Mild double allylboration reactions of nitriles and acid anhydrides using potassium allyltrifluoroborate

Article abstract of DOI:10.1021/jo302194n

The double allylboration of nitriles and acid anhydrides to form bis-allyl amines and esters, respectively, can be achieved through the use of potassium allyltrifluoroborate in the presence of boron trifluoride etherate at room temperature. The method described is relatively mild, exhibits chemoselectivity to other electrophiles present, avoids the use of metals, and features the use of an operationally stable and robust potassium organotrifluoroborate reagent.

Full text of DOI:10.1021/jo302194n

Note
pubs.acs.org/joc
Mild Double Allylboration Reactions of Nitriles and Acid Anhydrides
Using Potassium Allyltrifluoroborate
Timothy R. Ramadhar, Jazmin Bansagi, and Robert A. Batey*
Davenport Research Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, Canada,
M5S 3H6
S
* Supporting Information
ABSTRACT: The double allylboration of nitriles and acid anhydrides to form bis-
allyl amines and esters, respectively, can be achieved through the use of potassium
allyltrifluoroborate in the presence of boron trifluoride etherate at room
temperature. The method described is relatively mild, exhibits chemoselectivity
to other electrophiles present, avoids the use of metals, and features the use of an
operationally stable and robust potassium organotrifluoroborate reagent.
he double allylation of electrophiles at the carboxyl
oxidation state provides a manner to access bisallylic
mild and selective allylation of aldehydes and ketones16 or
imines.17 More recently, allyl-BF3K has been shown to allylate
the C2 position of indoles in very good yields.18 Given the
success of allyl-BF3K addition to indoles, we believed that these
reagents could exhibit reactivity toward other similarly less
reactive electrophiles. Herein, we disclose the application of
these reagents toward the mild and chemoselective metal-free
allylation of nitriles and acid anhydrides.
The reaction of allyl-BF3K with BF3·OEt2 and carbonyl
compounds and imines under anhydrous conditions presum-
ably occurs via in situ-generated allyl-BF2 as the active allylating
agent.16a,b,17−19 We considered that such an in situ-generated
allyl-BF2 species would be much more reactive than
allylboronic ester equivalents and could have sufficient
reactivity to add to functionalities at the carboxyl oxidation
state. A general strategy involving the allylation of acid
anhydrides or nitriles using allyl-BF3K with BF3·OEt2 activation
was therefore envisioned. At least 2 equiv of the allyl-BF3K
reagent would be required, as previously observed for other
systems,16a,b,17,18 because the in situ-generated allyl-BF2 may
decompose during the course of the reaction, and an excess
may ensure that enough active allylating reagent is available.
Accordingly, reactions of nitriles could be achieved using 4
equiv of allyl-BF3K and 5 equiv of BF3·OEt2 in CH2Cl2 for 6 h.
The parent benzonitrile (1a) substrate was doubly allylated to
furnish 2a in 87% yield (Table 1).
T
compounds. These substrates can form the basis to obtain
synthetically interesting compounds, including spirocycles
through ring closing metathesis (RCM).1 Typically, function-
alities in the carboxyl oxidation state are intrinsically less
reactive toward nucleophilic attack than functional groups at
the carbonyl oxidation state, such as aldehydes, ketones, and
imines, due to heteroatomic mesomeric stabilization of the
electrophilic carboxylate center, or through additional π-
electron stabilization as observed in nitriles. As a result,
methods to allylate functional groups such as nitriles and acid
anhydrides typically involve the overstoichiometric use of
reactive allyl metal species, including Grignard reactions,2
Grignard-type conditions using samarium,3,4 indium,5 or zinc,6
or Barbier reactions using aluminum/lead,7 zinc/copper,8 or
indium.9,10
It was envisaged that allylboration could afford a mild,
inexpensive, and environmentally benign metal-free method to
allylate nitriles and acid anhydrides, especially for substrates
with functional groups that may not be tolerant of metal-based
allylating reagents. The allylboration of acid anhydrides was
investigated by Kramer and Brown using the sensitive B-allyl-9-
BBN reagent.11 Additionally, the allylboration of nitriles has
been reported by Bubnov and co-workers;12 however, the
method employs triallylborane, which is inconvenient to use,
and required forcing thermal conditions to form the diaza-2,4-
diboretidine product, which could presumably be further
reacted to furnish the bisallylamine. While operationally simpler
organoboronic ester derivatives can be used for the allylation of
carbonyl13 and imine13f,14 compounds, to the best of our
knowledge, there is no precedence for the direct implementa-
tion of these reagents toward the allylation of nitriles or acid
anhydrides. Our laboratory has previously demonstrated that
potassium allyltrifluoroborate (allyl-BF3K) and related salts15
act as surrogates for allylboronic acids and esters, achieving the
The method is tolerant of a variety of substituents on the
aromatic ring. Notably, the ester (1i), isothiocyanate (1j), and
sulfonamide (1k) functional groups can withstand the reaction
conditions. However, lower yields are observed for substrates
bearing either mesomerically electron-donating substituents on
the para position of the aromatic ring or ortho-substituents, as
observed for the reactions of 1d, 1f, and 1h. Yields were also
Received: October 5, 2012
Published: December 6, 2012
© 2012 American Chemical Society
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Note
Table 1. Double Allylboration of Nitriles
lower for substrates where the nitrile group was not directly
appended to an aryl ring (e.g., 1l, 1m, 1p). An indole-based
nitrile substrate (1n) was also suitable for reaction, and double
allylboration of the nitrile functionality was successful in the
presence of a pyridine ring (1o).
