Steric hindrance-controlled Pd(O)-catalyzed coupling-cyclization of 2,3-allenamides and organic iodides. An efficient synthesis of iminolactones and γ-hydroxy-γ-lactams

Article abstract of DOI:10.1021/jo025967v

Under the catalysis of 1 mol % Pd(PPh₃)₄, the reaction of 4,4-disubstituted 2,3-allenamides and organic iodides in toluene afforded iminolactones stereospecifically in >90% yields using K₂CO₃ (2 equiv)-5 mol %TBAB as the base. A similar reaction with 4-monosubstituted 2,3-allenamides afforded γ-hydroxy-γ-lactams in relatively lower yields. The N/O-attack selectivity may be determined by the steric effect at the 4-position of 2,3-allenamides.

Full text of DOI:10.1021/jo025967v

SCHEME 1
Ster ic Hin d r a n ce-Con tr olled
P d (0)-Ca ta lyzed Cou p lin g-Cycliza tion of
2,3-Allen a m id es a n d Or ga n ic Iod id es. An
Efficien t Syn th esis of Im in ola cton es a n d
γ-Hyd r oxy-γ-la cta m s
Shengming Ma* and Hexin Xie
State Key Laboratory of Organometallic Chemistry,
Shanghai Institute of Organic Chemistry, Chinese Academy
of Sciences, 354 Fenglin Lu, Shanghai 200032, P. R. China
SCHEME 2
masm@pub.sioc.ac.cn
Received May 24, 2002
Abstr a ct: Under the catalysis of 1 mol % Pd(PPh3)4, the
reaction of 4,4-disubstituted 2,3-allenamides and organic
iodides in toluene afforded iminolactones stereospecifically
in >90% yields using K2CO3 (2 equiv)-5 mol % TBAB as
the base. A similar reaction with 4-monosubstituted 2,3-
allenamides afforded γ-hydroxy-γ-lactams in relatively lower
yields. The N/O-attack selectivity may be determined by the
steric effect at the 4-position of 2,3-allenamides.
SCHEME 3
Recently, much of the attention of our research group
has been paid to the chemistry of allenes.1 The coupling-
cyclization reaction of functionalized allenes provides new
methodologies for the synthesis of carbocycles2 and
heterocycles such as furans,3 2,5-dihydrofurans,4 ox-
iranes,5 and butenolides.6 With the chemistry of 2,3-
allenoic acids6 and esters,7 we envisioned that Pd(0)-
catalyzed coupling-cyclization reaction of 2,3-allenamides
with organic iodides would provide a new synthetic
pathway to pyrrol-2(5H)-ones and 5-hydroxypyrrol-2(5H)-
ones, a class of compounds of biological interest.
In 2000, we developed an efficient methodology for the
synthesis of 4-halo-5-hydroxypyrrol-2(5H)-ones via the
cyclization reaction of 2,3-allenamides with CuX2.8 In this
paper, we report our recent results on the Pd(0)-catalyzed
coupling-cyclization of 2,3-allenamides and organic io-
dides.
SCHEME 4
2,3-Allenamide 1b was prepared by the aminolysis of
the corresponding of 2,3-allenoyl chloride (Scheme 2).10
2,3-Allenamides 1c,d ,h were prepared by the DMAP-
catalyzed amidation of the corresponding 2,3-allenoic
acids with amines (Scheme 3).
P d (0)-Ca ta lyzed Cou p lin g-Cycliza tion of 2,3-Al-
len a m id es a n d Or ga n ic Ha lid es. We initiated this
study with 4-monosubstituted 2,3-allenamides 1a and 1b.
