Rhodium-catalyzed reaction of 2 h -azirines with carbonyl-ene-yne compounds giving 1-furyl-2-aza-1,3-dienes

Article abstract of DOI:10.1055/s-0033-1339190

A rhodium(II)-catalyzed reaction of carbonyl-ene-yne compounds, which are used as furylcarbene precursors, with 2H-azirines gave 1-furyl-2-aza-1,3-dienes as products. We propose that the title compounds are formed by the addition of furylcarbene-rhodium(I

Full text of DOI:10.1055/s-0033-1339190

LETTER
▌1541
lRetther odium-Catalyzed Reaction of 2H-Azirines with Carbonyl-ene-yne Com-
pounds Giving 1-Furyl-2-aza-1,3-dienes
Synthesis of 1-Furyl-2-aza-1,3-dienes
Kazuhiro Okamoto,* Masahito Watanabe, Ayano Mashida, Koji Miki, Kouichi Ohe*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510,
Japan
Fax +81(75)3832499; E-mail: kokamoto@scl.kyoto-u.ac.jp; E-mail: ohe@scl.kyoto-u.ac.jp
Received: 17.03.2013; Accepted after revision: 14.05.2013
transition-metal precursors led to lower yield of the prod-
Abstract: A rhodium(II)-catalyzed reaction of carbonyl-ene-yne
uct 3am.
compounds, which are used as furylcarbene precursors, with
2H-azirines gave 1-furyl-2-aza-1,3-dienes as products. We propose
that the title compounds are formed by the addition of furylcarbene–
rhodium(II) complexes to 2H-azirines followed by opening of
Table 1 Rhodium-Catalyzed Cyclopropanation of Alkenes via a
Thienylcarbene Complexa
2H-azirine rings.
Ph
O
Key words: alkynes, rhodium, carbenes, azirines, ring-opening re-
action
Ph
Rh2(OAc)4
(2.5 mol%)
N
O
Ph
+
N
Ph
Ph
CH2Cl2, r.t., 2 h
Me
2m Y mmol
Ph
2H-Azirines are the smallest nitrogen-containing unsatu-
rated heterocycles and have a C=N bond in their three-
membered ring. Owing to their high strain energy
(ca. 48 kcal/mol), a number of ring-opening reactions that
employ strain release as a driving force have been exten-
sively studied.1 Whereas thermal or photochemical trans-
formation of 2H-azirines is generally difficult to control,
2H-azirines act as vinylnitrene equivalents selectively in
transition-metal-catalyzed intramolecular cyclization,
leading to nitrogen-containing heterocyclic compounds.2–6
Me
1a X mmol
3am
Entry
X (mmol) Y (mmol) Catalyst
Yield (%)b
1
2
3
4
5
6
7
8
9
0.10
0.10
0.10
0.20
0.10
0.10
0.10
0.10
0.10
0.15
0.15
0.15
0.10
0.30
0.50
0.50
0.50
0.50
Rh2(OAc)4
45
20
2
Rh2(OCOCF3)4
Rh2(OCOCPh3)4
Rh2(OAc)4
33
62
73
36
43
47
Rh2(OAc)4
We have developed a variety of carbene-transfer reactions
involving carbene complexes generated by the activation
of alkynes with transition metals.7,8 This type of carbene
complex readily reacts with heteroaromatic compounds
such as furans and thiophenes to yield addition/ring-open-
ing reaction products efficiently.8c,9 During our concur-
rent study on the nickel-catalyzed disproportional
Rh2(OAc)4
[RhCl(cod)]2
[RuCl2(CO)3]2
[PtCl2(C2H4)]2
reaction of 2H-azirines,10 we found a rhodium-catalyzed a Reaction conditions: 1a (X mmol), 2m (Y mmol), and Rh2(OAc)4
(2.5 μmol), CH2Cl2 (1.5 mL).
reaction of carbonyl-ene-yne compounds with 2H-
b The yields were determined by 1H NMR analysis using nitrometh-
azirines giving 1-furyl-2-aza-1,3-dienes.11
ane as internal standard.