The formation of in situ-generated allyl-BF2 is necessary as
shown by a control allylation experiment involving nitrile 1a,
where water was added to form allyl-B(OH)2, and for which
none of the bis-allylated product 2a was observed (Scheme 1).
An attempt to adapt and apply previously reported allylation
conditions using Montmorillonite K10 activation16e on nitrile
1a was made (double the quantity of Montmorillonite K10 and
CH2Cl2/H2O solvent from the reported ketone allylation
conditions were employed). Compound 2a was obtained, but
the yield was much lower (21%) than that obtained through
BF3·OEt2 activation.
Given the observed success with nitrile substrates, focus was
then placed upon the use of acid anhydride substrates. It was
observed that a modification of the conditions employed for
double allylboration of nitriles, using 5 equiv of allyl-BF3K and
5 equiv of BF3·OEt2 in CH2Cl2 solvent for 2 h, allowed for the
successful double allylboration of phthalic anhydride (3a) in
excellent yield to furnish 4a (92%) (Table 2). Other aliphatic
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Note
alternative for the previously reported Barbier or Grignard-
based double allylation procedures. Finally, this method
illustrates the general concept of using Lewis acid activation
to achieve the addition of allyltrifluoroborate salts to electro-
philes of low intrinsic reactivity.
Scheme 1. Control Double Allylboration Experiment of a
Nitrile Using H2O (above) and Montmorillonite K10
Activation (below)
EXPERIMENTAL SECTION
■
General Information. Reagents obtained from commercial
suppliers were used as received. CH2Cl2 was distilled under nitrogen
from calcium hydride through standard techniques. Compounds were
typically purified using silica gel flash chromatography (silica: 60 Å,
230−400 mesh). Analytical thin layer chromatography (TLC) was
performed on precoated UV-active aluminum backed silica plates,
visualized with a UV254 lamp, and stained with 20% phosphomolybdic
acid in ethanol. IR spectra were run as thin films (neat or with CDCl3)
on NaCl plates. Mass spectral data were obtained through DART
(direct analysis in real time) or ESI methods. All melting points that
Table 2. Double Allylboration of Acid Anhydrides
1
were obtained are uncorrected. The H and 13C NMR spectra of all
compounds were obtained at 400 and 100 MHz, respectively.
Chemical shifts are reported in parts per million (δ) and coupling
1
constants (J) are reported in hertz (Hz). The H NMR spectra were
referenced to the TMS internal standard, while 13C NMR spectra were
referenced to CDCl3 (δ 73.23). NMR experiments were performed at
25 °C unless otherwise stated. The multiplicities of the signals are
indicated via the following abbreviations: s, singlet; d, doublet; t,
triplet; q, quartet; m, multiplet. If a coupling pattern can be assigned as
a combination of multiplicities, then the listed abbreviations are
combined to provide an appropriate descriptor for the observed
patterns (e.g., dt, doublet of triplets). Signals that have singlet
multiplicity and are deemed as broad are prefixed with “br”.
N-(4-Cyanophenyl)-4-methylbenzenesulfonamide (1k).21 To a
round-bottom flask were added 4-aminobenzonitrile (0.49 g, 4.1
mmol), 4-toluenesulfonyl chloride (0.79 g, 4.1 mmol), pyridine (20
mL), and a magnetic stirrer. The solution was heated to reflux for 3
days and stirred under an atmosphere of nitrogen. The solution was
subsequently concentrated in vacuo, and the crude mixture was
dissolved in EtOAc (75 mL). The organic phase was washed with HCl
(aq, 3 N, 4 × 50 mL) and with a saturated NaHCO3 solution (2 × 50
mL). The organic phase was then dried with Na2SO4, and the solvent
was removed under reduced pressure to afford 1k (0.74 g, 65%) as a
light brown solid that did not require further purification. Mp 184−
1
186 °C (EtOAc); H NMR (400 MHz, DMSO-d6): δ 10.97 (1H, br
s), 7.73−7.67 (4H, m), 7.38 (2H, d, J = 8.0 Hz), 7.25−7.22 (2H, m),
2.34 (3H, s); 13C NMR (100 MHz, DMSO-d6): δ 143.9, 142.3, 136.2,
133.6, 129.9, 126.7, 118.7, 118.4, 105.3, 21.0.
Double Allylboration of Nitriles. To a round-bottom flask
equipped with a magnetic stirrer and charged with potassium
allyltrifluoroborate (2.0 mmol, 4.0 equiv) were added CH2Cl2 (5
mL) and nitrile 1 (0.50 mmol, 1.0 equiv). BF3·OEt2 (2.5 mmol, 5.0
equiv) was subsequently added dropwise, and the mixture was stirred
at room temperature under an N2 atmosphere. After 6 h, starting
material conversion was confirmed through TLC analysis, and
approximately five drops of HCl (aq, 1 N) was added to facilitate
hydrolysis of any potential amino-borate adduct present, followed by
saturated NaHCO3 solution (5 mL). Deionized water (∼5−10 mL)
was added as necessary to facilitate phase separation, and the organic
phase was obtained. The aqueous phase was subsequently extracted
with CH2Cl2 (3 × 5 mL), and the combined organic layers were dried
over anhydrous Na2SO4. After evaporation of the solvent, the crude
mixture was purified through silica gel flash chromatography.
