Substrate-controlled regioselective cobalt(I)-catalysed 1,4-hydrovinylation reactions

Article abstract of DOI:10.1055/s-0030-1258408

The substrate-directed regiochemistry of the cobalt-catalysed 1,4-hydrovinylation reaction is described. A variety of symmetrical and unsymmetrical 2,3-disubstituted 1,3-dienes are synthesised by ruthenium-catalysed enyne metathesis, and then reacted with a terminal alkene catalysed by cobalt(II) bromide-[1,2-bis(diphenylphosphino)ethane] [CoBr ²(dppe)] under reductive conditions. The regiochemistry of the branched 1,4-diene products is influenced by the nature of the substituents on the unsymmetrical 2,3-disubstituted 1,3-dienes. The influence of steric and electronic effects is also discussed. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0030-1258408

662
PAPER
Substrate-Controlled Regioselective Cobalt(I)-Catalysed 1,4-Hydrovinylation
Reactions
S
ubstrate-Controll
e
edHydrovi
r
nylationhard Hilt,* Stefan Roesner
Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg, Germany
Fax +49(6421)2825677; E-mail: Hilt@chemie.uni-marburg.de
Received 23 November 2010
When unsymmetrical 1,3-dienes were used as starting ma-
Abstract: The substrate-directed regiochemistry of the cobalt-
catalysed 1,4-hydrovinylation reaction is described. A variety of
symmetrical and unsymmetrical 2,3-disubstituted 1,3-dienes are
synthesised by ruthenium-catalysed enyne metathesis, and then re-
terials in the cobalt-catalysed 1,4-hydrovinylation reac-
tion, a mixture of two different regioisomers (e.g. 3 and 4)
was obtained (Scheme 2). The regiochemical outcome of
acted with a terminal alkene catalysed by cobalt(II) bromide–[1,2- the reaction is determined in the ligand sphere of the co-
bis(diphenylphosphino)ethane] [CoBr2(dppe)] under reductive con-
balt centre during formation of the carbon–carbon bond.
ditions. The regiochemistry of the branched 1,4-diene products is
The regiochemistry might therefore be influenced by ei-
influenced by the nature of the substituents on the unsymmetrical
ther the steric or electronic effects of the 1,3-diene. In this
2,3-disubstituted 1,3-dienes. The influence of steric and electronic
study the influence of a variety of substituents bound to an
effects is also discussed.
unsymmetrical 2,3-disubstituted 1,3-diene was investigat-
ed in order to control the regiochemistry of the cobalt-
Key words: alkene, catalysis, cobalt, diene, regioselectivity
catalysed 1,4-hydrovinylation reaction.
Among atom economic cobalt-catalysed carbon–carbon
bond-forming processes,1 the cobalt-catalysed 1,4-hy-
drovinylation reaction of symmetrical 1,3-dienes with a
terminal alkene is a convenient method for the synthesis
of 1,4-dienes such as 1, under mild reaction conditions.2
This efficient and atom economic reaction utilising a co-
balt catalyst system [abbreviated as Co(I)] makes use of a
mixture of cobalt(II) bromide–[1,2-bis(diphenylphosphi-
no)ethane] [CoBr2(dppe)], zinc iodide (ZnI2) and zinc
powder in dichloromethane at ambient temperature. This
catalyst system tolerates a variety of functional groups
leading to functionalised 1,4-dienes. These dienes are of
significant synthetic value and products such as 1,3-dicar-
bonyl compounds 2 are easily accessible via ozonolysis
(Scheme 1). In this context, the 1,4-hydrovinylation reac-
tion has been used as the key step in the synthesis of small
natural products containing a 1,4-diene subunit as in 1, or
a 1,3-dicarbonyl moiety as found in 2.3
R1
Co(I)
+
or
or
R1
R2
R1
R2
R2
3
4
O3, Me2S
O3, Me2S
O
O
O
H
O
R1
R2
R2
5
6
Scheme 2 Cobalt-catalysed 1,4-hydrovinylation of 2-substituted
1,3-butadienes with terminal alkenes followed by ozonolysis for the
synthesis of 1,3-dicarbonyl compounds
The motivation behind this study was the need to develop
a regioselective cobalt-catalysed 1,4-hydrovinylation re-
action for the synthesis of 1,3-dicarbonyl compounds util-
ising a regiodirecting substituent on the 1,3-diene.
Thereby, ‘valuable’ substituents (R1) would remain in the
carbon chain, attached to R2, as in compound 5, after ozo-
nolysis. The cobalt-catalysed 1,4-hydrovinylation leading
to 4 would result in undesired scission of the R1 and R2
substituents after ozonolysis. Previous investigations con-
cerning the regioselective cobalt-catalysed 1,4-hydrovi-
nylation reactions of non-activated terminal alkenes
showed that, unfortunately, products of type 4 were
formed predominantly.2a–f
Co(I)
+
R
R
1
O3, Me2S
O
O
R
2
In order to evaluate the usefulness of the cobalt-catalysed
1,4-hydrovinylation reaction for the transformation of
symmetrical 2,3-disubstituted 1,3-dienes, a small series of
such 1,3-dienes 7 was synthesised utilising a ruthenium-
catalysed enyne metathesis reaction starting from an inter-
nal symmetrical alkyne and ethene (Scheme 3).4 The 1,3-
dienes of type 7 were then converted, over 18 hours em-
ploying two representative terminal alkenes, 1-hexene (8)
Scheme 1 Synthesis of 1,3-dicarbonyl compounds via cobalt-cata-
lysed 1,4-hydrovinylation of 2,3-dimethyl-1,3-butadiene with termi-
nal alkenes followed by ozonolysis
SYNTHESIS 2011, No. 4, pp 0662–0668
x
x
.
x
x
.2
0
1
1
Advanced online publication: 18.01.2011
DOI: 10.1055/s-0030-1258408; Art ID: Z29110SS
© Georg Thieme Verlag Stuttgart · New York

PAPER
Substrate-Controlled Hydrovinylation
663
R
yield, while allyl phthalimide proved to be unreactive in
this transformation. Accordingly, we envisaged that 2,3-
disubstituted 1,3-dienes were suitable starting materials as
long as the substituents were of moderate bulkiness. For
coordination of the 1,3-diene to the cobalt centre, a cisoid
conformation must be adopted; bulky substituents seem to
inhibit effective incorporation of the 1,3-diene during the
transformation.
