1
3 : 1
0.5
0.5
4-nitrophenol (0.3)
benzoic acid (0.3)
12
20
9
10
c
3b (68)
3b (71)
4b (8)
4b (< 5)
a
b
Common conditions: THF, rt (1a for entries 1-12 and 1b for entries 13-15). Reported results in Ref. 2a. Arbitray amounts of PEG-3400 were used.
nitrophenyl) was formed as a major product along with
appreciable amount of a PVK dimer 2 when we used
1a:PVK = 1:2 ratio (entries 1-2). When the amount of 1a
increased gradually to 3.0 equiv, the yield of MBH adduct
3a increased also to 72% (entries 3-5). Although the yield
(72%, entry 5) was not high, we think the reaction condition
reaction afforded the MBH adduct 3b in low yield (23%)
along with a PVK dimer 2 (32%) and the corresponding 1:2
2a,3c
adduct 4b (43%),
as shown in entry 13.
We think the yields of MBH adducts could be increased by
reducing the formations of a PVK dimer and 1:2 adduct by
completion of the reaction in a short time. Thus we decided
to examine the effect of a proton donor such as phenol in
order to facilitate the MBH reaction. Such a rate-increasing
3
would be more beneficial than the previous methods. Thus
we carried out the reaction of 2-nitrobenzaldehyde (1b) under
the same reaction conditions (1b:PVK = 3:1); however, the
4
effect of a proton donor has been reported by us and other
a
Table 2. Synthesis of MBH adducts of aryl vinyl ketones
Entry
Time (h)
Product (%)
Entry
Time (h)
Product (%)
1
6
7
6
2
12
8
10
3
8
9
6
4
18
10
6
5
12
11
6
6
18
12
6
a
b
Conditions: aldehyde (1.2 mmol), aryl vinyl ketone (0.4 mmol), 4-nitrophenol (30 mol %), DABCO (50 mol %), THF, rt. Conditions: 4-nitrophenol
c
(50 mol %) and DABCO (100 mol %) were used. Under the typical conditions the yield was 39%. 10.0 equiv of acetaldehyde was used.

A Practical Synthesis of Morita-Baylis-Hillman Adducts
Bull. Korean Chem. Soc. 2012, Vol. 33, No. 6 2025
Scheme 2
5,6
8
groups. Thus, we examined the reaction of 1a in the
presence of a proton donor, and the results are summarized
in the Table 1 (entries 6-12, 14 and 15). As shown, the effect
of phenol (entry 6), PEG-3400 (entry 8), MeOH (entry 9),
and acetaldoxime (entry 12) were negligible. When we used
4-nitrophenol as an additive (entry 7), the yield of 3a increased
to 88%. In addition, the reaction of 2-nitrobenzaldehyde
gave the corresponding MBH adduct 3b in an increased
yield (68%, entry 14). It is interesting to note that the addi-
tion of benzoic acid (entry 10) or pivalic acid (entry 11) also
increased the yield of 3a to some extent (vide infra). The
reaction of 1b in the presence of benzoic acid (entry 15) also
afforded a good yield of 4b (71%).
proton donor in these cases might be a protonated DABCO.
In summary, we disclosed an efficient and practical syn-
thesis of MBH adducts of aryl vinyl ketones using DABCO
and 4-nitrophenol as a proton donor. Addition of a proton
donor and the use of excess amounts (3.0 equiv) of aldehydes
were highly beneficial for the yields of MBH adducts of aryl
vinyl ketones.
Experimental Section
Typical Procedure for the Synthesis of 3a. Aryl vinyl
ketones were prepared before use from 3-chloro-1-aryl-
propan-ones by treatment with KOAc in EtOH (reflux, 3 h)
9
as reported. A solution of 4-nitrobenzaldehyde (1a, 181 mg,
Encouraged by the successful results, we carried out the
MBH reactions of aryl vinyl ketones with various aldehydes
and ninhydrin in the presence of DABCO (0.5 equiv) and 4-
nitrophenol (0.3 equiv), and the results are summarized in
Table 2. The reactions of 3-nitrobenzaldehyde, 4-pyridine-
carbaldehyde, and 3-pyridinecarbaldehyde afforded good
yields of MBH adducts 3c-e (entries 3-5), while the reaction
of 4-chlorobenzaldehyde gave low yield (39%) of 3f. The
yield of 3f increased to 54% by using 50 mol % of 4-nitro-
phenol and 100 mol % of DABCO (entry 6). The reactions
of ninhydrin (entry 7) and acetaldehyde (entry 8) also
produced 3g and 3h in good yields (69-92%). The reactions
with 4-chlorophenyl vinyl ketone (entries 9 and 10), 2,4-
dimethoxyphenyl vinyl ketone (entry 11), and 4-methylphenyl
vinyl ketone (entry 12) afforded the corresponding MBH
adducts 3i-l in good yields (79-91%).