cyclic acid anhydrides underwent bis-allylation in excellent
yields using the same mild conditions.20
In conclusion, the double allylboration of nitriles and acid
anhydrides can be achieved under mild conditions using
potassium allyltrifluoroborate in the presence of BF3·OEt2. This
method circumvents some of the operational disadvantages of
previous allylborane-based approaches and occurs at ambient
temperature, rather than the elevated temperatures required for
triallylboron, using a much more stable and conveniently
handled potassium allyltrifluoroborate reagent. It is likely that
the BF3·OEt2 Lewis acid generates allyldifluoroborane as the
reactive allylating species. Overall, the method is tolerant of
other electrophilic functional groups that may be present in the
substrate at ambient temperature. It is envisaged that this
approach will either complement or serve as a suitable
4-Phenylhepta-1,6-dien-4-amine (2a). Using the standard nitrile
double allylboration procedure and flash chromatography on silica gel
(45% EtOAc/hexanes + 0.5% NEt3) afforded 2a (0.082 g, 87%) as a
yellow oil. Rf = 0.23 (40% EtOAc/hexanes); IR (thin film) νmax 3374,
3312, 3075, 3024, 3005, 2977, 2914, 2855, 1700, 1637, 1601, 999, 917,
1
832, 765, 701 cm−1; H NMR (400 MHz, CDCl3): δ 7.44−7.41 (2H,
m), 7.36−7.31 (2H, m), 7.24−7.20 (1H, m), 5.52 (2H, dddd, J = 17.0,
10.0, 8.5, 6.0 Hz), 5.10−5.02 (4H, m), 2.66 (2H, dddd, J = 13.5, 6.0,
1.5, 1.5 Hz), 2.44−2.38 (2H, m), 1.60 (2H, br s); 13C NMR (100
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Note
MHz, CDCl3): δ 146.8, 134.1, 128.3, 126.4, 126.0, 118.8, 57.1, 48.3;
LRMS (DART+) m/z (rel intensity) 188.1 (60) [M + H]+, 171.1
(100); HRMS (DART+) m/z calcd for C13H18N [M + H]+: 188.1439.
Found: 188.1438.
207.1 (29), 205.1 (100); HRMS (DART+) m/z calcd for C13H17ClN
[M + H]+: 222.1050. Found: 222.1050.
4-(3-Chlorophenyl)hepta-1,6-dien-4-amine (2g). Using the stand-
ard nitrile double allylboration procedure and flash chromatography
on silica gel (60% EtOAc/hexanes + 0.5% NEt3) afforded 2g (0.079 g,
71%) as a yellow oil. Rf = 0.58 (80% EtOAc/hexanes); IR (thin film)
νmax 3375, 3314, 3076, 3005, 2978, 2914, 2854, 1640, 1595, 1570,
1478, 1442, 1417, 1341, 1296, 1184, 1080, 998, 919, 840, 784, 705
cm−1; 1H NMR (300 MHz, CDCl3): δ 7.44 (1H, dd, J = 1.5, 1.5 Hz),
7.32−7.18 (3H, m), 5.50 (2H, dddd, J = 16.5, 10.0, 8.0, 6.0 Hz), 5.11−
5.04 (4H, m), 2.62 (2H, dddd, J = 12.5, 6.0, 1.5, 1.5 Hz), 2.43−2.35
(2H, m), 1.74 (2H, br s); 13C NMR (75 MHz, CDCl3): δ 149.2, 134.4,
133.5, 129.5, 126.6, 126.5, 124.3, 119.3, 57.1, 48.1; LRMS (DART+)
m/z (rel intensity) 224.1 (30), 222.1 (99) [M + H]+, 207.1 (24),
205.1 (100); HRMS (DART+) m/z calcd for C13H17ClN [M + H]+:
222.1050. Found: 222.1056.
4-(4-Nitrophenyl)hepta-1,6-dien-4-amine (2b). Using the stand-
ard nitrile double allylboration procedure and flash chromatography
on silica gel (80% EtOAc/hexanes + 0.5% NEt3) afforded 2b (0.090 g,
78%) as an orange oil. Rf = 0.53 (EtOAc); IR (thin film) νmax 3374,
3312, 3077, 3005, 2978, 2916, 2853, 1640, 1601, 1514, 1491, 1441,
1348, 1109, 997, 920, 854, 706 cm−1; 1H NMR (400 MHz, CDCl3): δ
8.21−8.17 (2H, m), 7.66−7.62 (2H, m), 5.54−5.44 (2H, m), 5.10−
5.06 (4H, m), 2.67 (2H, dddd, J = 14.0, 6.5, 1.0, 1.0 Hz), 2.47−2.42
(2H, m), 1.55 (2H, br s); 13C NMR (100 MHz, CDCl3): δ 154.7,
146.7, 132.9, 127.3, 123.5, 119.8, 57.7, 46.2; LRMS (ESI+) m/z (rel
intensity) 233.1 (52) [M + H]+, 216.1 (100); HRMS (ESI+) m/z calcd
for C13H17N2O2 [M + H]+: 233.1284. Found: 233.1279.
4-(3-Nitrophenyl)hepta-1,6-dien-4-amine (2c). Using the standard
nitrile double allylboration procedure and flash chromatography on
silica gel (60% EtOAc/hexanes + 0.5% NEt3) afforded 2c (0.092 g,
79%) as a yellow oil. Rf = 0.56 (80% EtOAc/hexanes); IR (thin film)
νmax 3374, 3312, 3077, 3005, 2978, 2916, 2861, 1640, 1527, 1443,
1348, 1314, 1288, 1099, 1078, 998, 920, 807, 703 cm−1; 1H NMR (400
MHz, CDCl3): δ 8.36 (1H, dd, J = 2.0, 2.0 Hz), 8.09 (1H, ddd, J = 8.0,
2.0, 1.0 Hz), 7.82 (1H, ddd, J = 8.0, 2.0, 1.0 Hz), 7.52 (1H, dd, J = 8.0,
8.0 Hz), 5.56−5.46 (2H, m), 5.11−5.07 (4H, m), 2.67 (2H, dddd, J =
13.5, 6.5, 1.5, 1.5 Hz), 2.44 (2H, m), 1.73 (2H, br s); 13C NMR (100
MHz, CDCl3): δ 149.4, 148.5, 132.9, 132.5, 129.2, 121.6, 121.3, 119.8,
57.3, 48.0; LRMS (DART+) m/z (rel intensity) 233.1 (100) [M +
H]+, 216.1 (19); HRMS (DART+): m/z [M + H]+ calcd for
C13H17N2O2: 233.1290; found: 233.1292.