R
R
Grubbs II
+
O
R
7
N
Bu
8
O
9
Co(I)
Co(I)
O
R
R
R
N
In the next step of the investigation, unsymmetrical 2,3-
disubstituted 1,3-dienes (12, R1 ≠ R2) were generated via
the ruthenium-catalysed enyne metathesis reaction from
unsymmetrical internal alkynes (Scheme 4). When such
1,3-dienes were submitted to the cobalt-catalysed 1,4-hy-
drovinylation reaction utilising allyl phthalimide (9) as
Bu
R
10
11
O
Scheme 3 The ruthenium-catalysed enyne metathesis and cobalt-
catalysed 1,4-hydrovinylation reaction sequence
and allyl phthalimide (9), under cobalt catalysis, into the the terminal alkene the two regioisomeric 1,4-dienes 13
desired products of type 10 and 11.
and 14 were formed. In order to investigate the electronic/
coordinative or steric influence of substituent R2 on the re-
gioselectivity of the 1,4-hydrovinylation reaction, we
designated the substituent R1 to be ‘valuable’, and kept
this substituent as simple as possible for the time being.
Therefore, an n-butyl group was selected which neatly ac-
commodates the need for a dependable and simple route
to unsymmetrical internal alkynes.
The results of the ruthenium-catalysed enyne metathesis–
cobalt-catalysed 1,4-hydrovinylation reaction sequence
are summarised in Table 1.
Table 1 Results of the Ruthenium-Catalysed Enyne Metathesis–
Cobalt-Catalysed Hydrovinylation Reaction of Symmetrical 2,3-Di-
substituted 1,3-Dienes
Entry 1,3-Diene (7)
Product (10/11)a
Yield
(%)b
R2
R2
Grubbs II
+
R1
1
93
86
R1
NPhth
12
11a
9
Co(I)
2
R1
R2
R2
R1
NPhth
O
O
+
11b
Ph
N
N
Ph
13
14
O
O
3
0
NPhth
Ph
11c
Ph
Scheme 4 Substrate-controlled regioselectivity of the cobalt-
catalysed 1,4-hydrovinylation reaction with allyl phthalimide as the
terminal alkene
Ph
Ph
4
0
Ph
The results of preliminary investigations directed towards
a substrate-controlled regioselective cobalt-catalysed 1,4-
hydrovinylation reaction are summarised in Table 2.
Ph
10a
MeO
MeO
5
91c
MeO
When the R2 substituent in unsymmetrical 1,3-diene 12
was a methyl group, two regioisomers, 13 and 14 were ob-
tained as a 1:1 mixture (Table 2, entry 1). Increasing the
steric bulk of substituent R2 to an isopropyl group resulted
in a drastically reduced reactivity such that none of the de-
sired product 14b was obtained. On the other hand, intro-
duction of an isobutyl substituent (Table 2, entry 3)
resulted in the predominant formation of 14c in the ratio
34:66. In this case, the isobutyl substituent favoured the
formation of the desired isomer of type 14. The best result
was obtained when a dimethylphenylsilyl substituent was
used (Table 2, entry 5). In this case, the yield of the two
isomers (36%) and the regioselectivity, in favour of the
preferred regioisomer (13/14 = 29:71), were enhanced.
While the methoxymethyl substituent (Table 2, entry 6)
gave an acceptable yield of 58%, the desired regioisomer
MeO
10b
a NPhth = phthalimide.
b Overall yield of isolated product.
c Reaction time = 61 hours.
Aliphatic, unhindered 1,3-dienes were transformed into
the 1,4-dienes 11a and 11b in excellent yields (Table 1,
entries 1 and 2). In contrast, the more hindered 2,3-diphe-
nyl-1,3-butadiene did not undergo the 1,4-hydrovinyla-
tion reaction with either allyl phthalimide (Table 1, entry
3) or with 1-hexene (Table 1, entry 4). For unknown rea-
sons, 2,3-bis(methoxymethyl)-1,3-butadiene (Table 1,
entry 5) reacted readily with the terminal alkene, 1-hex-
ene, to generate the desired 1,4-diene 10b in very good
Synthesis 2011, No. 4, 662–668 © Thieme Stuttgart · New York

664
G. Hilt, S. Roesner
PAPER
R2
R1
Table 2 Results of the Ruthenium-Catalysed Enyne Metathesis–
Cobalt-Catalysed Hydrovinylation Reaction of Unsymmetrical 2,3-
Disubstituted 1,3-Dienes
R2
R1
Grubbs II
+
15
Co(I)
Entry 1,3-Diene (12)
Product (14)a
Yield
(%)b
8
19
(50:50)
R2
R1
R1
R2
1
NPhth
NPhth
+
14a
14b
n-Bu
n-Bu
16
17
2
3
0
Scheme 5 Substrate-controlled regioselectivity of the cobalt-catalysed
1,4-hydrovinylation reaction with 1-hexene as the terminal alkene
Table 3 Results of the Ruthenium-Catalysed Enyne Metathesis–
Cobalt-Catalysed Hydrovinylation Reaction of Unsymmetrical 2,3-
Disubstituted 1,3-Dienes
28
(34:66)
NPhth
NPhth
NPhth
NPhth
Entry 1,3-Diene (15)
Product (17)
Yield
(%)a
14c
SiMe3
SiMe3
26
(34:66)
4
1
0
14d
n-Bu
SiMe2Ph
17a
SiMe2Ph
36
(29:71)
5
56
(38:62)
2
14e
n-Bu
n-Bu
OMe
OMe
17b
58
(75:25)
6
Ph
Ph
17
(40:60)
3
14f
17c
a NPhth = phthalimide.
Me3Si
b Overall yield of combined isolated product. Ratio of 13/14 in paren-
Me3Si
4
0
theses.
n-Bu
n-Bu
n-Bu
17d
14f was formed as the minor component of the mixture.
The donor atom of the methoxymethyl substituent might
plausibly have altered the regioselectivity of the cobalt-
catalysed reaction, most likely by coordination of the
donor substituent to the cobalt centre so that isomer 13
was formed predominantly. In contrast, steric hindrance
seemed to be responsible for the formation of isomers of
type 14. Based on these results, cobalt-catalysed 1,4-hy-
drovinylation reactions of unsymmetrical 1,3-dienes with
the more reactive 1-hexene (8) were conducted
(Scheme 5).
