Gold catalysis: 1,3-Oxazines by cyclisation of allene amides

Article abstract of DOI:10.1002/chem.201100132

A series of allene amides was prepared and their gold-catalysed cyclisation was investigated. The formation of six-membered rings, 1,3-oxazines, was observed. Dihydropyrroles originating from intramolecular hydroamination of the distal C=C double bonds of

Full text of DOI:10.1002/chem.201100132

FULL PAPER
DOI: 10.1002/chem.201100132
Gold Catalysis: 1,3-Oxazines by Cyclisation of Allene Amides
A. Stephen K. Hashmi,*[a] Andreas M. Schuster,[a] Sebastian Litters,[a]
Frank Rominger,[a] and Markus Pernpointner[b]
Abstract: A series of allene amides was
31P NMR spectroscopy showed only
one additional species during the con-
version in each case; a computational
study of the different allyl gold(I) spe-
cies involved allowed this to be as-
prepared and their gold-catalysed cycli-
sation was investigated. The formation
of six-membered rings, 1,3-oxazines,
was observed. Dihydropyrroles origi-
nating from intramolecular hydroami-
nation of the distal C=C double bonds
of the allenes were minor side prod-
ucts. Mechanistic studies by in situ
signed as the s-allyl gold species bear-
ing the gold catalyst at the sterically
less hindered methylene end. The re-
giospecific deuterodeauration of this
intermediate confirmed
a
SE’-type
Keywords: allenes · gold · hetero-
mechanism for this last step of the cat-
alytic cycle.
cycles
· intermediates · labeling
studies · oxazines
Introduction
Gold is known to be a very effective catalyst for additions
of nucleophiles to carbon multiple bonds.[1] Allenes have
been used since 2000,[2] recently very successfully, especially
in the synthesis of heterocycles.[3] Of the numerous transi-
tion-metal-catalysed intramolecular additions to allenes,
only two examples that used an allenamide motive were
known previously (Scheme 1), and only silver(I) has been
used for catalytic conversions of these substrates.[4]
Scheme 2. Reaction patterns of intramolecular additions to allenes.
Scheme 1. The only two allene amide substrates previously used in transi-
tion-metal-catalysed intramolecular additions.
ing the central allene carbon atom in each case. This is quite
remarkable, because both silver[5] and gold,[6] as well as pal-
ladium,[7] normally catalyse 5-exo-trig cyclisation (path a).
Nucleophilic attack at the central allenic carbon atom has
only been observed in titanium-catalysed hydroamination.[8]
Path d has not yet been observed, but with a shorter tether
between the nucleophile and allene the distal carbon atom
of the allene has also been reported to participate in such a
gold-catalysed endo-trig cyclization.[9]
In continuation of our work on cyclisations of propargyla-
mides to oxazoles, methyleneoxazolines and oxazines,[10,11,12]
which have also been used in industry,[13] we were now inter-
ested in studying the reactivities of the corresponding alle-
nylamides.
Interestingly, in these two examples only 6-exo-dig cyclisa-
tion (Scheme 2, path b) or 6-endo-dig cyclisation (Scheme 2,
path c) were observed, with the nucleophilic oxygen attack-
[a] Prof. Dr. A. S. K. Hashmi, Dipl.-Chem. A. M. Schuster, S. Litters,
Dr. F. Rominger+
Organisch-Chemisches Institut
Ruprecht-Karls-Universitꢀt Heidelberg
Im Neuenheimer Feld 270, 69120 Heidelberg (Germany)
Fax : (+49)6221-544205
E-mail: hashmi@hashmi.de
[b] Dr. M. Pernpointner
Theoretische Chemie, Physikalisch-Chemisches Institut
Ruprecht-Karls-Universitꢀt Heidelberg
Im Neuenheimer Feld 229, 69120 Heidelberg (Germany)
[+] Crystallographic investigation
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100132.
Chem. Eur. J. 2011, 17, 5661 – 5667
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without
a prior cyclisation to the alkylideneoxazoline
(Scheme 3, path a).