4-(2-Chlorophenyl)hepta-1,6-dien-4-amine (2h). Using the stand-
ard nitrile double allylboration procedure and flash chromatography
on silica gel (45% EtOAc/hexanes + 0.5% NEt3) afforded 2h (0.031 g,
28%) as a yellow oil. Rf = 0.65 (50% EtOAc/hexanes); IR (thin film)
νmax 3372, 3312, 3074, 2977, 2925, 2870, 1640, 1591, 1464, 1432,
1291, 1036, 997, 917, 757, 743 cm−1; 1H NMR (400 MHz, CDCl3): δ
7.60 (1H, dd, J = 7.5, 2.0 Hz), 7.36 (1H, dd, J = 7.5, 1.5 Hz), 7.23 (1H,
ddd, J = 7.5, 7.5, 1.5 Hz), 7.17 (1H, ddd, J = 7.5, 7.5, 2.0 Hz), 5.48
(2H, dddd, J = 17.0, 10.0, 8.5, 6.5 Hz), 5.11−5.06 (2H, m), 5.02−4.99
(2H, m), 3.23 (2H, dddd, J = 14.0, 6.5, 1.5, 1.5 Hz), 2.52−2.47 (2H,
m), 1.93 (2H, br s); 13C NMR (100 MHz, CDCl3): δ 142.9, 134.1,
132.1, 131.9, 129.6, 128.3, 126.9, 118.7, 58.3, 44.6; LRMS (DART+)
m/z (rel intensity) 224.1 (33), 222.1 (100) [M + H]+, 205.1 (21),
186.1 (18), 182.1 (21), 180.1 (68); HRMS (DART+) m/z calcd for
C13H17ClN [M + H]+: 222.1050. Found: 222.1059.
Methyl 4-(4-Aminohepta-1,6-dien-4-yl)benzoate (2i). Using the
standard nitrile double allylboration procedure and flash chromatog-
raphy on silica gel (50% EtOAc/hexanes + 0.5% NEt3) afforded 2i
(0.098 g, 80%) as a yellow oil. Rf = 0.33 (50% EtOAc/hexanes); IR
(thin film) νmax 3375, 3317, 3076, 3003, 2977, 2950, 2914, 2844, 1723,
1640, 1610, 1435, 1407, 1280, 1191, 1108, 1018, 918, 854, 827, 775,
712 cm−1; 1H NMR (400 MHz, CDCl3): δ 8.02−7.99 (2H, m), 7.53−
7.50 (2H, m), 5.49 (2H, dddd, J = 17.0, 10.0, 8.5, 6.5 Hz), 5.09−5.03
(4H, m), 3.91 (3H, s), 2.66 (2H, dddd, J = 13.5, 6.5, 1.5, 1.5 Hz),
2.45−2.39 (2H, m), 1.62 (2H, br s); 13C NMR (100 MHz, CDCl3): δ
167.2, 152.3, 133.5, 129.6, 128.4, 126.2, 119.3, 57.5, 52.2, 48.2; LRMS
(DART+) m/z (rel intensity) 246.2 (100) [M + H]+, 229.1 (49);
HRMS (DART+) m/z calcd for C15H20NO2 [M + H]+: 246.1494.
Found: 246.1498.
4-(4-Methoxyphenyl)hepta-1,6-dien-4-amine (2d). Using the
standard nitrile double allylboration procedure and flash chromatog-
raphy on silica gel (60% EtOAc/hexanes + 0.5% NEt3) afforded 2d
(0.052 g, 47%) as a yellow oil. Rf = 0.30 (70% EtOAc/hexanes); IR
(thin film) νmax 3370, 3312, 3074, 3002, 2976, 2933, 2912, 2835, 1640,
1
1607, 1511, 1505, 1301, 1249, 1180, 1037, 999, 916, 830 cm−1; H
NMR (400 MHz, CDCl3): δ 7.36−7.32 (2H, m), 6.89−6.85 (2H, m),
5.53 (2H, dddd, J = 17.0, 10.0, 8.5, 6.5 Hz), 5.10−5.02 (4H, m), 3.80
(3H, s), 2.61 (2H, dddd, J = 13.5, 6.5, 1.0, 1.0 Hz), 2.42−2.36 (2H,
m), 1.70 (2H, br s); 13C NMR (100 MHz, CDCl3): δ 158.1, 138.9,
134.2, 127.1, 118.8, 113.6, 56.7, 55.4, 48.3; LRMS (DART+) m/z (rel
intensity) 218.2 (57) [M + H]+, 201.1 (100), 176.1 (7); HRMS
(DART+) m/z calcd for C14H20NO [M + H]+: 218.1545. Found:
218.1542.