1.2 mmol), PVK (53 mg, 0.4 mmol), DABCO (22 mg, 50
mol %), and 4-nitrophenol (17 mg, 30 mol %) in THF (1.5
mL) was stirred at room temperature for 6 h. After the usual
aqueous extractive workup and column chromatographic
purification process (hexanes/Et2O/CH2Cl2, 25:5:1) compound
3a was obtained as pale yellow oil, 100 mg (88%). Other
MBH adducts 3b-l were synthesized similarly, and the
selected spectroscopic data of 3d-l are as follows. MBH
3c
adducts 3a-c were known compounds, and the spectro-
scopic data were identical with the reported.
Compound 3d: 88%; pale yellow oil; IR (film) 3433,
−1
1
1703, 1674, 1597, 1449, 1410 cm ; H NMR (CDCl3, 300
MHz) δ 4.94 (br s, 1H), 5.78 (s, 1H), 5.85 (s, 1H), 6.15 (d, J
= 0.9 Hz, 1H), 7.37-7.44 (m, 4H), 7.52-7.58 (m, 1H), 7.65-
13
7.68 (m, 2H), 8.47 (dd, J = 4.8 and 1.5 Hz, 2H); C NMR
In the MBH reaction, the reaction could be accelerated
by increasing the amount of enolate I, activation of the
aldehyde, or stabilization of the zwitterion III. As shown in
Scheme 2, a stabilization of the intermediate III with 4-
nitrophenol would facilitate the formation of III as well as
(CDCl3, 75 MHz) δ 72.28, 121.43, 127.55, 128.36, 129.45,
132.90, 136.95, 148.03, 149.49, 151.20, 197.64; ESIMS m/z
+
262 (M +Na). Anal. Calcd for C15H13NO2: C, 75.30; H,
5.48; N, 5.85. Found: C, 75.61; H, 5.54; N, 5.59.
Compound 3e: 75%; colorless oil; IR (film) 3399, 1653,
−1
1
the departure of a DABCO moiety, and this increase the
1596, 1427, 1330 cm ; H NMR (CDCl3, 300 MHz) δ 5.00
(br s, 1H), 5.83 (s, 1H), 5.86 (s, 1H), 6.19 (s, 1H), 7.25 (dd, J
= 8.4 and 4.8 Hz, 1H), 7.41 (t, J = 7.5 Hz, 2H), 7.54 (t, J =
7.5 Hz, 1H), 7.67 (d, J = 7.2 Hz, 2H), 7.79-7.82 (m, 1H),
8.40 (dd, J = 4.8 and 1.2 Hz, 1H), 8.58 (d, J = 1.5 Hz, 1H);
5a,d-f,7
whole MBH reaction rate.
In these contexts, various
5,6
5i-k
proton donors and Lewis acids have been known to
increase the reaction rate by stabilizing the zwitterion III.
Thus, an increase of reaction rate by using 4-nitrophenol is
beneficial for the increase of yield of a MBH adduct. In
addition, a rapid consumption of PVK is also important in
order to prohibit the formation of unwanted 1:2 adduct by
using aldehyde/PVK in a 3:1 molar ratio. As noted above,
the addition of carboxylic acid derivatives (entries 10, 11,
and 15 in Table 1) also increased the reaction rate, and a
13
C NMR (CDCl3, 75 MHz) δ 71.22, 123.47, 126.98, 128.31,
129.43, 132.78, 134.58, 137.02, 137.53, 148.09, 148.44,
+
148.56, 197.54; ESIMS m/z 262 (M +Na). Anal. Calcd for
C15H13NO2: C, 75.30; H, 5.48; N, 5.85. Found: C, 75.38; H,
5.60; N, 5.72.