To explore the scope of the reaction, different R groups
were investigated. The yields of the allenes and the vinylox-
azole side products are shown in Table 1 and are poor to
moderate, as is known for this method in general (although
it is still state-of-the-art).[16] With phenyl and styryl groups
(Table 1, entries 1 and 2) substantial amounts of the vinylox-
azoles 3a and 3b were obtained. The highest yields of 2
were obtained with furyl and dimethylfuryl substituents
(Table 1, entries 3 and 4), with only minor amounts of the
byproducts being observed. With nitrofuryl (entry 5), thio-
phenyl (entry 6) and adamantyl (entry 7) substituents, and
also with aliphatic substrates with ester groups (entries 8–
10), only low yields of 2 were obtained. For the thiophene-
based substrate an inhibiting interaction between the sulfur
atom and the copper catalyst can be assumed.
We could now investigate gold-catalysed conversions of
the substrates 2. To explore the conditions, we started with a
qualitative screening (Table 2). Without toluene sulfonic
acid (TsOH) the Ph3PAuCl/AgI combination gave no con-
version at all (Table 2, entry 1), whereas with TsOH[17] only
compound 4a and some 5a were obtained after 48 h
(entry 2). The gold catalyst was thus now initiating an attack
at the central position of the allene and not following the
usual 5-exo-trig path a from Scheme 2, which had seemed to
be intrinsic for this substrate class. Furthermore, compound
6a, the product of an intramolecular hydroamination of the
distal allene double bond to form a dihydropyrrole ring, was
also identified as an additional byproduct (compare also
Table 2, entries 5 and 6).
Scheme 3. Synthesis of the substrates 2 and the observed side products 3.
Results and Discussion
The substrates 2 were synthesised by the method of Crabbꢂ
et al.[5b,14] with use of an improved protocol developed by
Trost et al.[15] (Scheme 3). With some of the propargylamides
1, the vinyloxazoles 3 were obtained as side products
(Table 1). This new synthesis of these compounds probably
Table 1. Synthesis of the allenamides 2 and the side products 3 by the
method of Crabbꢂ et al.
Entry Starting
material
R
Product Yield Product Yield
[%]
[%]
1
1a
2a
34
3a
20
2
3
1b
1c
2b
2c
28
55
3b
3c
20
1
In continuation of the solvent and catalyst screening, tosy-
À
late, triflate and NTf2 counter ions were used with
Ph3PAu + cations in three different solvents. With tosylate in
dioxane, similarly to the case in dichloromethane, com-
pounds 4 and 5 were obtained (Table 2, entry 3). In metha-
nol the reaction failed (entry 4); this was also the case for
4
1d
2d
48
3d
4
À
the other two counter ions (entries 7 and 10). For NTf2 this
5
6
7
1e
1 f
1g
2e
2 f
2g
24
9
3e
3 f
3g
–
–
was also observed even in dioxane (Table 2, entry 9), al-
though this counter ion gave normal conversions in di-
chloromethane (entry 8). The palladium catalyst was com-
pletely inactive (entry 11).[18] Neither was any conversion
observed on testing AgNO3 in acetone (Table 2, entry 12),
in analogy to work by Brummond et al.[4] (compare
Scheme 1). If the catalyst was active, it always gave com-
plete conversions. The optimised conditions—Ph3PAuCl,
AgOTs and TsOH as the catalyst system in dichlorome-
thane—were used for the other substrates.