4-(3-Methoxyphenyl)hepta-1,6-dien-4-amine (2e). Using the
standard nitrile double allylboration procedure and flash chromatog-
raphy on silica gel (60% EtOAc/hexanes + 0.5% NEt3) afforded 2e
(0.074 g, 68%) as a yellow oil. Rf = 0.46 (80% EtOAc/hexanes); IR
(thin film) νmax 3372, 3302, 3075, 3002, 2976, 2935, 2914, 2834, 1640,
1607, 1582, 1484, 1464, 1432, 1290, 1248, 1170, 1051, 997, 917, 782,
705 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.28−7.23 (1H, m), 7.01−
6.98 (2H, m), 6.76 (1H, ddd, J = 8.0, 2.5, 1.0 Hz), 5.53 (2H, dddd, J =
17.0, 10.0, 8.5, 6.0 Hz), 5.11−5.02 (4H, m), 3.81 (3H, s), 2.64 (2H,
dddd, J = 13.5, 6.0, 1.5, 1.5 Hz), 2.42−2.36 (2H, m), 1.62 (2H, br s);
13C NMR (100 MHz, CDCl3): δ 159.7, 148.8, 134.0, 129.2, 118.8,
118.4, 112.5, 111.2, 57.1, 55.4, 48.2; LRMS (DART+) m/z (rel
intensity) 218.2 (81) [M + H]+, 201.1 (100), 176.1 (25); HRMS
(DART+) m/z calcd for C14H20NO [M + H]+: 218.1545. Found:
218.1552.
4-(4-Chlorophenyl)hepta-1,6-dien-4-amine (2f). Using the stand-
ard nitrile double allylboration procedure and flash chromatography
on silica gel (60% EtOAc/hexanes + 0.5% NEt3) afforded 2f (0.62 g,
56%) as a yellow oil. Rf = 0.49 (80% EtOAc/hexanes); IR (thin film)
νmax 3373, 3312, 3076, 3005, 2977, 2916, 2854, 1640, 1593, 1492,
1441, 1398, 1094, 998, 918, 828 cm−1; 1H NMR (400 MHz, CDCl3):
δ 7.39−7.36 (2H, m), 7.31−7.28 (2H, m), 5.51 (2H, dddd, J = 17.0,
10.0, 8.5, 6.5 Hz), 5.10−5.03 (4H, m), 2.61 (2H, dddd, J = 13.5, 6.5,
1.5, 1.5 Hz), 2.41−2.36 (2H, m), 1.53 (2H, br s); 13C NMR (100
MHz, CDCl3): δ 145.4, 133.7, 132.3, 128.4, 127.6, 119.2, 57.0, 48.3;
LRMS (DART+) m/z (rel intensity) 224.1 (24), 222.1 (78) [M + H]+,
4-(4-Isothiocyanatophenyl)hepta-1,6-dien-4-amine (2j). The
standard nitrile double allylboration procedure was used with the
following exceptions in regards to workup: (i) no HCl was used, and
(ii) water was used instead of a saturated solution of NaHCO3.
Additionally, on account of the instability of this compound toward
silica gel flash chromatography, purification was achieved through
trituration using hexanes and 5% CH2Cl2/hexanes to afford 2j (0.101
g, 83%) as a viscous orange oil. IR (thin film) νmax 3579, 3171, 2926,
1
2102, 1609, 1514, 1451, 1344, 1062, 936, 834, 731 cm−1; H NMR
(400 MHz, CDCl3): δ 7.38−7.36 (2H, m), 7.25−7.22 (2H, m), 5.55−
5.44 (2H, m), 5.29−5.22 (4H, m), 2.88−2.83 (2H, m), 2.79−2.73
(2H, m); 13C NMR (100 MHz, CDCl3): δ 137.5, 136.3, 132.1, 129.0,
127.0, 126.5, 123.4, 62.2, 42.6; LRMS (DART+) m/z (rel intensity)
245.1 (12) [M + H]+, 228.1 (100); HRMS (DART+) m/z calcd for
C14H17N2S [M + H]+: 245.1112. Found: 245.1121.
N-(4-(4-Aminohepta-1,6-dien-4-yl)phenyl)-4-methylbenzenesul-
fonamide (2k). Using the standard nitrile double allylboration
procedure and flash chromatography on silica gel (80% EtOAc/
hexanes + 0.5% NEt3) afforded 2k (0.172 g, 96%) as a light beige solid.
Mp 132−134 °C (CDCl3); Rf = 0.33 (EtOAc); IR (thin film in
CDCl3) νmax 3353, 3257, 3075, 3029, 3006, 2978, 2921, 2850, 1639,
1
1599, 1511, 1444, 1335, 1161, 1093, 919, 813, 732, 663 cm−1; H
NMR (400 MHz, CDCl3): δ 7.63−7.60 (2H, m), 7.31−7.28 (2H, m),
7.22−7.19 (2H, m), 7.02−7.00 (2H, m), 6.31 (1H, br s), 5.44 (2H,
dddd, J = 17.0, 11.0, 8.5, 6.5 Hz), 5.05−5.00 (4H, m), 2.59−2.54 (2H,
1219
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The Journal of Organic Chemistry
Note
m), 2.38 (3H, s), 2.38−2.33 (2H, m), 1.49 (2H, br s); 13C NMR (100
MHz, CDCl3): rotameric mixture: δ 144.3, 144.2, 144.0, 136.4, 134.8,
134.7, 133.8, 129.7, 127.5, 127.07, 127.06, 122.0, 121.9, 119.0, 56.9,
48.2, 21.8; LRMS (ESI+) m/z (rel intensity) 379.1 (1) [M + Na]+,
357.2 (1) [M + H]+, 340.1 (100); HRMS (ESI+) m/z calcd for
C20H25N2O2S [M + H]+: 357.1631. Found: 357.1644.