Et3Si
40
(40:60)
Et3Si
5
17e
MeO
86
(75:25)
MeO
6
17f
MeO
O
20
(72:28)
MeO
O
7
8
n-Bu
17g
The results of these investigations are summarised in
Table 3.
Br MeO
82
(72:28)
Br MeO
n-Bu
Similar to the hydroformylations of allyl phthalimide with
bulky dienes, reactions of hindered 1,3-dienes with 1-hex-
ene gave poor (Table 3, entry 3), or no conversion at all
(Table 3, entries 1 and 4). The isobutyl substituted 1,3-di-
ene was hydroformylated in a reasonably good 56% yield
(Table 3, entry 3). However, the regioselectivities of the
reactions with 1-hexene were somewhat lower compared
to those with allyl phthalimide indicating a slight regio-
17h
a Overall yield of combined isolated product. Ratio of 16/17 in paren-
theses.
directing effect of the substituent bonded to the terminal
alkene. With triethylsilane as substituent R2 (Table 3, en-
try 5), a higher yield, but lower regioselectivity, was ob-
Synthesis 2011, No. 4, 662–668 © Thieme Stuttgart · New York

PAPER
Substrate-Controlled Hydrovinylation
665
served compared to the conversion with allyl phthalimide The results in Table 4 illustrate that the desired products
(Table 2, entry 4). The methoxymethyl substituent gave could be obtained. Nevertheless, the yields were only
the best result in terms of yield and regioselectivity moderate and the regioisomeric ratios were only margin-
(Table 3, entries 6 and 8), although the undesired regio- ally altered by this process, indicating that both isomers
isomers 16f and 16h were formed predominantly in both were reactive to a similar extent.
these cases. An additional donor moiety, as present in the
In conclusion, we have shown that control of the regiose-
methoxymethyl (MOM) group (Table 3, entry 7), led to a
lectivity of the cobalt-catalysed 1,4-hydrovinylation reac-
considerable decrease in yield and no improvement in the
tion can be achieved with bulky substituents in order to
form the desired regioisomers of type 14 and 17. While
the presence of bulky substituents led to some extent of
regioselectivity. The presence of bulky R2 substituents led
mainly to the formation of the desired isomers of type 17,
however, the levels of regiocontrol could not be improved
control of the regioselectivity, the steric hindrance often
using the investigated modifications.
resulted in moderate yields. In contrast, the methoxyme-
In order to prove that some of the 1,4-dienes of types 13/ thyl substituent inverts the regioselectivity of the 1,4-hy-
14 and 16/17 could be converted into the corresponding drovinylation reaction such that products of type 13 and
1,3-dicarbonyl derivatives, ozonolysis with reductive 16 are formed predominantly. Ozonolysis of representa-
workup was performed (Scheme 6). The products were tive 1,4-dienes followed by protection of the resulting un-
isolated and characterised following transformation into symmetrical 1,3-dicarbonyl derivatives using boron
the corresponding dioxoborinine derivatives 18 and 19 us- trifluoride–diethyl ether complex gave dioxoborinines
ing boron trifluoride–diethyl ether complex.
19a,b and 18c. Further improvement in the regioselectiv-
ities may be achieved by altering the ligand in the cobalt
catalyst system. In combination with bulky substituents
located the appropriate distance from the 1,3-diene, good
control of the regioselectivity might be realised in the fu-
ture.
R2
R1
R1
R2
+
R3
R3
1. O3, then Me2S
2. BF3⋅OEt2
F
F
F
F
Column chromatography was performed using silica gel
(Macherey-Nagel, 230–400 mesh) and TLC was carried out using
silica gel plates (Merck). IR spectra were obtained using a Bruker
Physics IFS 200 Interferometer or a Nicolet Magna IR 750 spectro-
photometer. 1H NMR (300 MHz) and 13C NMR (75 MHz) spectra
were recorded using a Bruker Physics AVANCE-300 instrument
with CDCl3 as the solvent. 19F NMR (376 MHz) and 11B NMR (128
MHz) spectra were recorded using a Bruker Physics DRX-400 in-
strument. Low-resolution mass spectra were recorded using a
Varian MAT CH 7A or a Micromass VG 7070 spectrometer for EI
measurements or a Micromass VG Autospec spectrometer for ESI
measurements. HRMS were obtained using a Finnigan MAT 95S
instrument for EI measurements or a Micromass VG Autospec
spectrometer for ESI measurements.
B
B
O
O
O
O
+
R1
R3
R2
R3
18
19
Scheme 6 Ozonolysis of representative 1,4-dienes followed by di-
oxoborinine formation
Table 4 Results of the Ozonolysis–Dioxoborinine Formation Reac-
tion Sequence
Entry 1,4-Diene Product (18/19)a
Yield (%)b
F
F
B
38
(66:34)
O
O
Hydrovinylation; General Procedure
1
2
13c/14c
13e/14e
A Schlenk flask was charged with CoBr2(dppe) (31 mg, 50 mmol,
10 mol%), anhyd ZnI2 (32 mg, 0.1 mmol, 20 mol%) and Zn powder
(7 mg, 0.1 mmol, 20 mol%) under an N2 atm. Next, a soln of the 1,3-
diene (0.5 mmol) in anhyd CH2Cl2 (1.0 mL) and alkene 8 or 9 (0.5–
1.0 mmol) were added. The mixture was stirred at r.t. and the con-
version was monitored by GC–MS. After the conversion was com-
plete, the mixture was diluted with pentane to precipitate the metal
salts and filtered through a small plug of silica gel using Et2O–pen-
tane or EtOAc–pentane as eluent. The solvent was removed and the
residue was purified by column chromatography.
NPhth
NPhth
19a
19a
F
F
B
34
(71:29)
O
O
F
F
B
F
36
(79:21)
O
O
3
4
16e/17e
16f/17f
(4E)-2-(5-Methyl-2-methylene-4-propyloct-4-enyl)isoindoline-
1,3-dione (11a)
Eluent: pentane–Et2O, 5:1; white solid; yield: 1.51 g (4.63 mmol,
19b
F
93%); Rf = 0.38 (pentane–Et2O, 5:1).
B
19
(40:60)
O
O
IR (KBr): 2954, 2924, 2866, 1774, 1713, 1426, 1394, 1107, 949,
907, 725, 711 cm–1.