In subsequent quantitative experiments under the opti-
mised conditions, the 6-endo-dig pathway afforded 4a in
66% yield after complete conversion (Table 3, entry 1),
whereas after 24 h (incomplete conversion) a 53% yield of
4a and a 5% yield of the 6-exo-dig cyclisation product 5a
was obtained. No dihydrooxazole C was formed (Table 3,
entry 2). For this substrate the (IPr)AuCl precatalyst with an
NHC ligand (Scheme 4) was also tested; this catalyst
showed a significant change in the product distribution of
15
12
8
1h
1i
2h
2i
4
8
8
3h
3i
–
–
–
9
10
1j
2j
3j
proceeds via intermediates A and path b (Scheme 3). Under
the basic reaction conditions the allylamines B are formed
by cyclisation, and subsequent elimination of diisopropyla-
mine delivers the aromatic products 3. The allenes 2 evolve
from A through the direct elimination of diisopropylamine
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Chem. Eur. J. 2011, 17, 5661 – 5667

Gold Catalysis: 1,3-Oxazines by Cyclisation of Allene Amides
Table 2. Solvent and counter ion screening (reaction time 48 h).
FULL PAPER
To establish whether or not
interconversion of the products
4 and 5 by isomerisation is pos-
sible, compounds 4a and 5a
were each treated with gold cat-
alyst under the usual reaction
conditions from Table 3. Even
after one week no isomerisation
was observed, but only slow de-
composition (Figure 2). In the
next experiment we added D2O
to the reaction mixture. The
1H NMR spectrum taken in situ
shows deuteration exclusively
at only one position: the inte-
gral of the allylic position at
d=2.5 ppm (labelled 2 in the
spectrum) is reduced to only
one proton. A 13C NMR spec-
trum taken from the same solu-
tion (Figure 3) confirms this re-
gioselective deuteration of the
allylgold intermediate: only the
allylic carbon at d=26 ppm
Entry Catalyst
Solvent Product
1
2
3
4
5
6
7
Ph3PAuCl (5 mol%)/AgOTs (5 mol%)
CH2Cl2
CH2Cl2
no conversion
4a (byproduct 5a, traces of 6a)
Ph3PAuCl (5 mol%)/AgOTs (5 mol%) TsOH (5 mol%)
Ph3PAuCl (5 mol%)/AgOTs (5 mol%) TsOH (5 mol%)
Ph3PAuCl (5 mol%)/AgOTs (5 mol%) TsOH (5 mol%)
Ph3PAuCl (5 mol%)/AgOTf (5 mol%) TsOH (5 mol%)
Ph3PAuCl (5 mol%)/AgOTf (5 mol%) TsOH (5 mol%)
Ph3PAuCl (5 mol%)/AgOTf (5 mol%) TsOH (5 mol%)
dioxane 4a (byproduct 5a)
MeOH
CH2Cl2
dioxane 4a (traces of 6a)
MeOH
no conversion
4a (traces of 6a)
no conversion
4a (traces of 5a)
8
Ph3PAuCl (5 mol%)/AgNTf2 (5 mol%) TsOH (5 mol%) CH2Cl2
9
Ph3PAuCl (5 mol%)/AgNTf2 (5 mol%) TsOH (5 mol%) dioxane no conversion
Ph3PAuCl (5 mol%)/AgNTf2 (5 mol%) TsOH (5 mol%) MeOH no conversion
10
11
12[a]
[PdCl
G
dioxane no conversion
acetone no conversion
[b]
AgNO3
Reactions analysed by 1H NMR: [a] control experiments with AgOTs, AgOTf or AgNTf2 and TsOH gave no
conversion; [b] no TsOH was used, reaction carried out at 608C
4a and 6a (Table 3, entry 3),
with 6a becoming the main
product (45%) and 4a a side
product (25%). With a styryl
substituent (Table 3, entry 4)
only product 4b was obtained,
in poor yield. A furyl substitu-
ent gave an even lower yield of
4c (Table 3, entry 5) but a 23%
yield of 6c, whereas with 4d a
Scheme 4.
lyst.
ACHTUNGTRENNUNG(IPr)AuCl precata-
normal yield was obtained (Table 3, entry 6), again with ac-
companying 6d (23%). A nitrofuryl compound (Table 3,
entry 7) did not give any 6e but afforded 4e (53%) and 5e
(10%). The results with the thienyl substituent (Table 3,
entry 8) were similar to those in the dimethylfuryl case
(entry 6). The presence of an adamantyl substituent
(Table 3, entry 9) resulted only in 4g, whereas aliphatic sys-
tems with ester groups (Table 3, entries 10–12) showed no
conversion at all.