First, we employed Rh2(OAc)4 as a catalyst precursor ac-
cording to the previously reported carbene-transfer reac-
Table 2 summarizes the scope of the reaction with respect
to 2H-azirines.12 Another 2,2,3-trisubstituted azirine 2n
also reacted under the optimized conditions to give aza-
diene 3an13 in 80% isolated yield. The reaction of 2,3-di-
aryl-substituted 2H-azirines gave the corresponding
azadienes as single stereoisomers in high yields (71–86%,
entries 3–6). In the case of 2-methyl-3-phenyl-2H-azirine,
however, the ring-opening reaction product 3as was ob-
tained in only 37% yield, which could be due to the faster
formation of a dimer of 1a [(E)-1,2-difurylethylene; entry
7].
tions using carbonyl-ene-yne compounds. The reaction of
carbonyl-ene-yne 1a with azirine 2m proceeded well, and
the corresponding azadiene 3am was obtained in 45%
yield (Table 1, entry 1). Although rhodium trifluoroace-
tate and rhodium triphenylacetate are known to be more
active in some catalytic carbene-transfer reactions, they
were not effective (entries 2 and 3). The yield of 3am was
improved to 73% by using an excess of azirine 2m, which
may have suppressed the fast decomposition of carbonyl-
ene-yne 1a. The use of a rhodium(I) precursor or other
The scope of carbonyl-ene-yne compounds 1 is summa-
rized in Table 3. Aromatic substituents such as 4-methoxy,
4-chloro, and 2-methyl groups on the phenyl ketone moi-
ety were also available, and the yields of azadienes were
SYNLETT 2013, 24, 1541–1544
Advanced online publication: 11.06.2013
DOI: 10.1055/s-0033-1339190; Art ID: ST-2013-U0241-L
© Georg Thieme Verlag Stuttgart · New York
0
9
3
6
-
5
2
1
4
1
4
3
7
-
2
0
9
6

1542
K. Okamoto et al.
LETTER
in the range of 57–80%. In addition to cyclohexane-fused Scheme 2). The formation of imine 4 was observed by 1H
carbonyl-ene-yne compounds, aliphatic substrate 1e also NMR analysis after the first reduction.17
reacted to give azadiene 3en with a simple furan ring. The
Table 3 Rhodium-Catalyzed Reaction of Carbonyl-ene-yne Com-
reaction of 2n with thiocarbamoyl-ene-yne compound 1f,
pounds 1 with 2H-Azirine 2na
which is also used as a highly reactive carbene precur-
sor,8c afforded the corresponding thiophene-substituted
Ar
product, albeit in low yield (20%).
Ar
X
Rh2(OAc)4
(2.5 mol%)
N
Table 2 Rhodium-Catalyzed Reaction of Carbonyl-ene-yne 1a with
2H-Azirines 2a
X
Me
N
Me
Me
+
Ph
CH2Cl2, r.t., 2 h
Me
Ph
Ph
1
2n
3
O
Ph
Rh2(OAc)4
(2.5 mol%)
Entry Carbonyl-ene-yne 1
Azadiene 3
Yield (%)b
N
O
R2
N
R2
R3
+
CH2Cl2, r.t., 2 h
R1
Ar
O
Ar
O
R3
R1
1a
2
3
Entry
2
R1
R2
R3
3
Yield
(%)b
N
Me
Me
Ph
1
2
3
4
5
6
7
2m
2n
2o
2p
2q
2r
Me
Ph
Ph
Ph
Ph
Me
H
3am 73
1a (Ar = Ph)
1
2
3
4
3an
3bn
3cn
3dn
80
65
80
57
Me
3an
3ao
3ap
3aq
3ar
3as
94 (80c)
84
1b (Ar = 4-MeOC6H4)
1c (Ar = 4-ClC6H4)
1d (Ar = 2-MeC6H4)
Ph
4-MeOC6H4
4-ClC6H4
Ph
Ph
H
86
Ph
Ph
H
81
Ph
O
O
4-ClC6H4
Me
H
71
5
49
N
Me
Me
2s
Ph
H
37
a Reaction conditions: carbonyl-ene-yne 1a (0.10 mmol), azirine 2
(0.50 mmol), Rh2(OAc)4 (2.5 mol%), 1,2-dichloroethane (1 mL).
b Determined by 1H NMR analysis using nitromethane as internal
standard.
Ph
1e
3en
NMe2
c Isolated yield.