The coupling-lactamization reaction with PhI in DMF
or toluene under the catalysis of Pd(PPh3)4 was followed
by γ-hydroxylation8 to afford 5-hydroxypyrolin-2(5H)-ones
3a and 3b in 45 and 48% yields, respectively (Scheme
4). The structures of these two products were determined
by the X-ray diffraction study of 3b.11
Syn th esis of Sta r tin g Ma ter ia l. 2,3-Allenamides
1a ,e-g were prepared by the palladium-catalyzed car-
bonylation of 1,2-allenic bromide in the presence of
amines (Scheme 1).9
(1) (a) Schuster, H. F.; Coppola, G. M. Allenes in Organic Synthesis;
Wiley & Sons: New York, 1984. (b) Patai, S., Ed.; The Chemistry of
Ketenes, Allenes, and Related Compounds: Wiley & Sons: New York,
1980; Part 1.
(2) Ma, S.; Zhao, S. Org. Lett. 2000, 2, 2495.
(3) Ma, S.; Zhang, J . Chem. Commun. 2000, 117. Ma, S.; Li, L. Org.
Lett. 2000, 2, 941.
(4) Ma, S.; Gao, W. Tetrahedron Lett. 2000, 41, 8933.
(5) Ma, S.; Zhao, S. J . Am. Chem. Soc. 1999, 121, 7943.
(6) Ma, S.; Shi, Z. J . Org. Chem. 1998, 63, 6387. Ma, S.; Duan, D.;
Shi, Z. Org. Lett. 2000, 2, 1419. Ma, S.; Shi, Z.; Yu, Z. Tetrahedron
Lett. 1999, 40, 2393. Ma, S.; Shi, Z.; Yu, Z. Tetrahedron 1999, 55, 12137.
Ma, S.; Wu, S. J . Org. Chem. 1999, 64, 9314.
However, it is surprising to observe that both 2.5 mol
% Pd2(dba)3‚CHCl3-10 mol % PPh3 and 5 mol % Pd-
(7) Ma, S.; Wu, S. Tetrahedron Lett. 2001, 42, 4075.
(8) Ma, S.; Xie, H. Org. Lett. 2000, 2, 3801.
(9) Trieu, N. D.; Elsevier, C. J .; Vrieze, K. J . Organomet. Chem.
1987, 325, C23.
(10) (a) Himbert, G.; Schlindwein, H.-J . Z. Naturforsch 1992, 47b,
1785. (b) Himbert, G.; Schlindwein, H.-J . Liebigs Ann. Chem. 1997,
435.
10.1021/jo025967v CCC: $22.00 © 2002 American Chemical Society
Published on Web 08/14/2002
J . Org. Chem. 2002, 67, 6575-6578
6575

TABLE 1. P d (0)-Ca ta lyzed Cou p lin g-Cycliza tion Rea ction of 1a w ith P h I u n d er Differ en t Con d ition s
catalyst
(mol %)a
Ag2CO3
(mol %)
TBAB
(mol %)
K2CO3
(equiv)
PhI
(equiv)
time
(h)
yield of 4a
entry
solvent
(%)
1
2
3
4
5
6
7
A
5
10
10
none
none
none
5
4
4
4
4
4
2
2
1.3
1.3
1.3
1.3
1.3
1.1
1.1
toluene
toluene
CH3CN
THFb
DMF
toluene
toluene
18.5
18
17
17
17
99
99
92
88
92
67
95
B (5)
B (5)
B (5)
B (5)
C (1)c
B (1)
none
none
none
none
none
none
4 days
47
5
a
b
A ) 2.5 mol % Pd2(dba)3‚CHCl3, 10 mol % PPh3; B ) Pd(PPh3)4. Reflux.