MeO
1H NMR (300 MHz, CDCl3): d = 7.88–7.83 (m, 2 H), 7.75–7.70 (m,
2 H), 4.82 (d, J = 1.0 Hz, 1 H), 4.76 (d, J = 1.0 Hz, 1 H), 4.20 (s, 2
H), 2.80 (s, 2 H), 2.06–1.94 (m, 4 H), 1.59 (s, 3 H), 1.46–1.26 (m, 4
H), 0.89 (t, J = 7.3 Hz, 3 H), 0.86 (t, J = 7.3 Hz, 3 H).
18c
a NPhth = phthalimide.
b Overall yield of combined isolated product. Ratio of 19/18 in paren-
theses.
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666
G. Hilt, S. Roesner
PAPER
13C NMR (75 MHz, CDCl3): d = 168.1, 141.4, 134.0, 132.1, 132.0,
129.2, 123.3, 110.4, 42.3, 36.8, 36.3, 34.1, 22.1, 21.7, 18.3, 14.3,
14.2.
MS (ESI): m/z (%) = 334 (24) [M + Na]+, 334 (24), 319 (14), 305
(11), 275 (11), 261 (6), 231 (5), 217 (2), 178 (4), 163 (2), 104 (2).
HRMS (ESI): m/z [M + Na]+ calcd for C20H25NO2Na: 334.1778;
found: 334.1779.
MS (EI, 70 eV): m/z (%) = 325 (17) [M]+, 178 (22), 165 (100), 160
(57), 149 (48), 135 (59), 123 (24), 107 (51).
(4E)-2-(4-Butyl-5,7-dimethyl-2-methyleneoct-4-enyl)isoindo-
line-1,3-dione (14c) and (4E)-2-(4-Isobutyl-5-methyl-2-methyl-
enenon-4-enyl)isoindoline-1,3-dione (13c)
HRMS (EI): m/z [M]+ calcd for C21H27NO2: 325.2042;
found: 325.2048.
Eluent: pentane–Et2O, 5:1; yellow solid; combined yield: 50 mg
(0.14 mmol, 28%); ratio (14c/13c) = 66:34; Rf = 0.42 (pentane–
Et2O, 5:1).
(4E)-2-(4-Butyl-5-methyl-2-methylenenon-4-enyl)isoindoline-
1,3-dione (11b)
Eluent: pentane–Et2O, 5:1; white solid; yield: 305 mg (0.86 mmol,
86%); Rf = 0.52 (pentane–Et2O, 5:1).
IR (KBr): 2956, 2866, 1774, 1717, 1462, 1388, 1331, 1104, 955,
721 cm–1.
IR (KBr): 2957, 2926, 2858, 1773, 1718, 1427, 1391, 1106, 963,
942, 725, 712 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.90–7.83 (m, 2 H), 7.75–7.69 (m,
2 H), 4.81 (d, J = 0.9 Hz, 1 H), 4.77 (d, J = 0.9 Hz, 1 H), 4.20 (s, 2
H), 2.79 (s, 2 H), 2.06–1.94 (m, 4 H), 1.59 (s, 3 H), 1.37–1.23 (m, 8
H), 0.94–0.82 (m, 6 H).
13C NMR (75 MHz, CDCl3): d = 168.0, 141.4, 133.9, 132.1, 132.0,
129.1, 123.3, 110.5, 42.3, 36.8, 34.0, 31.6, 31.2, 30.7, 23.0, 22.9,
18.3, 14.1, 14.0.
MS (EI, 70 eV): m/z (%) = 353 (23) [M]+, 206 (16), 193 (100), 163
(30), 160 (46), 149 (41), 121 (10), 107 (25).
HRMS (EI): m/z [M]+ calcd for C23H31NO2: 353.2355;
found: 353.2353.
1H NMR (300 MHz, CDCl3): d = 7.89–7.81 (m, 2 H), 7.75–7.68 (m,
2 H), 4.84 (d, J = 1.0 Hz, 1 H), 4.76 (s, 1 H), 4.21 (s, 2 H), 2.81 (s,
2 H), 2.07–1.72 (m, 5 H), 1.58 (s, 3 H), 1.36–1.19 (m, 4 H), 0.91–
0.80 (m, 9 H). Additional signals of the minor isomer 13c: d = 4.80
(d, J = 1.0 Hz, 1 H), 4.19 (s, 2 H), 2.80 (s, 2 H), 1.60 (s, 3 H).
13C NMR (75 MHz, CDCl3): d = 168.0, 141.5, 134.2, 133.9, 132.1,
130.9, 123.3, 110.5, 43.2, 42.3, 36.8, 31.8, 31.0, 27.1, 23.0, 22.6,
18.5, 14.0. Additional signals of the minor isomer 13c: d = 141.3,
133.1, 128.1, 110.4, 42.3, 40.5, 34.1, 30.7, 27.6, 22.9, 18.4, 14.1.
MS (EI, 70 eV): m/z (%) = 353 (3) [M]+, 193 (17), 187 (100), 169
(39), 160 (26), 158 (11), 130 (24), 104 (32).
HRMS (EI): m/z [M]+ calcd for C23H31NO2: 353.2355;
found: 353.2359.
(2Z)-1-Methoxy-3-(methoxymethyl)-2-methyl-5-methylenenon-
2-ene (10b)
Eluent: pentane–Et2O, 2:1; brown oil; yield: 206 mg (0.91 mmol,
(4E)-2-{2-Methylene-4-[1-(trimethylsilyl)propan-2-ylidene]oc-
tyl}isoindoline-1,3-dione (14d) and (4Z)-2-{5-Methyl-2-methyl-
ene-4-[(trimethylsilyl)methyl]non-4-enyl}isoindoline-1,3-dione
(13d)
Eluent: pentane–Et2O, 5:1; yellow oil; combined yield: 63 mg (0.16
mmol, 26%); ratio (14d/13d) = 66:34; Rf = 0.45 (pentane–Et2O,
5:1).
91%); Rf = 0.66 (pentane–Et2O, 2:1).
IR (neat): 2929, 2873, 1726, 1643, 1457, 1383, 1189, 1093, 892
cm–1.
1H NMR (300 MHz, CDCl3): d = 4.75 (s, 1 H), 4.64 (d, J = 1.6 Hz,
1 H), 4.02 (s, 2 H), 3.89 (s, 2 H), 3.30 (s, 3 H), 3.28 (s, 3 H), 2.87 (s,
2 H), 2.00 (t, J = 7.5 Hz, 2 H), 1.75 (s, 3 H), 1.50–1.22 (m, 4 H),
0.91 (t, J = 7.2 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 146.8, 133.9, 132.5, 109.4, 72.3,
70.5, 57.9, 57.6, 37.3, 36.2, 30.0, 22.4, 16.5, 13.9.