NMe2
S
S
6
20c
N
Me
Me
On the basis of previously reported metal-catalyzed car-
bene addition reactions with 2H-azirines,7 a proposed cat-
alytic cycle for the reaction of 1a and 2n is depicted in
Scheme 1. According to the proposed cycle, the furylcar-
bene–rhodium complex B would be generated by nucleo-
philic attack of the carbonyl oxygen on the coordinated
alkyne in complex A. Next, the nitrogen atom on the
azirine would add to the carbene to give rhodium-contain-
ing azirinium ylide C,14 which would undergo opening of
the three-membered ring of the azirine moiety to afford
azadiene 3an with the regeneration of the dirhodium cat-
alyst.15
Ph
1f
3fn
a Reaction conditions: carbonyl-ene-yne 1 (0.10 mmol), azirine 2n
(0.50 mmol), Rh2(OAc)4 (2.5 mol%), 1,2-dichloroethane (1 mL).
b Isolated yield.
c Determined by 1H NMR analysis using nitromethane as internal
standard.
In conclusion, we have developed a rhodium-catalyzed
carbene-addition/ring-opening reaction of 2H-azirines by
using carbonyl-ene-yne-compounds as carbenoid precur-
sors. The resulting 1-furyl-2-aza-1,3-dienes are readily re-
duced to aliphatic amines with a furan moiety. Further
investigations of such ring-opening reactions of other
heterocyclic compounds are underway.
Finally, we attempted the derivatization of the produced
2-azadienes. Although the Diels–Alder reactions using 2-
azadienes as diene units are well-known transformation
methods,16 to the best of our knowledge, hydride reduc-
tion of 2-azadienes to imines or amines has not been re-
ported. The two-step reduction of azadiene 3an with
LiAlH4 in Et2O at 40 °C followed by hydrolysis gave sec-
ondary amine 5 in good yield (70% for the two steps;
Synlett 2013, 24, 1541–1544
© Georg Thieme Verlag Stuttgart · New York

LETTER
Synthesis of 1-Furyl-2-aza-1,3-dienes
1543
III; Elsevier, Ltd: Amsterdam, 2008, 1–104. (e) Khlebnikov,
A. F.; Novikov, M. S. Tetrahedron 2013, 69, 3363.
(2) (a) Isomura, K.; Uto, K.; Taniguchi, H. J. Chem. Soc., Chem.
Commun. 1977, 664. (b) Chiba, S.; Hattori, G.; Narasaka, K.
Chem. Lett. 2007, 36, 52. (c) Jana, S.; Clements, M. D.;
Sharp, B. K.; Zheng, N. Org. Lett. 2010, 12, 3736.
(3) (a) Alper, H.; Prickett, J. E.; Wollowitz, S. J. Am. Chem.
Soc. 1977, 99, 4330. (b) Izumi, T.; Alper, H.
Ph
Ph
O
O
N
Me
Me
3an
Ph
[Rh]
1a
Organometallics 1982, 1, 322. (c) Auricchino, S.; Bini, A.;
Pastornerlo, E.; Truscello, A. M. Tetrahedron 1997, 53,
10911.
Ph
O
(4) (a) Alper, H.; Wollowitz, S. J. Am. Chem. Soc. 1975, 97,
3541. (b) Hayashi, K.; Isomura, K.; Taniguchi, H. Chem.
Lett. 1975, 1011. (c) Alper, H.; Prickett, J. E. J. Chem. Soc.,
Chem. Commun. 1976, 983.
Ph
Me
Me
O
N
C
(5) (a) Sakakibara, T.; Alper, H. J. Chem. Soc., Chem. Commun.
1979, 458. (b) Alper, H.; Perera, C. P. J. Am. Chem. Soc.
1981, 103, 1289. (c) Alper, H.; Perera, C. P.
[Rh]
Ph
Ph
A
[Rh]
O
Organometallics 1982, 1, 70.
(6) (a) Inada, A.; Hefmgartner, H. Helv. Chim. Acta 1982, 65,
1489. (b) Reddy, N. P.; Uchimaru, Y.; Lautenschlager, H.-
J.; Tanaka, M. Chem. Lett. 1992, 45. (c) Auricchino, S.;
Grassi, S.; Malpezzi, L.; Sartori, A. S.; Truscello, A. M. Eur.
J. Org. Chem. 2001, 1183. (d) Padwa, A.; Stengel, T.
Tetrahedron Lett. 2004, 45, 5991. (e) Candito, D. A.;
Lautens, M. Org. Lett. 2010, 12, 3312.
(7) For reviews, see: (a) Miki, K.; Uemura, S.; Ohe, K. Chem.
Lett. 2005, 34, 1068. (b) Kusama, H.; Iwasawa, N. Chem.