Figure 2. In situ 1H NMR spectra of 4a generated from a gold-catalysed
reaction in the presence of a large excess of D2O (top) and reference
spectrum of pure 4a (bottom).
Compound 6 f gave crystals suitable for an X-ray crystal
1
structure
analysis
from
dichloromethane/hexanes
shows the typical triplet for a JC,D coupling with deuterium
(Figure 1).[19] The structure provided unambiguous confirma-
indicating a chemoselective monodeuteration.
tion of the connectivity of 6.
In view of our recent work in isolating stable vinylgold in-
termediates from organic reactions,[11] we treated substrate
2a with (IPr)AuOTs catalyst (1 equiv) in the presence of
triethylamine (1.2 equiv) (Scheme 5).
No allylgold intermediate could be isolated, but com-
pounds 4a and 5a were formed in a 2:1 ratio. Use of
Gagnꢂꢃs protocol[20] with Ph3PAuOTs (1 equiv) and 1,5-di-
tert-butylpyridine (1.2 equiv) as a base exclusively yielded
4a as a single product. The latter reaction was monitored by
31P NMR spectroscopy at room temperature (Figure 4). The
Figure 1. Crystal structure of 6 f.
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5663

A. S. K. Hashmi et al.
Table 3. Catalytic conversion of allenamides.[a]
Entry
Starting
material
R
Time
Product
(yield [%])
AHCTUNGTRENNUNG
1
2a
2a
2a
2 d
1 d
2 d
4a (66)
4a (53)+
5a (5)
2[b]
4a (25)+
6a (45)
3[c]
4
5
2b
2c
3 d
3 d
4b (18)
4c (10)+
6c (23)
Scheme 5. Stoichiometric experiments: [a] with Et3N (1.2 equiv) as base,
[b] with 2,6-di-tert-butylpyridine (1.2 equiv) as base.
4d (38)+
6d (23)
6
2d
2 d
4e (53)+
5e (10)
7
8
9
2e
2 f
2g
3 d
3 d
3 d
4 f (35)+
6 f (23)
4g (43)
10
11
12
2h
2i
3 d
3 d
3 d
4h (–)
4i (–)
4j (–)
2j
[a] Standard reaction conditions with Ph3PAuCl (5 mol%), AgOTs
(5 mol%) and TsOH (5 mol%) as the catalyst system in dichlorome-
thane at 608C. [b] Reaction time 24 h at RT, incomplete conversion.
[c] (IPr)AuCl instead of Ph3PAuCl.
Figure 4. 31P NMR spectra of Ph3PAuOTs (top), Ph3PAuOTs+2a after
4 h (middle) and Ph3PAuOTs+2a after 30 min (bottom).
free catalyst shows a signal at d=32.66 ppm, whereas during
the reaction a new signal appeared at 46.08 ppm. Only 4a
was obtained as a product under these conditions and one
intermediate was observed in the 31P NMR spectrum, so the
signal at d=46.08 ppm must belong to the thermodynami-
cally more stable intermediate.
To determine which of the isomeric intermediates D or E
is more stable, we conducted a computational study relating
to the relative thermodynamic stabilities of the two species.
For the characterization of the two structures D and E and
a possible third intermediate, the p-allyl complex F, we per-
formed density functional theory (DFT) calculations using
the B3LYP functional[21] together with a cc-pVDZ basis[22]
on all atoms. For gold, a relativistic effective core potential
(RECP) from reference [23] was also employed, to account
for relativistic effects. Computations based on effective core
potentials lead to considerable reductions in electron num-
bers and maintain the same accuracy as corresponding all-
electron calculations. Additionally, the phenyl groups on
phosphorus were replaced by methyl groups, which did not
Figure 3. In situ 13C NMR spectra of 4a generated from a gold-catalysed
reaction in the presence of a large excess of D2O (top) and reference
spectrum of pure 4a (bottom).