Compound 3f: 54%; colorless oil; IR (film) 3443, 1651,

2026 Bull. Korean Chem. Soc. 2012, Vol. 33, No. 6
Sung Hwan Kim et al.
−1
1
o
Compound 3l: 91%; white solid, mp 165-166 C; IR
1597, 1447, 1333 cm ; H NMR (CDCl3, 300 MHz) δ 3.65
(d, J = 5.4 Hz, 1H), 5.74 (d, J = 5.4 Hz, 1H), 5.79 (s, 1H),
6.07 (d, J = 0.9 Hz, 1H), 7.28-7.32 (m, 2H), 7.35-7.39 (m,
2H), 7.41-7.44 (m, 2H), 7.51-7.57 (m, 1H), 7.65-7.69 (m,
−1
1
(KBr) 3428, 1749, 1715, 1643, 1605, 1337 cm ; H NMR
(CDCl3, 300 MHz) δ 2.38 (s, 3H), 3.58 (br s, 1H), 6.28 (s,
1H), 6.77 (s, 1H), 7.19-7.22 (m, 2H), 7.55-7.59 (m, 2H),
13
2H); C NMR (CDCl3, 75 MHz) δ 73.31, 126.93, 127.84,
13
7.85-7.91 (m, 2H), 8.02-8.08 (m, 2H); C NMR (CDCl3, 75
128.30, 128.58, 129.49, 132.84, 133.43, 137.00, 139.81,
MHz) δ 21.62, 77.18, 124.29, 129.08, 129.71, 131.32, 133.40,
136.09, 141.16, 143.98, 144.76, 195.67, 197.03; ESIMS m/z
+
+
148.37, 198.08; ESIMS m/z 295 (M +Na), 297 (M +Na+2).
Anal. Calcd for C16H13ClO2: C, 70.46; H, 4.80. Found: C,
70.77; H, 4.93.
+
329 (M +Na). Anal. Calcd for C19H14O4: C, 74.50; H, 4.61.
Found: C, 74.69; H, 4.90.
o
Compound 3g: 92%; white solid, mp 105-106 C; IR
−1
1
(KBr) 3433, 1749, 1715, 1645, 1595, 1337, 1265 cm ; H
NMR (CDCl3, 300 MHz) δ 3.95 (s, 1H), 6.30 (s, 1H), 6.83
(s, 1H), 7.37-7.42 (m, 2H), 7.51-7.57 (m, 1H), 7.63-7.67 (m,
Acknowledgments. This work was supported by the
National Research Foundation of Korea Grant funded by the
Korean Government (2011-0002570). Spectroscopic data
were obtained from the Korea Basic Science Institute,
Gwangju branch.
13
2H), 7.85-7.91 (m, 2H), 8.01-8.07 (m, 2H); C NMR
(CDCl3, 75 MHz) δ 77.09, 124.27, 128.35, 129.45, 132.17,
132.93, 136.09, 141.09, 144.69, 196.07, 197.10 (1 carbon is
+
overlapped); ESIMS m/z 315 (M +Na). Anal. Calcd for
References and Notes
C18H12O4: C, 73.97; H, 4.14. Found: C, 74.14; H, 4.03.
1. For the general review on Morita-Baylis-Hillman reaction, see: (a)
Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem. Rev. 2003,
103, 811-891. (b) Basavaiah, D.; Reddy, B. S.; Badsara, S. S.
Chem. Rev. 2010, 110, 5447-5674. (c) Singh, V.; Batra, S.
Tetrahedron 2008, 64, 4511-4574. (d) Declerck, V.; Martinez, J.;
Lamaty, F. Chem. Rev. 2009, 109, 1-48. (e) Ciganek, E. In
Organic Reactions; Paquette, L. A., Ed.; John Wiley & Sons: New
York, 1997; Vol. 51, pp 201-350. (f) Kim, J. N.; Lee, K. Y. Curr.
Org. Chem. 2002, 6, 627-645. (g) Lee, K. Y.; Gowrisankar, S.;
Kim, J. N. Bull. Korean Chem. Soc. 2005, 26, 1481-1490. (h)
Radha Krishna, P.; Sachwani, R.; Reddy, P. S. Synlett 2008, 2897-
2912. (i) Gowrisankar, S.; Lee, H. S.; Kim, S. H.; Lee, K. Y.; Kim,
J. N. Tetrahedron 2009, 65, 8769-8780. (j) Shi, M.; Wang, F.-J.;
Zhao, M.-X.; Wei, Y. The Chemistry of the Morita-Baylis-Hillman
Reaction; RSC Publishing: Cambridge, UK, 2011.