Lett. 2006, 35, 1082. (c) Ohe, K. Bull. Korean Chem. Soc.
2007, 28, 2153. (d) Ohe, K.; Miki, K. J. Synth. Org. Chem.,
Jpn. 2009, 67, 1161.
[Rh]
[Rh]
N
Me
Me
Ph
O
Ph
2n
B
Scheme 1 A proposed catalytic cycle for the rhodium-catalyzed re-
action of carbonyl-ene-yne 1a with azirine 2n
(8) (a) Miki, K.; Nishino, F.; Ohe, K.; Uemura, S. J. Am. Chem.
Soc. 2002, 124, 5260. (b) Nishino, F.; Miki, K.; Kato, Y.;
Ohe, K.; Uemura, S. Org. Lett. 2003, 15, 2615.
(c) Tsuneishi, A.; Okamoto, K.; Ikeda, Y.; Murai, M.; Miki,
K.; Ohe, K. Synlett 2011, 655.
(9) (a) Miki, K.; Fujita, M.; Kato, Y.; Uemura, S.; Ohe, K. Org.
Lett. 2006, 8, 1741. (b) Ikeda, Y.; Murai, M.; Abo, T.; Miki,
K.; Ohe, K. Tetrahedron Lett. 2007, 48, 6651.
Ph
O
Ph
O
1) LiAlH4
THF, 40 °C
2) H2O
N
Me
Me
N
Me
Me
4
3an
Ph
Ph
(10) We have reported a nickel-catalyzed disproportionation of
2H-azirines giving 2-aza-1,3-dienes and nitriles, see:
Okamoto, K.; Mashida, A.; Watanabe, M.; Ohe, K. Chem.
Commun. 2012, 48, 3554.
Ph
O
1) LiAlH4
THF, 40 °C
(11) A few stoichiometric or catalytic reactions of 2H-azirines
with carbene complexes were reported. See: (a) Hegedus, L.
S.; Kramer, A.; Yijun, C. Organometallics 1985, 4, 1747.
(b) Khlebnikov, A. F.; Novikov, M. S.; Amer, A. A.
Tetrahedron Lett. 2004, 45, 6003. (c) Khlebnikov, A. F.;
Amer, A. A.; Kostikov, R. R.; Magull, J.; Vidovic, D. Russ.
J. Org. Chem. 2006, 42, 515. (d) Loy, N. S. Y.; Singh, A.;
Xu, X.; Park, C.-M. Angew. Chem. Int. Ed. 2013, 52, 2212.
(12) General procedure for the catalytic reactions: A solution
of [Rh2(OAc)4] (1.1 mg, 2.5 μmol), carbonyl-ene-yne 1
(21.0 mg, 0.10 mmol), and azirine 2 (0.50 mmol) in CH2Cl2
(1.0 mL) was stirred at r.t. for 2 h. The reaction mixture was
filtered through a pad of Florisil with EtOAc, and the solvent
was removed under reduced pressure. The yield of azadiene
3 was estimated by 1H NMR analysis of the crude product
with nitromethane (0.10 mmol, 5.4 μL) as internal standard.
The remaining azirine 2 was distilled off by Kugelrohr
distillation. The residue was passed through a pad of Florisil
to give azadiene 3.
2) H2O
NH
Ph
Me
Me
5: 70%
(for 2 steps)
Scheme 2 Transformation of azadiene 3an into amine 5
Acknowledgment
This work was financially supported by a Grant-in-Aid for Scienti-
fic Research (B) (Grant No. 22350087) from MEXT, Japan.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.SnoIufproig
m
iotSrat
ungIifoop
r
t
References and Notes
Azadiene 3an: Yield: 28.3 mg (0.080 mmol, 80%); pale-
orange oil. 1H NMR (CDCl3): δ = 1.67 (s, 3 H), 1.71–1.82
(m, 4 H), 2.25 (s, 3 H), 2.74–2.90 (m, 4 H), 7.11 (d,
J = 6.8 Hz, 2 H), 7.22 (t, J = 7.3 Hz, 1 H), 7.34 (t,
J = 6.8 Hz, 1 H), 7.36 (t, J = 7.3 Hz, 2 H), 7.42 (t,
(1) For reviews, see: (a) Anderson, D. J.; Hassner, A. Synthesis
1975, 483. (b) Gilchrist, T. L. Aldrichimica Acta 2001, 34,
51. (c) Palacios, F.; de Retana, A. M. O.; de Marigorta, E.