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Gold Catalysis: 1,3-Oxazines by Cyclisation of Allene Amides
FULL PAPER
lead to distortions of the overall picture. All calculations
were performed with the Gaussian 03 program package.[24]
Geometry optimizations were performed for the two struc-
tures D and E (Figure 5), clearly indicating two stable
minima possessing ground state energies of À1152.1140 a.u.
(D) and À1152.1201 a.u. (E), the latter slightly stabilized by
These findings, E being the intermediate observed in the
in situ NMR studies at room temperature and the deuterium
electrophile entering exclusively at the position in the ring
(labelled 2 in Figure 2 and Figure 3) show that the proto-
deauration in this s-allyl gold(I) species occurs by a SE’
pathway.
3.86 kcalmolÀ1. The corresponding Au C bond lengths
À
Conclusion
These results show that the allenamides 2 in gold-catalysed
reactions mainly lead to 1,3-oxazines, sometimes accompa-
nied by the N-acylpyrrolines 5. The detection of the inter-
mediate by in situ 31P NMR spectroscopy, labelling experi-
ments and an accompanying computational study clearly es-
tablish the reaction pathway, via the intermediate E and an
SE’-type protodeauration. This is of general importance for
conversions of such s-allyl gold(I) species.
Experimental Section
Figure 5. The p-allyl species F (middle) is the transition state of the inter-
conversion of species D (left) and E (right).
General methods: Chemicals (Aldrich, Fluka, Lancaster and Merck)
were used without further purification. Diethyl ether and tetrahydrofuran
were dried over sodium. NMR spectra were recorded with Bruker
ARX 500, ARX 300 and AMX 250 spectrometers. Chemical shifts were
referenced to residual solvent protons. Signal multiplicity as follows: s
(singlet), d (doublet), t (triplet), q (quartet), m (multiplet). 13C assign-
ment was achieved through DEPT 90 and DEPT 135 spectra. MS spectra
were recorded with a Finnigan MAT 90, a Varian 711 or a micrOTOF-Q
spectrometer. IR spectra were recorded with a Bruker Vector 22 instru-
ment.
amount to 2.118 ꢄ (12a) and 2.102 ꢄ (E) and it might be
asked whether a third stable p-allylic conformation such as
F exists. Starting directly with a predecessor of F led to a
structure possessing two imaginary frequencies not qualify-
ing either as a transition state or as a stable minimum. How-
ever, one of the imaginary frequencies reflected a nuclear
motion in which the carbon atoms C1 and C3 mutually
moved toward the gold atomic centre, indicating a shift of
the gold centre from atom C1 to C3. During this motion the
corresponding opposite gold/carbon bond lengths are notice-
ably elongated. It is therefore unlikely that structure F
could represent a stable minimum and the intermediate re-
sults point more to a (still insufficiently characterized) tran-
sition state. For an exact determination of the character of
structure F we performed a transition-state search based on
the quadratic synchronous transit (QST2).[25] Here the opti-
mized educt and product structures are provided to the
search algorithm that optimizes connecting structures under
the constraint of one imaginary frequency. To achieve opti-
mal convergence the force constants were recalculated in
each step. This procedure led to the converged transition-
state structure F, with one imaginary frequency representing
the same motion of the carbon backbone as described above
for the directly optimized structure. The three Au–C distan-
ces amount to 2.437 ꢄ (C1), 2.317 ꢄ (C2) and 2.425 ꢄ (C3),
together with a total electronic energy of À1152.0721 a.u.
We therefore conclude that the Au–C s-bound structures D
and E are the only stable species and that a proposed p-al-
lylic complex does not represent a minimum but a true tran-
sition state that leads to an activation barrier of +26.3 kcal
molÀ1 for the isomerization (see Figure 5).[26]
Compounds 1a–1j are known and fully characterized.[10, 12]
General Procedure 1 (GP1):[15] A propargylamide (1 equiv), paraformal-
dehyde (2 equiv), diisopropylamine (2 equiv) and copper(I) bromide
(0.3 equiv) were dissolved in 1,4-dioxane in a 50 mL round-bottomed
flask. The reaction mixture was heated for 10 h at 1008C. Workup was
carried out by column chromatography on silica with petroleum ether
(PE) and ethyl acetate (EA) as eluents.