Compound 3h: 69%; colorless oil; IR (film) 3443, 1649,
−1
1
1595, 1449, 1337, 1292 cm ; H NMR (CDCl3, 300 MHz) δ
1.45 (d, J = 6.6 Hz, 3H), 3.18 (br s, 1H), 4.86 (q, J = 6.6 Hz,
1H), 5.71 (s, 1H), 6.12 (s, 1H), 7.44-7.50 (m, 2H), 7.55-7.61
13
(m, 1H), 7.76-7.80 (m, 2H); C NMR (CDCl3, 75 MHz) δ
21.99, 67.62, 124.93, 128.25, 129.48, 132.64, 137.40,
+
150.36, 198.70; ESIMS m/z 199 (M +Na). Anal. Calcd for
C11H12O2: C, 74.98; H, 6.86. Found: C, 74.69; H, 6.92.
Compound 3i: 86%; pale yellow oil; IR (film) 3474,
−1
1
1651, 1587, 1520, 1346 cm ; H NMR (CDCl3, 300 MHz) δ
3.72 (d, J = 5.7 Hz, 1H), 5.85 (d, J = 5.7 Hz, 1H), 5.86 (s,
1H), 6.13 (d, J = 1.2 Hz, 1H), 7.40 (dt, J = 9.0 and 2.1 Hz,
2H), 7.59-7.65 (m, 4H), 8.19 (dt, J = 9.0 and 2.1 Hz, 2H);
2. For the synthesis of a PVK dimer and 1:2 adduct, see: (a) Shi, M.;
Li, C.-Q.; Jiang, J.-K. Helv. Chim. Acta 2002, 85, 1051-1057. (b)
Basavaiah, D.; Gowriswari, V. V. L.; Bharathi, T. K. Tetrahedron
Lett. 1987, 28, 4591-4592. (c) Idahosa, K. C.; Molefe, D. M.;
Pakade, V. E.; Brown, M. E.; Kaye, P. T. S. Afr. J. Chem. 2011, 64,
144-150.
13
C NMR (CDCl3, 75 MHz) δ 73.10, 123.69, 127.19, 127.86,
128.80, 130.84, 134.98, 139.65, 147.36, 147.58, 148.54,
+
+
196.46; ESIMS m/z 340 (M +Na), 342 (M +Na+2). Anal.
Calcd for C16H12ClNO4: C, 60.48; H, 3.81; N, 4.41. Found:
C, 60.52; H, 3.98; N, 4.29.
3. For the successful synthesis of MBH adducts of PVK, see: (a)
Trofimov, A.; Gevorgyan, V. Org. Lett. 2009, 11, 253-255. (b)
Matsumoto, K.; Oshima, K.; Utimoto, K. Chem. Lett. 1994, 1211-
1214. (c) Oh, K.; Li, J.-Y. Synthesis 2011, 1960-1967. (d) Aranha,
R. M.; Bowser, A. M.; Madalengoitia, J. S. Org. Lett. 2009, 11,
575-578.
o
Compound 3j: 85%; white solid, mp 108-110 C; IR
−1
1
(KBr) 3416, 1703, 1674, 1589, 1406 cm ; H NMR (CDCl3,
300 MHz) δ 5.38 (br s, 1H), 5.80 (s, 1H), 5.81 (s, 1H), 6.16
(s, 1H), 7.36 (d, J = 6.0 Hz, 2H), 7.39 (d, J = 8.4 Hz, 2H),
13
7.61 (d, J = 8.4 Hz, 2H), 8.43 (d, J = 6.0 Hz, 2H); C NMR
4. Kim, K. H.; Lee, H. S.; Kim, Y. M.; Kim, J. N. Bull. Korean
Chem. Soc. 2011, 32, 1087-1090.
(CDCl3, 75 MHz) δ 71.71, 121.50, 127.02, 128.70, 130.80,
135.20, 139.38, 148.18, 149.35, 151.35, 196.11; ESIMS m/z
5. For the rate increase by proton donor additive in DABCO-
catalyzed MBH reactions, see: (a) Maher, D. J.; Connon, S. J.