TABLE 2. P d (0)-Ca ta lyzed Syn th esis of Im in ola cton esa
1
2
R5
time
(h)
yield of 4
entry
R1
R2
R3
R4
(%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16b
17b
18b
(CH2)5
(CH2)5
(CH2)5
(CH2)5
(CH2)5
n-Pr
n-Pr
n-Pr
n-Pr
n-Pr
Bn
Bn
Bn
Bn
Bn
H
H
H
H
H
Me
Me
Me
Bn (1c)
Bn (1c)
Bn (1c)
Bn (1c)
Bn (1c)
Bn (1d )
Bn (1d )
Bn (1d )
Bn (1d )
Bn (1d )
Bn (1e)
Bu (1f)
H (1g)
Ph (2a )
p-MeC6H4 (2b)
47
47
65
72
44
65
48
65
72
72
22
24
22
22
22
17
20
20
95 (4a )
95 (4b)
95 (4c)
94 (4d )
100 (4e)
96 (4f)
92 (4g)
93 (4h )
94 (4i)
96 (4j)
90 (4k )
91 (4l)
94 (4m )
93 (4n )
90 (4o)
75 (4p )
99 (4q)
99 (4r )
p-MeOC6H4 (2c)
p-NO2C6H4 (2d )
p-MeO2CC6H4 (2d )
Ph (2a )
p-MeC6H4 (2b)
p-MeOC6H4 (2c)
p-NO2C6H4 (2d )
p-MeO2CC6H4 (2d )
Ph (2a )
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Ph (2a )
p-MeC6H4 (2b)
p-MeOC6H4 (2c)
p-MeO2CC6H4 (2d )
(E)-1-hexenyl
(Z)-2-MeO2CCHdCH
(E)-2-MeO2CCHdCH
H (1g)
H (1g)
Bn (1h )
Bn (1h )
Bn (1h )
a
b
Reaction was carried out using 0.25 mmol of 1 and 2 (1.1 equiv) in 2 mL of toluene. 5% Pd(PPh3)4 and 1.5 equiv of R5I were used.
(PPh3)4 can catalyze the reaction of 2,3-allenamides 1c
with PhI to afford the unexpected iminolactone 4a in
99% yield (entries 1 and 2, Table 1). The correspond-
ing reactions in MeCN, THF, and DMF in the presence
of K2CO3 gave 4a in slightly lower yields (entries 3-5,
Table 1). Finally, it was observed that the reaction
with 1 mol % Pd(PPh3)4 in toluene using K2CO3 (2
equiv)-5 mol % TBAB (tetra(n-butyl) amonium bromide)
as the base (defined as conditions A) afforded the product
4a in 95% yield after 47 h (entry 7, Table 1). With 1 mol
% catalyst, the reaction with TBAB worked somewhat
more cleanly. With cyclic palladium complex 5 as the
catalyst, the yield of 4a dropped to 67% (entry 6, Table
1).
With conditions A as the standard conditions, the
reaction went smoothly to give products 4 in excellent
yields. Some of the typical results are summarized in
Table 2. From the results shown in Table 2, the following
points are noteworthy. (1) The structures of the imino-
lactones were unambiguously determined by the X-ray
diffraction studies of products 4f and 4o.12 Only the
stereoisomer with R4 orientated toward the cyclic oxygen
was formed, which may be attributed to the steric
hindrance between R3 and R4. (2) In most cases, 1 mol %
Pd(PPh3)4 is sufficient to provide the products 4 in
excellent yields. (3) The R4 group can be Bn, n-Bu, or H.
(4) R3 can be an Bn, H, or an alkyl group. (5) Both
electron-deficient and electron-rich aryl halides can be
(11) CCDC 178889. Crystal Data for 3b: C23H25NO2, MW ) 347.44,
monoclinic, space group P2(1)/n, Mo KR, final R indices [I > 2σ(I)], R1
) 0.0374, wR2 ) 0.0675, a ) 11.0641(10) Å, b ) 6.5484(6) Å, c ) 26.977-
(3) Å, R ) 90°, â ) 93.537(2)°, γ ) 90°, T ) 293(2) K, Z ) 4, reflections
collected/unique: 11472/4586 (Rint ) 0.0510), no observation [I > 2σ-
(I)] 2001, parameters 335.