General Procedure 2 (GP2): The substrate (1 equiv) and Ph3PAuCl
(5 mol%), AgOTs (5 mol%) and TsOH·H2O (5 mol%) were dissolved
in dry CH2Cl2 (2 mL) in a 12 mL sealed reaction tube. The reaction mix-
ture was heated for the indicated amount of time at 608C. Workup was
carried out by column chromatography on silica with PE and EA as elu-
ents.
N-(Buta-2,3-dien-1-yl)benzamide (2a) and 2-phenyl-5-vinyl-1,3-oxazole
(3a): N-(Prop-2-yn-1-yl)benzamide (1a, 2.00 g, 12.6 mmol), paraformalde-
hyde (760 mg, 25.2 mmol), diisopropylamine (2.55 g, 25.2 mmol) and cop-
per(I) bromide (600 mg, 4.20 mmol) were used as described in GP1.
Column chromatography (PE/EA 4:1) yielded 2a (737 mg, 34%, Rf =
0.26) as a slightly brown solid and 3a
(426 mg, 20%, Rf =0.49) as a yellow
oil.
Compound 2a: 1H NMR (300 MHz,
CDCl3): d=3.95–4.03 (m, 2H), 4.79–
4.87 (m, 2H), 5.22–5.33 (m, 1H), 6.22
(s, 1H), 7.32–7.48 (m, 3H), 7.68–
7.74 ppm
(m,
2H);
13C NMR
(75 MHz, CDCl3): d=37.82 (t), 77.98
(t), 88.03 (d), 126.89 (d, 2 C), 128.60 (d, 2 C), 131.52 (d), 134.49 (s),
167.29 (s), 208.00 ppm (s); IR (film): n˜ =3324, 3058, 1957, 1641, 1603,
1578, 1538, 1490, 1428, 1358, 1291, 1267, 1076, 1062, 1030, 852, 802, 738,
Chem. Eur. J. 2011, 17, 5661 – 5667
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5665

A. S. K. Hashmi et al.
713, 696 cmÀ1
calcd for C11H11ON: 173.0841; found:
; HRMS (EI+): m/z
Acknowledgements
173.0842.
This work was supported by Umicore AG & Co. KG and by the Deut-
sche Forschungsgemeinschaft (SFB 623).
Compound 3a: 1H NMR (300 MHz,
CDCl3): d=5.36 (d, 3J=11.3 Hz, 1H),
5.84 (d, 3J=17.6 Hz, 1H), 6.59 (dd,
3J=17.6 Hz, 3J=11.3 Hz, 1H), 7.10 (s,
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1H), 7.41–7.56 (m, 3H), 8.04–8.14 ppm (m, 2H); 13C NMR (75 MHz,
CDCl3): d=114.85 (t), 121.94 (d), 126.04 (d), 126.38 (d, 2 C), 127.36 (s),
128.78 (d, 2 C), 130.42 (d), 150.12 (s), 161.10 ppm (s); IR (film): n˜ =3564,
3536, 3514, 3500, 3491, 3476, 3465, 3451, 3421, 3413, 3394, 3385, 1485,
1449, 1128, 979, 777, 726, 707, 690 cmÀ1; HRMS (EI+): m/z calcd for
C11H9ON: 171.0684; found: 171.0707.
6-Methylidene-2-phenyl-5,6-dihydro-4H-1,3-oxazine (4a) and 2,5-dihydro-
1H-pyrrol-1-ylACHTUNGTRENNUNG(phenyl)methanone (6a): N-(Buta-2,3-dien-1-yl)benzamide
(2a, 80.0 mg, 462 mmol), Ph3PAuCl (11.4 mg, 23 mmol), AgOTs (6.44 mg,
23.0 mmol) and TsOH·H2O (4.39 mg, 23 mmol) were used as described in
GP2. After 2 d reaction time, column chromatography (PE/EA 4:1)
yielded 4a (53 mg,66%, Rf =0.47) as a yellow oil and 6a (10 mg, 13%,
Rf =0.09) as a yellow oil.