MS (EI, 70 eV): m/z (%) = 226 (<1) [M]+, 194 (15), 179 (10), 162
(14), 137 (100), 123 (23), 119 (68), 105 (33).
IR (KBr): 2955, 2928, 2871, 1774, 1719, 1424, 1391, 1248, 1110,
960, 849, 715 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.89–7.82 (m, 2 H), 7.75–7.69 (m,
2 H), 4.84 (d, J = 1.2 Hz, 1 H), 4.75 (d, J = 1.1 Hz, 1 H), 4.20 (s, 2
H), 2.81 (s, 2 H), 2.00–1.88 (m, 2 H), 1.63–1.51 (m, 5 H), 1.34–1.22
(m, 4 H), 0.92–0.83 (m, 3 H), 0.03 (s, 9 H). Additional signals of the
minor isomer 13d: d = 4.77 (d, J = 1.2 Hz, 1 H), 4.18 (s, 2 H), 2.74
(s, 2 H), –0.03 (s, 9 H).
13C NMR (75 MHz, CDCl3): d = 168.0, 141.8, 133.9, 132.1, 129.1,
126.3, 123.3, 110.2, 42.3, 36.6, 32.1, 30.5, 25.4, 23.0, 21.2, 14.0,
–0.4. Additional signals of the minor isomer 13d: d = 141.2, 128.7,
126.0, 110.5, 42.2, 39.0, 34.6, 30.2, 22.9, 22.3, 17.9, 14.1, –0.6.
MS (EI, 70 eV): m/z (%) = 383 (17) [M]+, 368 (4), 232 (5), 223 (11),
187 (12), 179 (16), 160 (18), 149 (5), 121 (16).
HRMS (EI): m/z [M]+ calcd for C23H33NO2Si: 383.2281;
found: 383.2278.
HRMS (ESI): m/z [M + Na]+ calcd for C14H26O2Na: 249.1825;
found: 249.1811.
2-[2-Methylene-4-(propan-2-ylidene)octyl]isoindoline-1,3-di-
one (14a) and (4E)-2-(4,5-Dimethyl-2-methylenenon-4-
enyl)isoindoline-1,3-dione (13a)
Eluent: pentane–EtOAc, 5:1; white solid; combined yield: 29 mg
(94 mmol, 19%); ratio (14a/13a) = 50:50; Rf = 0.61 (pentane–
EtOAc, 5:1).
Analytical data of the mixture of regioisomers.
(4E)-2-(4-{1-[Dimethyl(phenyl)silyl]propan-2-ylidene}-2-meth-
yleneoctyl)isoindoline-1,3-dione (14e) and (4Z)-2-(4-{[Dimeth-
yl(phenyl)silyl]methyl}-5-methyl-2-methylenenon-4-
enyl)isoindoline-1,3-dione (13e)
Eluent: pentane–Et2O, 5:1; yellow oil; combined yield: 80 mg (0.18
mmol, 36%); ratio (14e/13e) = 71:29; Rf = 0.35 (pentane–Et2O,
5:1).
IR (KBr): 2956, 2927, 2860, 1774, 1718, 1425, 1391, 1329, 1108,
965, 715 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.90–7.81 (m, 4 H), 7.76–7.69 (m,
4 H), 4.84–4.80 (m, 2 H), 4.76 (s, 2 H), 4.19 (s, 4 H), 2.82 (s, 4 H),
2.07–1.95 (m, 4 H), 1.68 (s, 3 H), 1.62 (s, 9 H), 1.35–1.22 (m, 8 H),
0.92–0.83 (m, 6 H).
13C NMR (75 MHz, CDCl3): d = 168.0, 141.5, 141.3, 133.9, 132.1,
131.7, 129.0, 127.3, 124.3, 123.3, 110.7, 110.5, 42.3, 42.0, 39.4,
37.0, 34.4, 31.9, 30.8, 30.4, 22.9, 22.8, 20.7, 20.3, 18.4, 17.9, 14.1,
14.0.
IR (KBr): 2956, 1774, 1718, 1465, 1390, 1110, 956, 834, 715 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.91–7.84 (m, 2 H), 7.75–7.70 (m,
2 H), 7.58–7.44 (m, 2 H), 7.38–7.27 (m, 3 H), 4.83–4.72 (m, 2 H),
4.18 (s, 2 H), 2.81 (s, 2 H), 1.90 (t, J = 7.0 Hz, 2 H), 1.83 (s, 2 H),
Synthesis 2011, No. 4, 662–668 © Thieme Stuttgart · New York

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Substrate-Controlled Hydrovinylation
667
1.55 (s, 3 H), 1.31–1.19 (m, 4 H), 0.91–0.81 (m, 3 H), 0.34 (s, 6 H).
Additional signals of the minor isomer 13e: d = 4.12 (s, 2 H), 2.63
(s, 2 H), 1.76 (s, 2 H), 1.60 (s, 3 H), 0.27 (s, 6 H).
HRMS (EI): m/z [M]+ calcd for C21H42Si: 322.3056;
found: 322.3065.
(5Z)-6-(Methoxymethyl)-5-methyl-8-methylenedodec-5-ene
(16f) and (5E)-5-(1-Methoxypropan-2-ylidene)-7-methylene-
undecane (17f)
Eluent: pentane–EtOAc, 1:1; brown oil; combined yield: 103 mg
(0.43 mmol, 86%); ratio (16f/17f) = 75:25.
13C NMR (75 MHz, CDCl3): d = 168.0, 141.6, 141.1, 133.9, 133.5,
132.1, 128.8, 128.4, 127.7, 127.1, 123.2, 110.3, 42.2, 36.6, 32.1,
30.3, 24.7, 23.0, 21.2, 13.9, –2.1. Additional signals of the minor
isomer 13e: d = 141.1, 139.6, 129.5, 128.7, 127.6, 125.3, 123.3,
110.4, 42.0, 38.7, 34.6, 30.1, 22.9, 21.6, 17.9, 14.0, –2.3.
IR (neat): 2958, 2928, 2866, 1723, 1644, 1462, 1380, 1188, 1096,
890 cm–1.
MS (EI, 70 eV): m/z (%) = 445 (22) [M]+, 311 (31), 282 (9), 204
(18), 187 (50), 160 (63), 151 (82), 135 (100).