6576 J . Org. Chem., Vol. 67, No. 18, 2002

SCHEME 5
Exp er im en ta l Section
Syn th esis of 1a ,e-g: Gen er a l P r oced u r e. A stainless steel
autoclave (250 mL) fitted with a glass reactor with a stirring
bar inside was charged with THF (50 mL), 1,2-allenyl bromide
(27.8 mmol), Et3N (30.6 mmol), and Pd(PPh3)4 (0.28 mmol)
sequentially. The autoclave was charged with CO with
a
pressure of 25 atm. After the mixture was stirred for 2 h at rt,
CO was released. The reaction was quenched with water
followed by the addition of CH2Cl2. After separation, the organic
phase was washed sequentially with 1 N HCl and brine. After
evaporation, the residue was purified by flash chromatography
on silica gel to afford allenamides 1a ,e-g.
N-Ben zyl Oct a -2,3-d ien a m id e (1a ): white solid, mp 70-
72 °C (petroleum ether); 1H NMR (300 MHz, CDCl3) δ 7.35-
7.24 (m, 5H), 6.18 (bs, 1H), 5.63-5.56 (m, 2H), 4.47 (d, J ) 5.7
Hz, 2H), 2.15-2.07 (m, 2H), 1.45-1.28 (m, 4H), 0.87 (t, J ) 7.2
Hz, 3H); 13C NMR (75.4 MHz, CDCl3) δ 207.48, 165.12, 138.27,
128.58, 127.57, 127.36, 96.90, 91.20, 43.52, 30.77, 27.53, 22.06,
13.69; MS m/z 229 (M+, 1.78), 91 (100); IR (KBr) 3268, 1960,
1628 cm-1; Anal. Calcd for C15H19NO: C, 78.56; H, 8.35; N, 6.11
Found: C, 78.45; H, 8.49; N, 5.92.
Syn th esis of 1b. In a dry flask containing 4-cyclohexylbuta-
2,3-dienoic acid (833 mg, 5 mmol) was added SOCl2 (1 mL, 14
mmol). After stirring for 30 min at rt, the excess SOCl2 was
removed under reduced pressure to afford 4-cyclohexylbuta-2,3-
dienoyl chloride, which was dissolved in dry ether (10 mL) for
conversion in the next step.
applied. (6) The reaction of 4,4-disubstituted 2,3-allena-
mides with 1-alkenyl iodides also afforded the corre-
sponding iminolactams in good to excellent yields. The
configurations of the CdC bond in 1-alkenyl iodides
remained intact (entries 16-18, Table 2).
To a mixture of benzylamine (0.6 mL, 5.5 mmol) and Et3N
(0.78 mL, 5.5 mmol) in dry ether (20 mL) was added 4-cyclo-
hexylbuta-2, 3-dienoyl chloride in dry ether dropwise at rt. After
the mixture was stirred for 3 h, the precipitate was removed by
filtration and the solvent was evaporated to afford the residue,
which was purified by flash chromatography on silica gel to
afford 732 mg (57%) of N-Ben zyl 4-cycloh exylbu ta -2,3-d i-
en a m id e (1b): white solid, mp 118-120 °C (petroleum ether/
diethyl ether); 1H NMR (300 MHz, CDCl3) δ 7.35-7.23 (m, 5H),
6.20 (bs, 1H), 5.67-5.58 (m, 2H), 4.47 (d, J ) 5.7 Hz, 2H), 2.15-
2.08 (m, 1H), 1.79-1.61 (m, 5H), 1.34-1.06 (m, 5H); 13C NMR
(75.4 MHz, CDCl3) δ 206.68, 165.15, 138.32, 128.55, 127.46,
127.31, 102.66, 92.04, 43.45, 36.79, 32.78, 32.65, 25.77, 25.71,
25.70; MS m/z 255 (M+, 20.67), 91 (100); IR (KBr) 3281, 1958,
1628 cm-1. Anal. Calcd for C17H21NO: C, 79.96; H, 8.29; N, 5.49.
Found: C, 79.95; H, 8.39; N, 5.33.