126.6, 118.9, 54.4, 46.5, 44.5; LRMS (ESI+) m/z (rel intensity) 202
(18) [M + H]+, 185 (26), 143 (84), 129 (59), 117 (36), 91 (100);
HRMS (ESI+) m/z calcd for C14H20N [M + H]+: 202.1590. Found:
202.1596.
Double Allylboration of Acid Anhydrides. To a round-bottom
flask equipped with a magnetic stirrer and charged with potassium
allyltrifluoroborate (0.370 g, 2.5 mmol, 5.0 equiv) were added CH2Cl2
(5 mL) and acid anhydride (0.50 mmol, 1.0 equiv). BF3·OEt2 (310 μL,
2.5 mmol, 5.0 equiv) was subsequently added dropwise, and the
mixture was stirred at room temperature under an N2 atmosphere.
After 2 h, starting material conversion was confirmed through TLC,
and approximately five drops of HCl (aq, 1 N) was added followed by
saturated NaHCO3 solution (5 mL). Deionized water (∼5−10 mL)
was added as necessary to facilitate phase separation, and the organic
phase was obtained. The aqueous phase was extracted with CH2Cl2 (3
× 5 mL), and the combined organic layers were dried over anhydrous
Na2SO4. After evaporation of the solvent, the crude mixture was
purified through silica gel flash chromatography.
(E)-4-Styrylhepta-1,6-dien-4-amine (2l). Using the standard nitrile
double allylboration procedure and flash chromatography on silica gel
EtOAc + 0.5% NEt3) afforded 2l (0.092 g, 44%) as a yellow oil. Rf =
0.23 (EtOAc); IR (thin film) νmax 3370, 3293, 3075, 3025, 3003, 2976,
2921, 2856, 1640, 1600, 1494, 1449, 1436, 1415, 1071, 997, 971, 915,
1
749, 693 cm−1; H NMR (400 MHz, CDCl3): δ 7.39−7.37 (2H, m),
7.33−7.29 (2H, m), 7.23−7.20 (1H, m), 6.49 (1H, d, J = 16.0 Hz),
6.27 (1H, d, J = 16.0 Hz), 5.80 (2H, dddd, J = 16.0, 9.5, 8.0, 6.5 Hz),
5.10−5.16 (4H, m), 2.36 (2H, dddd, J = 13.5, 6.5, 6.5, 1.0 Hz), 2.29−
2.24 (2H, m), 1.59 (2H, br s); 13C NMR (100 MHz, CDCl3): δ 137.4,
137.3, 134.0, 128.8, 128.1, 127.5, 126.5, 119.0, 55.7, 46.7; LRMS
(DART+) m/z (rel intensity) 214.2 (22) [M + H]+, 197.1 (100);
HRMS (DART+) m/z calcd for C15H20N [M + H]+: 214.1596. Found:
214.1592.
3,3-Diallylisobenzofuran-1(3H)-one (4a).6 Using the standard acid
anhydride double allylboration procedure and flash chromatography
on silica gel (30% EtOAc/hexanes) afforded 4a (0.099 g, 92%) as a
yellow oil. 1H NMR (400 MHz, CDCl3): δ 7.86 (1H, ddd, J = 7.5, 1.0,
1.0 Hz), 7.60 (1H, ddd, J = 7.5, 7.5, 1.0 Hz), 7.50 (1H, ddd, J = 7.5,
7.5, 1.0 Hz), 7.38 (1H, ddd, J = 7.5, 1.0, 1.0 Hz), 5.60−5.49 (2H, m),
5.09−5.03 (4H, m), 2.76 (2H, dddd, J = 14.5, 7.5, 1.0, 1.0 Hz), 2.67
(2H, dddd, J = 14.0, 7.0, 1.0, 1.0 Hz); 13C NMR (100 MHz, CDCl3): δ
170.0, 151.8, 134.0, 130.9, 129.2, 127.1, 125.9, 121.7, 120.5, 88.4, 42.9.
3,3-Diallylhexahydroisobenzofuran-1(3H)-one (4b). Using the
standard acid anhydride double allylboration procedure and flash
chromatography on silica gel (15% EtOAc/hexanes) afforded 4.18
(0.110 g, 99%) as a clear oil. Rf = 0.50 (15% EtOAc/hexanes); IR (thin
film) νmax 3077, 2936, 2859, 1771, 1640, 1441, 1337, 1182, 1125, 976,
916 cm−1; 1H NMR (400 MHz, CDCl3): δ 5.86−5.71 (2H, m), 5.19−
5.10 (4H, m), 2.99 (1H, dd, J = 6.5, 6.5 Hz), 2.61−2.53 (2H, m),
2.37−2.31 (2H, m), 2.28−2.19 (2H, m), 1.81−1.72 (2H, m), 1.62−
1.52 (2H, m), 1.27−1.08 (4H, m); 13C NMR (100 MHz, CDCl3): δ
177.6, 132.5, 132.5, 119.6, 119.5, 86.9, 41.1, 39.8, 39.5, 37.5, 24.9, 23.9,
23.2, 22.8; LRMS (DART+) m/z (rel intensity) 238.2 (100) [M +
NH4]+, 221.2 (44) [M + H]+; HRMS (DART+) m/z calcd for
C14H21O2 [M + H]+: 221.1542. Found: 221.1545.