Tetrahedron Lett. 2004, 45, 1301-1305. (b) Shi, M.; Liu, X.-G.
Org. Lett. 2008, 10, 1043-1046. (c) Amarante, G. W.; Benassi, M.;
Milagre, H. M. S.; Braga, A. A. C.; Maseras, F.; Eberlin, M. N.;
Coelho, F. Chem. Eur. J. 2009, 15, 12460-12469. (d) Aggarwal, V.
K.; Emme, I.; Fulford, S. Y. J. Org. Chem. 2003, 68, 692-700. (e)
Aggarwal, V. K.; Dean, D. K.; Mereu, A.; Williams, R. J. Org.
Chem. 2002, 67, 510-514. (f) Yu, C.; Liu, B.; Hu, L. J. Org. Chem.
2001, 66, 5413-5418. (g) de Souza, R. O. M. A.; Pereira, V. L. P.;
Esteves, P. M.; Vasconcellos, M. L. A. A. Tetrahedron Lett. 2008,
49, 5902-5905. (h) Gruttadauria, M.; Giacalone, F.; Meo, P. L.;
Marculescu, A. M.; Riela, S.; Noto, R. Eur. J. Org. Chem. 2008,
1589-1596. Various Lewis acids have also been used for the same
purpose, see: (i) Aggarwal, V. K.; Mereu, A.; Tarver, G. J.;
McCague, R. J. Org. Chem. 1998, 63, 7183-7189. (j) Yang, K.-S.;
Lee, W.-D.; Pan, J.-F.; Chen, K. J. Org. Chem. 2003, 68, 915-919.
(k) Yukawa, T.; Seelig, B.; Xu, Y.; Morimoto, H.; Matsunaga, S.;
+
+
296 (M +Na), 298 (M +Na+2). Anal. Calcd for C15H12ClNO2:
C, 65.82; H, 4.42; N, 5.12. Found: C, 65.84; H, 4.67; N,
5.01.
Compound 3k: 79%; colorless oil; IR (film) 3439, 1645,
−1
1
1605, 1520, 1346 cm ; H NMR (CDCl3, 300 MHz) δ 3.73
(s, 3H), 3.83 (s, 3H), 4.04 (d, J = 6.3 Hz, 1H), 5.78 (d, J =
6.3 Hz, 1H), 5.79 (s, 1H), 6.00 (d, J = 0.6 Hz, 1H), 6.43 (d, J
= 2.1 Hz, 1H), 6.47 (dd, J = 8.7 and 2.1 Hz, 1H), 7.24 (d, J =
13
C
8.7 Hz, 1H), 7.60-7.65 (m, 2H), 8.15-8.20 (m, 2H);
NMR (CDCl3, 75 MHz) δ 55.44 (2C), 73.15, 98.68, 104.49,
120.28, 123.33, 127.27, 127.76, 132.16, 147.07, 149.28,
159.59, 163.77, 197.26 (1 carbon is overlapped); ESIMS m/z
+
366 (M +Na). Anal. Calcd for C18H17NO6: C, 62.97; H,
4.99; N, 4.08. Found: C, 63.20; H, 5.17; N, 4.03.

A Practical Synthesis of Morita-Baylis-Hillman Adducts
Bull. Korean Chem. Soc. 2012, Vol. 33, No. 6 2027
4723-4725.
Berkessel, A.; Shibasaki, M. J. Am. Chem. Soc. 2010, 132, 11988-
11992.
7. For a detailed MBH reaction mechanism, see: (a) Robiette, R.;
Aggarwal, V. K.; Harvey, J. N. J. Am. Chem. Soc. 2007, 129,
15513-15525 and further references cited therein. (b) Aggarwal,
V. K.; Fulford, S. Y.; Lloyd-Jones, G. C. Angew. Chem. Int. Ed.
2005, 44, 1706-1708. (c) Price, K. E.; Broadwater, S. J.; Walker,
B. J.; McQuade, D. T. J. Org. Chem. 2005, 70, 3980-3987. (d)
Price, K. E.; Broadwater, S. J.; Jung, H. M.; McQuade, D. T. Org.
Lett. 2005, 7, 147-150.
6. For the rate increase by proton donor additive in phosphine or
other Lewis base-catalyzed MBH reactions, see: (a) Shi, M.; Liu,
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