Syn th esis of 1c,d ,h . To a 50 mL dry flask containing allenoic
acid (5.25 mmol) and dry CH2Cl2 (10 mL) were added sequen-
tially a solution of DCC (5.5 mmol) and DMAP (0.26 mmol) in
dry CH2Cl2 (5 mL) and a solution of benzylamine (5.8 mmol) in
dry CH2Cl2 (5 mL) at -30 °C. After the mixture was stirred at
room temperature for 6 h, the precipitate was removed by
filtration. After evaporation, the residue was purified by flash
chromatography on silica gel to afford allenamides 1c,d ,h .
N-Ben zyl 3-Cycloh exylid en e-2-p r op yla cr yla m id e (1c):
white solid, mp 63-65 °C (petroleum ether); 1H NMR (300 MHz,
CDCl3) δ 7.36-7.24 (m, 5H), 6.21 (bs, 1H), 4.48 (d, J ) 5.7 Hz,
2H), 2.26 (t, J ) 7.5 Hz, 2H), 2.18-2.15 (m, 4H), 1.59-1.41 (m,
8H), 0.93 (t, J ) 7.4 Hz, 3H); 13C NMR (75.4 MHz, CDCl3) δ
198.98, 167.33, 138.83, 128.59, 127.35, 127.22, 108.94, 100.86,
43.54, 31.06, 29.78, 27.56, 25.81, 21.25, 13.64; MS m/z 283 (M+,
38.18), 91 (100); IR (KBr) 3324, 1954, 1637 cm-1. Anal. Calcd
for C19H25NO: C, 80.52; H, 8.89; N, 4.94. Found: C, 80.37; H,
9.16; N, 4.67.
From this study, it is interesting to observe that in the
reaction of 4,4-disubstituted-2,3-allenamides, the nucleo-
philicity of the carbonyl oxygen is much higher than that
of the amido nitrogen atom. The reaction is believed to
proceed via a mechansim consisting of an oxidative
addition reaction, a π-allyl palladium intermediate-
forming carbopalladation reaction, and an exclusive
intramolecular nucleophilic attack of the carbonyl oxygen
followed by the loss of H+; this generates the CdN bond
to afford iminolactones11-13 (for 4,4-disubstituted 2,3-
allenamides) or intramoleculer nucleophilic attack of the
nitrogen atom to form γ-lactams, which can be further
oxidized to γ-hydroxy-γ-lactams (for 4-monosubstituted
2,3-allenamides) (Scheme 2). The N-/O- attack selectiv-
ity may be attributed to the steric hindrance at the
4-positions of 2,3-allenamides. They were synthesized
from the aminolysis of thionophthalides13 and cyclization
of γ-hydroxy-nitriles14 or -oxazolines.15 Due to the gen-
erality, high yield, diversity, and highly setereoselective
nature of this reaction, it will show its potential in
organic synthesis.
(12) CCDC 178890 and 178891. Crystal Data for 4f: C26H25NO, MW
) 367.47, monoclinic, space group P2(1)/c, Mo KR, final R indices [I >
2σ(I)], R1 ) 0.0875, wR2 ) 0.1686, a ) 18.289(6) Å, b ) 11.795(4) Å, c
) 19.888(7) Å, R ) 90°, â ) 101.744(5)°, γ ) 90°, T ) 293(2) K, Z ) 8,
reflections collected/unique: 20293/7365 (Rint ) 0.2424), no observation
[I > 2σ(I)] 849, parameters 509. Crystal Data for 4o: C14H15NO3, MW
) 245.27, orthorhombic, space group Pnma, Mo KR, final R indices [I
> 2σ(I)], R1 ) 0.0386, wR2 ) 0.0772, a ) 13.8655(14) Å, b ) 7.1721(7)
Å, c ) 12.5108(12) Å, R ) 90°, â ) 90°, γ ) 90°, T ) 293(2) K, Z ) 4,
reflections collected/unique: 7316/1606 (Rint ) 0.0508), no observation
[I > 2σ(I)] 861, parameters 144.
(13) Pirkle, W. H.; Sowin, T. J . J . Org. Chem. 1987, 52, 3011.