1H NMR (300 MHz, CDCl3): d = 4.73–4.70 (m, 1 H), 4.60 (d,
J = 1.8 Hz, 1 H), 3.84 (s, 2 H), 3.28 (s, 3 H), 2.81 (s, 2 H), 2.19–2.11
(m, 2 H), 2.01–1.94 (m, 2 H), 1.67 (s, 3 H), 1.50–1.23 (m, 8 H), 0.91
(t, J = 7.1 Hz, 3 H), 0.90 (t, J = 7.2 Hz, 3 H). Additional signals of
the minor isomer 17f: d = 4.75–4.73 (m, 1 H), 4.66 (d, J = 1.6 Hz, 1
H), 3.96 (s, 2 H), 3.29 (s, 3 H), 2.75 (s, 2 H), 2.09–2.01 (m, 2 H).
13C NMR (75 MHz, CDCl3): d = 147.4, 137.3, 127.5, 109.3, 70.7,
57.7, 36.7, 36.2, 33.9, 31.1, 30.1, 22.7, 22.4, 18.6, 14.0, 13.9. Addi-
tional signals of the minor isomer 17f: d = 147.0, 136.1, 127.8,
108.7, 72.7, 57.3, 39.1, 36.1, 31.7, 31.6, 22.8, 16.2.
HRMS (EI): m/z [M]+ calcd for C28H35NO2Si: 445.2437;
found: 445.2429.
(4Z)-2-[4-(Methoxymethyl)-5-methyl-2-methylenenon-4-
enyl]isoindoline-1,3-dione (13f) and (4E)-2-[4-(1-Methoxypro-
pan-2-ylidene)-2-methyleneoctyl]isoindoline-1,3-dione (14f)
Eluent: pentane–Et2O, 5:1; white solid; combined yield: 63 mg
(0.18 mmol, 58%); ratio (13f/14f) = 75:25; Rf = 0.14 (pentane–
Et2O, 5:1).
IR (KBr): 2923, 1774, 1716, 1425, 1392, 1190, 1087, 957, 906, 714
cm–1.
MS (EI, 70 eV): m/z (%) = 238 (5) [M]+, 206 (28), 181 (19), 163
(71), 149 (64), 141 (21), 135 (17), 121 (28).
HRMS (EI): m/z [M]+ calcd for C16H30O: 238.2297;
found: 238.2304.
1H NMR (300 MHz, CDCl3): d = 7.87–7.80 (m, 2 H), 7.75–7.67 (m,
2 H), 4.85–4.73 (m, 2 H), 4.20 (s, 2 H), 3.85 (s, 2 H), 3.23 (s, 3 H),
2.90 (s, 2 H), 2.15–2.01 (m, 2 H), 1.66 (s, 3 H), 1.38–1.22 (m, 4 H),
0.91–0.81 (m, 3 H). Additional signals of the minor isomer 14f:
d = 3.93 (s, 2 H), 3.26 (s, 3 H), 2.84 (s, 2 H).
13C NMR (75 MHz, CDCl3): d = 167.9, 141.1, 138.1, 133.8, 132.1,
126.4, 123.2, 110.5, 70.5, 57.8, 42.2, 34.7, 34.0, 31.0, 22.7, 18.7,
14.0. Additional signals of the minor isomer 14f: d = 140.7, 134.7,
133.9, 132.0, 128.9, 123.3, 111.1, 72.6, 57.4, 37.2, 31.6, 31.4, 22.8,
16.3, 13.9.
(5Z)-6-[(Methoxymethoxy)methyl]-5-methyl-8-methylene-
dodec-5-ene (16g) and (5E)-5-[1-(Methoxymethoxy)propan-2-
ylidene]-7-methyleneundecane (17g)
Eluent: pentane–EtOAc, 1:1; yellow oil; combined yield: 34 mg
(0.13 mmol, 20%); ratio (16g/17g) = 72:28; Rf = 0.78 (pentane–
EtOAc, 1:1).
IR (neat): 2957, 2929, 2873, 1642, 1463, 1380, 1149, 1100, 1046,
921, 890 cm–1.
MS (EI, 70 eV): m/z (%) = 341 (12) [M]+, 309 (6), 252 (8), 181 (5),
160 (100), 149 (49), 133 (24), 119 (74).
1H NMR (300 MHz, CDCl3): d = 4.72 (s, 1 H), 4.63–4.59 (m, 3 H),
3.99 (s, 2 H), 3.37 (s, 3 H), 2.83 (s, 2 H), 2.20–2.11 (m, 2 H), 2.02–
1.92 (m, 2 H), 1.68 (s, 3 H), 1.49–1.23 (m, 8 H), 0.91 (t, J = 7.0 Hz,
3 H), 0.90 (t, J = 7.2 Hz, 3 H). Additional signals of the minor iso-
mer 17g: d = 4.65 (s, 1 H), 3.39 (s, 3 H), 2.75 (s, 2 H), 2.09–2.02 (m,
2 H), 1.70 (s, 3 H).
13C NMR (75 MHz, CDCl3): d = 147.4, 138.0, 126.9, 109.0, 95.7,
65.7, 55.1, 37.0, 36.2, 34.0, 31.2, 30.1, 22.8, 22.5, 18.7, 14.0, 13.9.
Additional signals of the minor isomer 17g: d = 147.1, 136.7, 127.2,
109.4, 95.4, 67.8, 39.1, 31.8, 31.7, 22.9, 16.7.
HRMS (EI): m/z [M]+ calcd for C21H27NO3: 341.1991;
found: 341.1994.
The isolation of compounds 16b,17b and 16c,17c was complicated
due to their low polarity and the presence of impurities. The Rf val-
ues of these products were relatively high and purification to an ac-
ceptable level could not achieved. The purity of the compounds
obtained was ~90%. The ratios were determined by GC analysis.
(2E)-(3-Butyl-2-methyl-5-methylenenon-2-enyl)triethylsilane
(17e) and (2Z)-Triethyl[2-(hexan-2-ylidene)-4-methyleneoc-
tyl]silane (16e)
MS (EI, 70 eV): m/z (%) = 268 (3) [M]+, 223 (7), 206 (22), 194 (28),
Eluent: pentane–EtOAc, 1:1; brown oil; combined yield: 64 mg
(0.20 mmol, 40%); ratio (17e/16e) = 60:40; Rf = 0.90 (pentane–
EtOAc, 1:1).