M.; de los Santos, J. M. Eur. J. Org. Chem. 2001, 2401.
(d) Padwa, A. In Comprehensive Heterocyclic Chemistry
© Georg Thieme Verlag Stuttgart · New York
Synlett 2013, 24, 1541–1544

1544
K. Okamoto et al.
LETTER
J = 7.3 Hz, 2 H), 7.55 (s, 1 H), 7.65 (d, J = 7.3 Hz, 2 H). 13
C
Ph
O
NMR (CDCl3): δ = 19.4, 21.8, 22.4, 22.5, 22.9, 23.1, 121.3,
124.7, 126.8, 127.1, 128.1, 128.4, 128.5, 130.2, 131.1,
132.8, 137.0, 144.3, 144.8, 146.5, 148.3. HRMS (FAB): m/z
[M + H]+ calcd for C25H26NO: 356.2014; found: 356.2014.
Azadiene 3bn: Yield: 24.9 mg (0.065 mmol, 65%); pale-
yellow oil. 1H NMR (CDCl3): δ = 1.66 (s, 3 H), 1.68–1.85
(m, 4 H), 2.25 (s, 3 H), 2.65–2.89 (m, 4 H), 3.82 (s, 3 H),
6.90 (d, J = 8.8 Hz, 2 H), 7.11 (d, J = 7.3 Hz, 2 H), 7.34 (t,
J = 7.8 Hz, 1 H), 7.42 (t, J = 7.3 Hz, 2 H), 7.53 (s, 1 H), 7.59
(d, J = 8.8 Hz, 2 H). 13C NMR (CDCl3): δ = 21.8, 22.5, 22.5,
22.8, 23.2, 55.3, 114.0, 119.7, 124.4, 126.3, 127.1, 128.4,
130.3, 132.3, 137.2, 144.2, 144.8, 145.9, 148.6, 158.7.
HRMS (FAB): m/z [M + H]+ calcd for C26H28NO2:
386.2120; found: 386.2115.Azadiene 3cn: Yield: 31.3 mg
(0.080 mmol, 80%); pale-yellow oil. 1H NMR (CDCl3): δ =
1.67 (s, 3 H), 1.70–1.85 (m, 4 H), 2.25 (s, 3 H), 2.70–2.90
(m, 4 H), 7.11 (d, J = 7.3 Hz, 2 H), 7.33 (t, J = 7.3 Hz, 2 H),
7.36 (t, J = 7.3 Hz, 1 H), 7.42 (t, J = 7.3 Hz, 2 H), 7.53 (s,
1 H), 7.57 (d, J = 8.8 Hz, 2 H). 13C NMR (CDCl3): δ = 19.4,
21.9, 22.4, 22.5, 22.9, 23.1, 121.8, 125.9, 127.2, 128.1,
128.6, 128.7, 129.8, 130.3, 132.5, 133.3, 137.0, 144.1,
144.8, 146.7, 147.3. HRMS (FAB): m/z [M + H]+ calcd for
C25H25ClNO: 390.1625; found: 390.1637.
Me
Me
N
3an
H
H
8% NOE
Figure 1 Geometry of azadiene 3ar
(14) Fragmentation from metal-free azirinium ylide or a
metallacycle generated by the insertion of B into the C–N
single bond of 2n could be an alternative route to the 2-
azadiene.
(15) The reason for stereoselective formation of 3ao–3ar may be
that the transition state from C settles into the conformation
with the least steric hindrance.
(16) (a) Dehnel, A.; Finet, J. P.; Lavielle, G. Synthesis 1977, 474.
(b) Palacios, F.; Alonso, C.; Rubiales, G. J. Org. Chem.
1997, 62, 1146. (c) Jayakumar, S.; Ishar, M. P. S.; Mahajan,
M. P. Tetrahedron 2002, 58, 379.
(17) Reduction of azadiene 3an: To a solution of azadiene 3an
(35.5 mg, 0.10 mmol) in THF (1.0 mL) was added LiAlH4
(19.0 mg, 0.50 mmol) in one portion, and the reaction
mixture was stirred at 40 °C for 2 h. The reaction was
quenched with 1.0 M aq NaOH, and extracted with EtOAc.
The organic layer was dried over Na2SO4, filtered, and
concentrated under vacuum to give a crude product imine 4.