(3aR(S),4S(R),7R(S),7aS(R))-3,3-Diallyl-3a,4,7,7a-tetrahydro-4,7-
methanoisobenzofuran-1(3H)-one (4c). Using the standard acid
anhydride double allylboration procedure and flash chromatography
on silica gel (20% EtOAc/hexanes) afforded 4c (0.111 g, 96%) as a
clear oil. Rf = 0.53 (20% EtOAc/hexanes); IR (thin film) νmax 3076,
2982, 1750, 1641, 1336, 1328, 1205, 1145, 1016, 1000, 964, 920, 828
cm−1; 1H NMR (400 MHz, CDCl3): δ 6.24−6.19 (2H, m), 5.88 (1H,
dddd, J = 17.0, 10.5, 8.0, 6.0 Hz), 5.24 (1H, dddd, J = 17.5, 10.5, 7.5,
7.5 Hz), 5.22−5.13 (4H, m), 3.27−3.25 (1H, m), 3.05−3.03 (1H, m),
2.74−2.72 (1H, m), 2.63 (1H, dddd, J = 14.5, 6.0, 1.5, 1.5 Hz), 2.46−
2.39 (2H, m), 2.30 (1H, dddd, J = 14.0, 7.0, 1.0, 1.0 Hz), 2.20 (1H, d, J
= 8.0 Hz), 1.50−1.48 (2H, m); 13C NMR (100 MHz, CDCl3): δ
177.4, 139.1, 138.1, 132.7, 131.5, 121.0, 119.6, 86.7, 50.4, 49.5, 46.1,
45.4, 44.8, 44.0, 39.3; LRMS (DART+) m/z (rel intensity) 248.2 (93)
[M + NH4]+, 231.1 (100) [M + H]+; HRMS (DART+) m/z calcd for
C15H19O2 [M + H]+: 231.1385. Found: 231.1394.
4-Phenethylhepta-1,6-dien-4-amine (2m). Using the standard
nitrile double allylboration procedure and flash chromatography on
silica gel (15% MeOH/EtOAc + 0.5% NEt3) afforded 2m (0.053 g,
48%) as a yellow oil. Rf = 0.38 (15% MeOH/EtOAc); IR (thin film)
νmax 3360, 3187, 3074, 3026, 3002, 2927, 2860, 1638, 1603, 1496,
1456, 998, 915, 847, 824, 746, 699 cm−1; 1H NMR (400 MHz,
CDCl3): δ 7.30−7.25 (2H, m), 7.19−7.15 (3H, m), 5.92−5.82 (2H,
dddd, J = 16.0, 11.0, 7.5, 7.5 Hz), 5.17−5.12 (4H, m), 2.68−2.63 (2H,
m), 2.23−2.21 (4H, m), 1.90 (2H, br s), 1.69−1.65 (2H, m); 13C
NMR (100 MHz, CDCl3): δ 142.7, 133.8, 128.6, 128.5, 126.0, 119.0,
54.2, 44.6, 42.1, 30.2; LRMS (DART+) m/z (rel intensity) 216.2 (100)
[M + H]+; HRMS (DART+) m/z calcd for C15H22N [M + H]+:
216.1752. Found: 216.1759.
4-((1H-Indol-2-yl)methyl)hepta-1,6-dien-4-amine (2n). Using the
standard nitrile double allylboration procedure and flash chromatog-
raphy on silica gel (20% MeOH/EtOAc + 0.5% NEt3) afforded 2n
(0.078 g, 65%) as a light brown solid. Mp 78−80 °C (CDCl3); Rf =
0.33 (20% MeOH/EtOAc); IR (thin film in CDCl3) νmax 3409, 3334,
3164, 3063, 2976, 2919, 2849, 1640, 1576, 1458, 1439, 1365, 1340,
1234, 1109, 997, 915, 742 cm−1; 1H NMR (400 MHz, CDCl3): δ 8.31
(1H, br s), 7.63 (1H, d, J = 8.0 Hz), 2.20−2.02 (4H, m), 7.36 (1H, d, J
= 8.0 Hz), 7.18 (1H, ddd, J = 7.0, 7.0, 1.0 Hz), 7.13−7.10 (1H, m),
7.08 (1H, d, J = 2.0 Hz), 5.94 (2H, dddd, J = 17.5, 10.0, 7.5, 7.5 Hz),
5.17−5.08 (4H, m), 2.87 (2H, s), 2.29−2.24 (2H, m); 13C NMR (100
MHz, CDCl3): δ 136.2, 134.4, 128.9, 123.9, 122.1, 119.7, 119.6, 118.8,
111.6, 111.3, 54.9, 44.4, 35.8; LRMS (ESI+) m/z (rel intensity) 241.2
(24) [M + H]+, 224.1 (100), 130.1 (69); HRMS (ESI+) m/z calcd for
C16H21N2 [M + H]+: 241.1699. Found: 241.1695.
4-(Pyridin-4-yl)hepta-1,6-dien-4-amine (2o). Using the standard
nitrile double allylboration procedure and flash chromatography on
silica gel (10% MeOH/EtOAc) afforded 2o (0.085 g, 85%) as a yellow
oil. Rf = 0.30 (10% MeOH/EtOAc); IR (thin film) νmax 3366, 3287,
3076, 2978, 2925, 2855, 1691, 1641, 1597, 1553, 1441, 1410, 1070,
1
995, 919, 822, 566 cm−1; H NMR (400 MHz, CDCl3): δ 8.56−8.55
(2H, m), 7.36−7.35 (2H, m), 5.49 (2H, dddd, J = 17.0, 10.5, 8.5, 6.5
Hz), 5.10−5.06 (4H, m), 2.62 (2H, dddd, J = 14.0, 6.5, 1.5, 1.5 Hz),
2.44−2.38 (2H, m), 1.94 (2H, br s); 13C NMR (100 MHz, CDCl3): δ
156.1, 149.8, 132.9, 121.5, 119.8, 57.1, 47.7; LRMS (DART+) m/z (rel
intensity) 189.1 (100) [M + H]+; HRMS (DART+) m/z calcd for
C12H17N2 [M + H]+: 189.1392. Found: 189.1389.