177 (20), 163 (40), 149 (50), 121 (25).
HRMS (EI): m/z [M]+ calcd for C17H32O2: 268.2402;
found: 268.2406.
IR (neat): 2956, 2929, 2876, 1644, 1462, 1380, 1237, 1165, 1014,
889, 738 cm–1.
(5Z)-1-Bromo-6-(methoxymethyl)-5-methyl-8-methylene-
dodec-5-ene (16h) and (5E)-1-Bromo-5-(1-methoxypropan-2-
ylidene)-7-methyleneundecane (17h)
Eluent: pentane–EtOAc, 1:1; brown oil; combined yield: 130 mg
(0.41 mmol, 82%); ratio (16h/17h) = 72:28.
1H NMR (300 MHz, CDCl3): d = 4.74–4.68 (m, 1 H), 4.67 (br s, 1
H), 2.71 (s, 2 H), 2.01–1.88 (m, 4 H), 1.64–1.50 (m, 3 H), 1.49–1.23
(m, 10 H), 1.01–0.84 (m, 15 H), 0.55 (q, J = 7.5 Hz, 6 H). Addition-
al signals of the minor isomer 16e: d = 2.64 (s, 2 H), 0.64–0.46 (m,
6 H).
13C NMR (75 MHz, CDCl3): d = 148.5, 127.8, 127.7, 108.9, 38.6,
36.0, 32.2, 30.5, 30.2, 23.1, 22.6, 21.1, 20.1, 14.1, 14.0, 7.5, 4.2. Ad-
ditional signals of the minor isomer 16e: d = 147.8, 127.5, 127.2,
108.8, 40.9, 36.1, 34.7, 30.4, 23.0, 22.5, 17.9, 17.3, 14.2, 13.9, 7.4,
4.3.
IR (neat): 2957, 2929, 2867, 1727, 1642, 1459, 1380, 1188, 1095,
953, 890 cm–1.
1H NMR (300 MHz, CDCl3): d = 4.73–4.70 (m, 1 H), 4.59 (d,
J = 1.7 Hz, 1 H), 3.83 (s, 2 H), 3.43 (t, J = 6.8 Hz, 2 H), 3.29 (s, 3
H), 2.82 (s, 2 H), 2.22–1.80 (m, 6 H), 1.68 (s, 3 H), 1.61–1.25 (m, 6
H), 0.90 (t, J = 7.2 Hz, 3 H). Additional signals of the minor isomer
17h: d = 4.76–4.73 (m, 1 H), 4.66 (d, J = 1.5 Hz, 1 H), 3.95 (s, 2 H),
3.30 (s, 3 H), 2.76 (s, 2 H).
MS (EI, 70 eV): m/z (%) = 322 (8) [M]+, 293 (7), 115 (100), 107 (5),
87 (99), 73 (5), 59 (69), 55 (6).
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668
G. Hilt, S. Roesner
PAPER
13C NMR (75 MHz, CDCl3): d = 147.3, 136.4, 128.6, 109.5, 70.8,
57.9, 37.0, 36.2, 33.6, 33.2, 32.5, 30.0, 27.1, 22.4, 18.5, 13.9. Addi-
tional signals of the minor isomer 17h: d = 146.9, 135.2, 128.3,
108.9, 72.8, 57.5, 39.0, 36.0, 33.5, 32.7, 30.9, 27.6, 16.4.
IR (KBr): 2960, 2832, 1732, 1574, 1553, 1453, 1407, 1338, 1195,
1125, 1058, 999, 931, 814 cm–1.
1H NMR (300 MHz, CDCl3): d = 6.32 (s, 1 H), 4.19 (s, 2 H), 3.46
(s, 3 H), 2.58 (t, J = 7.6 Hz, 2 H), 1.71 (quin, J = 7.6 Hz, 2 H), 1.40
(sext, J = 7.3 Hz, 2 H), 0.94 (t, J = 7.3 Hz, 3 H).
MS (EI, 70 eV): m/z (%) = 316 (2) [M]+, 286 (13), 255 (12), 243
(20), 229 (43), 219 (37), 205 (21), 181 (22), 163 (62), 149 (34).
HRMS (EI): m/z [M]+ calcd for C16H29OBr: 316.1402;
13C NMR (75 MHz, CDCl3): d = 198.3, 191.3, 97.8, 72.2, 59.6,
37.8, 27.8, 22.2, 13.6.
found: 316.1405.
19F NMR (376 MHz, CDCl3): d = –138.12 (s), –138.18 (s).
11B NMR (128 MHz, CDCl3): d = 0.83 (br s).
MS (EI, 70 eV): m/z (%) = 220 (3) [M]+, 200 (10), 175 (100), 171
(10), 149 (24), 128 (8), 117 (10), 91 (33), 85 (38), 79 (20), 57 (40).
HRMS (EI): m/z [M]+ calcd for C9H1511BF2O3: 220.1082; found:
Ozonolysis; General Procedure
A Schlenk flask, fitted with a glass tube to admit ozone, was
charged with the 1,4-dienes (0.5 mmol) and anhydrous CH2Cl2 (6.0
mL). The reaction mixture was cooled to –78 °C and ozone in a
stream of oxygen was bubbled through the solution. When the solu-
tion turned blue, ozone addition was stopped. By passing oxygen
through the solution the excess of ozone was removed and dimethyl
sulfide (62 mg, 1.00 mmol) was added. The solution was allowed to
warm to r.t. and after stirring for 1 h, BF3·OEt2 (214 mg, 1.50 mmol)
was slowly added to the reaction mixture and stirred at r.t. for 16 h.
The solvent was removed under reduced pressure and the residue
was purified by flash column chromatography using EtOAc–pen-
tane as eluent.
220.1100.
Acknowledgment
Financial support by the Deutsche Forschungsgemeinschaft is
acknowledged.
References
2-[(2¢,2¢-Difluoro-6¢-butyl-1¢,3¢,2¢-dioxaborinine-4-yl)meth-
yl]isoindoline-1,3-dione (19a)
Eluent: pentane–EtOAc, 1:1; brown solid; yield: 10 mg (30 mmol,
25%); Rf = 0.50 (pentane–EtOAc, 1:1).