The residue was used in the next reduction without further
purification. The second reduction of imine 4 was performed
under the same conditions as the first reduction of azadiene
3an. The crude mixture was subjected to column
chromatography on silica gel (hexane–EtOAc, 10:1) to give
amine 5.
Azadiene 3dn: Yield: 21.0 mg (0.057 mmol, 57%); pale-
orange oil. 1H NMR (CDCl3): δ = 1.66 (s, 3 H), 1.67–1.82
(m, 4 H), 2.23 (s, 3 H), 2.36 (s, 3 H), 2.54 (t, J = 5.9 Hz,
2 H), 2.88 (t, J = 6.3 Hz, 2 H), 7.09 (d, J = 7.8 Hz, 2 H),
7.15–7.22 (m, 3 H), 7.27–7.33 (m, 2 H), 7.39 (t, J = 7.3 Hz,
2 H), 7.53 (s, 1 H). 13C NMR (CDCl3): δ = 19.4, 20.8, 21.8,
22.2, 22.4, 22.8, 23.2, 122.0, 125.3, 127.0, 127.1, 128.0,
128.5, 129.0, 130.27, 130.31, 130.9, 132.6, 137.0, 137.1,
144.4, 144.8, 146.9, 149.9. HRMS (FAB): m/z [M + H]+
calcd for C26H28NO: 370.2171; found: 370.2183.
Azadiene 3en: Yield: 14.8 mg (0.049 mmol, 49%); pale-
orange oil. 1H NMR (CDCl3): δ = 1.68 (s, 3 H), 2.31 (s, 3 H),
6.72 (d, J = 3.4 Hz, 1 H), 6.79 (d, J = 3.4 Hz, 1 H), 7.12 (d,
J = 6.8 Hz, 2 H), 7.28 (t, J = 7.8 Hz, 1 H), 7.33–7.38 (m,
1 H), 7.39 (d, J = 6.3 Hz, 2 H), 7.42 (d, J = 7.3 Hz, 2 H),
7.45 (s, 1 H), 7.73 (d, J = 6.8 Hz, 2 H). 13C NMR (CDCl3): δ
= 19.3, 22.0, 107.4, 115.4, 124.3, 127.3, 128.0, 128.6, 128.7,
130.1, 130.3, 134.4, 137.0, 143.2, 144.2, 152.9, 155.7.
HRMS (FAB): m/z [M + H]+ calcd for C21H20NO: 302.1545;
found: 302.1536.
Imine 4: 1H NMR (CDCl3): δ = 1.11 (s, 3 H), 1.14 (s, 3 H),
1.60–1.80 (m, 4 H), 2.43 (t, J = 5.5 Hz, 2 H), 2.75 (t,
J = 5.9 Hz, 2 H), 2.85 (septet, J = 7.0 Hz, 1 H), 4.31 (s, 2 H),
7.12–7.40 (m, 6 H), 7.42 (t, J = 7.0 Hz, 2 H), 7.58 (d,
J = 7.0 Hz, 2 H).
Amine 5: Yield: 25.0 mg (0.070 mmol, 70%); pale-yellow
oil. 1H NMR (CDCl3): δ = 0.73 (d, J = 6.4 Hz, 3 H), 0.96 (d,
J = 6.8 Hz, 3 H), 1.60–1.79 (m, 4 H), 1.83 (br s, 1 H), 1.85
(octet, J = 6.8 Hz, 1 H), 2.17–2.35 (m, 2 H), 2.75 (t,
J = 6.4 Hz, 2 H), 3.33 (d, J = 7.3 Hz, 1 H), 3.45 (d,
J = 14.6 Hz, 1 H), 3.63 (d, J = 14.2 Hz, 1 H), 7.19 (t,
J = 7.3 Hz, 1 H), 7.23–7.35 (m, 5 H), 7.37 (t, J = 7.8 Hz,
2 H), 7.60 (d, J = 7.3 Hz, 2 H). 13C NMR (CDCl3): δ = 19.4,
19.6, 20.4, 22.8, 23.0, 23.4, 34.4, 42.4, 68.3, 118.9, 120.3,
124.1, 125.9, 126.8, 127.9, 128.3, 128.5, 132.2, 142.4,
145.4, 146.8. HRMS (FAB): m/z [M + H]+ calcd for
C25H30NO: 360.2327; found: 360.2324.
(13) Geometry of azadiene 3ar was determined by 1H NMR NOE
experiments, see Figure 1.
Synlett 2013, 24, 1541–1544
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