(3aS(R),4S(R),7R(S),7aR(S))-3,3-Diallyl-3a,4,7,7a-tetrahydro-4,7-
methanoisobenzofuran-1(3H)-one (4d). Using the standard acid
anhydride double allylboration procedure and flash chromatography
on silica gel (30% EtOAc/hexanes) afforded 4d (0.117 g, 99%) as a
clear oil. Rf = 0.35 (20% EtOAc/hexanes); IR (thin film) νmax 3076,
2979, 2944, 2871, 1767, 1641, 1436, 1338, 1201, 1129, 998, 918, 812,
721 cm−1; 1H NMR (400 MHz, CDCl3): δ 6.29−6.23 (2H, m), 5.89−
5.71 (2H, m), 5.21−5.15 (4H, m), 3.39 (1H, dd, J = 9.0, 5.0 Hz),
3.25−3.22 (1H, m), 3.13−3.09 (1H, m), 2.80 (1H, dd, J = 9.0, 3.5
Hz), 2.54−2.49 (1H, m), 2.38−2.33 (3H, m), 1.64 (1H, ddd, J = 8.5,
2.0, 2.0 Hz), 1.43−1.41 (1H, m); 13C NMR (100 MHz, CDCl3): δ
177.6, 136.5, 134.8, 120.7, 119.4, 87.1, 53.1, 49.9, 45.9, 45.4, 45.1, 40.3;
LRMS (DART+) m/z (rel intensity) 248.2 (86) [M + NH4]+, 231.1
4-Benzylhepta-1,6-dien-4-amine (2p). Using the standard nitrile
double allylboration procedure and flash chromatography on silica gel
(EtOAc + 0.5% NEt3) afforded 2p (0.035 g, 35%) as a light yellow oil.
Rf = 0.20 (EtOAc); IR (thin film) νmax 3364, 3291, 3074, 3028, 3003,
2976, 2922, 2853, 1640, 1603, 1589, 1495, 1452, 1441, 1414, 1082,
1032, 997, 914, 745, 704 cm−1; 1H NMR (400 MHz, CDCl3): δ 7.32−
7.28 (2H, m), 7.25−7.21 (3H, m), 5.92 (2H, dddd, J = 17.5, 10.0, 7.5,
7.5 Hz), 5.18−5.09 (4H, m), 2.69 (1H, s), 2.18 (2H, dddd, J = 14.0,
7.5, 1.0, 1.0 Hz), 2.09 (2H, dddd, J = 14.0, 7.5, 1.0, 1.0 Hz), 1.47 (2H,
br s); 13C NMR (100 MHz, CDCl3): δ 137.8, 134.3, 130.9, 128.3,
1220
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Note
(100) [M + H]+; HRMS (DART+) m/z calcd for C15H19O2 [M + H]+:
231.1385. Found: 231.1397.
(11) Kramer, G. W.; Brown, H. C. J. Org. Chem. 1977, 42, 2292−
2299.
(12) (a) Bubnov, Y. N.; Mikhailov, B. M. Bull. Acad. Sci. USSR, Div.
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42, 4732−4739. (b) Gravel, M.; Lachance, H.; Lu, X.; Hall, D. G.
Synthesis 2004, 1290−1302. (c) Hall, D. G. Synlett 2007, 1644−1655.
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T. G.; Hall, D. G. Synthesis 2010, 893−907. (f) Elford, T. G.; Hall, D.
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ASSOCIATED CONTENT
■
S
* Supporting Information
NMR spectral images. This material is available free of charge
via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: rbatey@chem.utoronto.ca.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(14) For a review on the addition of organoboron reagents to imines,
see: Ramadhar, T. R.; Batey, R. A. Synthesis 2011, 1321−1346.
(15) For reviews of organotrifluoroborates, see: (a) Molander, G. A.;
Ellis, N. Acc. Chem. Res. 2007, 40, 275−286. (b) Stefani, H. A.; Cella,
R.; Vieira, A. S. Tetrahedron 2007, 63, 3623−3658. (c) Darses, S.;
We are grateful for financial support through the Natural
Science and Engineering Research Council (NSERC) of
Canada via a Discovery Grant for R.A.B., an Alexander Graham
Bell Canada Graduate Scholarship (CGS) D3 and CGS M for
T.R.R., and an Undergraduate Student Research Award
(USRA) for J.B. We also thank Dr. Farhad Nowrouzi and
Mr. John Janetzko for helpful discussions.
̂
Genet, J.-P. Chem. Rev. 2008, 108, 288−325.
(16) (a) Batey, R. A.; Thadani, A. N.; Smil, D. V. Tetrahedron Lett.
1999, 40, 4289−4292. (b) Batey, R. A.; Thadani, A. N.; Smil, D. V.;
Lough, A. J. Synthesis 2000, 990−998. (c) Thadani, A. N.; Batey, R. A.
Org. Lett. 2002, 4, 3827−3830. (d) Thadani, A. N.; Batey, R. A.
Tetrahedron Lett. 2003, 44, 8051−8055. (e) Nowrouzi, F.; Thadani, A.
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(17) Li, S.-W.; Batey, R. A. Chem. Commun. 2004, 1382−1383.
(18) Nowrouzi, F.; Batey, R. A. Angew. Chem., Int. Ed. 2013, 52, 892
−895.
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