Compound 4a: 1H NMR (300 MHz,
CDCl3): d=2.53 (t, 3J=6.2 Hz, 2H),
3.70 (t, 3J=6.2 Hz, 2H), 4.27 (s, 1H),
4.76 (s, 1H), 7.37–7.51 (m, 3H), 7.96–
8.02 ppm
(m,
2H);
13C NMR
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(75 MHz, CDCl3): d=25.42 (t), 43.31
(t), 90.90 (t), 127.15 (d, 2 C), 128.16
(d, 2 C), 130.75 (d), 132.56 (s), 153.53
(s), 153.57 ppm (s); IR (film): n˜ =3062,
2945, 2863, 1658, 1493, 1450, 1429,
1384, 1346, 1316, 1287, 1250, 1213,
1170, 1111, 1069, 1046, 1022, 840, 774,
694, 671, 504 cmÀ1; HRMS (EI+): m/z
calcd for C11H11ON: 173.0841; found:
173.0835.
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2H), 5.68 (m, 1H), 5.85 (m, 1H),
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7.31–7.38 (m, 3H), 7.42–7.48 ppm (m,
2H); 13C NMR (75 MHz, CDCl3): d=53.41 (t), 55.80 (t), 125.20 (d),
126.02 (d), 126.81 (d, 2 C), 128.41 (d, 2 C), 129.88 (d), 136.88 (s),
169.94 ppm (s); IR (film): n˜ =3062, 2922, 2860, 1636, 1616, 1575, 1497,
1447, 1419, 1355, 1333, 1272, 1198, 1028, 1001, 960, 805, 784, 723, 700,
666 cmÀ1; HRMS (EI+): m/z calcd for C11H11ON: 173.0841; found:
173.0847.
6-Methyl-2-phenyl-4H-1,3-oxazine (5a): N-(Buta-2,3-dien-1-yl)benzamide
(2a, 100 mg, 577 mmol), Ph3PAuCl (14.4 mg, 28.8 mmol), AgOTs (8.05 mg,
28.8 mmol) and TsOH·H2O (5.49 mg, 28.8 mmol) were treated as de-
scribed in GP2. After 1 d reaction
time, column chromatography (PE/EA
2:1) yielded 4a (53 mg, 53%, Rf =
0.55) as a yellow oil and 5a (5 mg,
5%, Rf =0.67) as a yellow oil.
Compound 5a: 1H NMR (300 MHz,
CDCl3): d=1.81 (m, 3H), 4.06 (m,
2H), 4.64 (m, 1H), 7.28–7.40 (m, 3H),
7.84–7.89 ppm (m, 2H); 13C NMR
(75 MHz, CDCl3): d=18.55 (q), 43.18
(t), 96.55 (d), 127.14 (d, 2 C), 128.13
(d, 2 C), 130.83 (d), 132.38 (s), 147.01 (s), 153.64 ppm; IR (film): n˜ =
1723, 1683, 1658, 1599, 1522, 1486, 1450, 1389, 1362, 1254, 1197, 1069,
708, 611, 590, 572, 557, 542, 527, 511 cmÀ1 (s); HRMS (EI+): m/z calcd
for C11H11ON: 173.0841; found: 173.0852.
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[19] CCDC-807791 (6 f) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via www.ccdc.cam.
ac.uk/data_request/cif.
5666
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Chem. Eur. J. 2011, 17, 5661 – 5667

Gold Catalysis: 1,3-Oxazines by Cyclisation of Allene Amides
FULL PAPER
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nary frequency.
Received: January 13, 2011
Published online: April 12, 2011
Chem. Eur. J. 2011, 17, 5661 – 5667
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www.chemeurj.org
5667