(1) For recent reviews, see: (a) Leboeuf, D.; Gandon, V.;
Malacria, M. In Handbook of Cyclization Reactions, Vol. 1;
Ma, S., Ed.; Wiley-VCH: Weinheim, 2009, 367. (b) Galan,
B. R.; Rovis, T. Angew. Chem. Int. Ed. 2009, 48, 2830.
(c) Omae, I. Appl. Organomet. Chem. 2008, 22, 149.
(d) Hess, W.; Treutwein, J.; Hilt, G. Synthesis 2008, 3537.
(e) Omae, I. Appl. Organomet. Chem. 2007, 21, 318.
(f) Kotha, S.; Brahmachary, E.; Lahiri, K. Eur. J. Org.
Chem. 2005, 4741. (g) Malacria, M.; Aubert, C.; Renaud, J.
L. In Science of Synthesis: Houben-Weyl Methods of
Molecular Transformations, Vol. 1; Lautens, M.; Trost, B.
M., Eds.; Thieme: Stuttgart, 2001, 439. (h) Saito, S.;
Yamamoto, Y. Chem. Rev. 2000, 100, 2901.
(2) (a) Hilt, G.; du Mesnil, F.-X.; Lüers, S. Angew. Chem. Int.
Ed. 2001, 40, 387. (b) Hilt, G.; Lüers, S. Synthesis 2002,
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(d) Hilt, G.; Danz, M.; Treutwein, J. Org. Lett. 2009, 11,
3322. (e) Hilt, G.; Treutwein, J. Chem. Commun. 2009,
1395. (f) Arndt, M.; Reinhold, A.; Hilt, G. J. Org. Chem.
2010, 75, 5203. (g) Sharma, R. K.; RajanBabu, T. V. J. Am.
Chem. Soc. 2010, 132, 3295. (h) Saha, B.; Smith, C. R.;
RajanBabu, T. V. J. Am. Chem. Soc. 2008, 130, 9000.
(i) Shirakura, M.; Suginome, M. J. Am. Chem. Soc. 2008,
130, 5410. (j) Saha, B.; RajanBabu, T. V. J. Org. Chem.
2007, 72, 2357. (k) Zhang, A.; RajanBabu, T. V. J. Am.
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Org. Lett. 2004, 6, 1515. (m) Zhang, A.; RajanBabu, T. V.
Org. Lett. 2004, 6, 3159. (n) Kumareswaran, R.; Nandi, M.;
RajanBabu, T. V. Org. Lett. 2003, 5, 4345. (o) Moreau, B.;
Wu, J. Y.; Ritter, T. Org. Lett. 2009, 11, 337.
IR (KBr): 2960, 1777, 1721, 1551, 1416, 1392, 1193, 1059, 993,
947, 796, 715 cm–1.
1H NMR (300 MHz, CDCl3): d = 7.95–7.87 (m, 2 H), 7.83–7.73 (m,
2 H), 5.97 (s, 1 H), 4.65 (s, 2 H), 2.53 (t, J = 7.6 Hz, 2 H), 1.67
(quin, J = 7.5 Hz, 2 H), 1.37 (sext, J = 7.3 Hz, 2 H), 0.91 (t,
J = 7.3 Hz, 3 H).
13C NMR (75 MHz, CDCl3): d = 198.7, 187.0, 167.0, 134.7, 131.6,
124.0, 98.4, 41.1, 37.8, 27.6, 22.2, 13.6.
19F NMR (376 MHz, CDCl3): d = –137.70 (s), –137.76 (s).
11B NMR (128 MHz, CDCl3): d = 0.57 (br s).
MS (ESI): m/z (%) = 358 (5) [M + Na]+, 327 (5), 311 (100), 295
(18), 266 (5), 244 (5), 203 (5), 130 (44), 118 (5), 102 (16).
HRMS (ESI): m/z [M + Na]+ calcd for C16H1611BF2NO4Na:
358.1033; found: 358.1031.
2,2-Difluoro-4,6-dibutyl-1,3,2-dioxaborinine (19b)
Eluent: pentane–EtOAc, 1:1; brown oil; yield: 13 mg (54 mmol,
28%); Rf = 0.84 (pentane–EtOAc, 1:1).
IR (KBr): 2961, 2874, 1721, 1552, 1466, 1408, 1189, 1112, 1056,
994, 807 cm–1.
1H NMR (300 MHz, CDCl3): d = 5.93 (s, 1 H), 2.50 (t, J = 7.6 Hz,
4 H), 1.68 (quin, J = 7.6 Hz, 4 H), 1.39 (sext, J = 7.4 Hz, 4 H), 0.93
(t, J = 7.3 Hz, 6 H).
(p) Grabulosa, A.; Muller, G.; Ordinas, J. I.; Mezzetti, A.;
Maestro, M. A.; Font-Bardia, M.; Solans, X.
Organometallics 2005, 24, 4961.
13C NMR (75 MHz, CDCl3): d = 195.7, 100.3, 37.3, 27.8, 22.2, 13.6.
11B NMR (128 MHz, CDCl3): d = 0.63 (br s).
19F NMR (376 MHz, CDCl3): d = –139.09 (s), –139.15 (s).
MS (ESI): m/z (%) = 255 (31) [M + Na]+, 225 (10), 218 (25), 207
(22), 185 (65), 139 (7), 130 (4).
(3) (a) Hilt, G.; Weske, D. F. Chem. Soc. Rev. 2009, 38, 3082.
(b) Hilt, G.; Treutwein, J. Chem. Commun. 2009, 1395.
(c) Hilt, G.; Arndt, M.; Weske, D. F. Synthesis 2010, 1321.
(4) For selected recent applications, see: (a) Diver, S. T.;
Giessert, A. J. Chem. Rev. 2004, 104, 1317. (b) Mori, M.
Adv. Synth. Catal. 2007, 349, 121. (c) Mix, S.; Blechert, S.
Org. Lett. 2005, 7, 2015. (d) Bentz, D.; Laschat, S.
Synthesis 2000, 1766. (e) Danz, M.; Hilt, G. Adv. Synth.
Catal. 2011, in press.
HRMS (ESI): m/z [M + Na]+ calcd for C11H1911BF2O2Na:
255.1338; found: 255.1340.
2,2-Difluoro-6-butyl-4-methoxymethyl-1,3,2-dioxaborinine
(18c)
Eluent: pentane–EtOAc, 1:1; brown oil; yield: 10 mg (47 mmol,
11%); Rf = 0.73 (pentane–EtOAc, 1:1).
Synthesis 2011, No. 4, 662–668 © Thieme Stuttgart · New York