(14) (a) Parham, W. E.; J ones, L. D. J . Org. Chem. 1976, 41, 1187.
(b) Ducker, J . W.; Gunter, M. J . Aust. J . Chem. 1974, 27, 2229.
(15) (a) Mart´ınez, M. M.; OÄ nega, M. G.; Tellado, M. F.; Seijas, J . A.;
Va´zquez-Tato, M. P. Tetrahedron 1997, 53, 14127. (b) Dordor, I. M.;
Mellor, J . M. J . Chem. Soc., Perkin Trans. 1 1984, 1247.
1-Ben zyl-5-b u t yl-5-h yd r oxy-4-p h en ylp yr r ol-2(5H )-on e
(3a ). To a mixture of potassium carbonate (97 mg, 0.70 mmol)
and Pd(PPh3)4 (20 mg, 0.017 mmol) in DMF (2 mL) were added
allenamide 1a (80 mg, 0.35 mmol) and iodobenzene (60 µL, 0.53
mmol) sequentially under Ar. After the mixture was stirred at
70 °C for 9 h, water was added and the reaction mixture was
extracted with ether. The organic layer was washed with brine
and dried over anhydrous sodium sulfate. After evaporation, the
residue was purified by flash chromatography on silica gel to
afford 50 mg (45%) of 3a : white solid, mp 178-180 °C (n-
hexane-CH2Cl2); 1H NMR (300 MHz, CDCl3) δ 7.71-7.66 (m,
2H), 7.38-7.13 (m, 8H), 6.18 (s, 1H), 4.59 (d, J ) 15.4 Hz, 1H),
J . Org. Chem, Vol. 67, No. 18, 2002 6577

4.38 (d, J ) 15.0 Hz, 1H), 3.62 (bs, 1H), 1.80-1.72 (m, 2H), 0.78-
0.36 (m, 7H); 13C NMR (75.4 MHz, CDCl3) δ 169.89, 158.96,
138.65, 131.22, 130.37, 129.07, 128.86, 128.66, 127.68, 127.58,
121.07, 94.56, 41.95, 34.95, 25.08, 22.13, 13.76; MS m/z 321 (M+,
resulting mixture was heated to 70 °C for 47 h. After evapora-
tion, the residue was purified by flash chromatography on silica
gel to afford 84 mg (95%) of 4a :
N-Ben zyl
(4-P h en yl-3-p r op yl-1-oxa -sp ir o[4,5]d ec-3-
3.42), 91 (100); IR (KBr) 3120, 1675 cm-1. Anal. Calcd for C21H23
-
en ylid en e) Am in e (4a ): light yellow solid, mp 71.5-72 °C (n-
hexane); 1H NMR (300 MHz, CDCl3) δ 7.37-7.03 (m, 10H), 4.61
(s, 2H), 2.06 (t, J ) 7.7 Hz, 2H), 1.64-1.35 (m, 11H), 1.05-090
(m, 1H), 0.72 (t, J ) 7.4 Hz, 3H); 13C NMR (75.4 MHz, CDCl3)
δ 163.69, 158.16, 141.84, 134.07, 131.41, 128.62, 128.57, 128.33,
128.21, 127.94, 126.33, 89.93, 51.20, 34.44, 26.39, 24.86, 22.38,
21.87, 14.20; MS m/z 359 (M+, 93.68), 358 (100); IR (KBr) 1681
cm-1. Anal. Calcd for C25H29NO: C, 83.52; H, 8.13; N, 3.90.
Found: C, 83.81; H, 8.04; N, 3.73.
NO2: C, 78.47; H, 7.21; N, 4.36. Found: C, 78.53; H, 7.34; N,
4.32.
1-Be n zyl-5-c-h e xyl-5-h yd r oxy-4-p h e n ylp yr r ol-2(5H )-
on e (3b ). To a mixture of potassium carbonate (83 mg, 0.60
mmol), TBAB (5 mg, 0.016 mmol), and Pd(PPh3)4 (17 mg, 0.015
mmol) in toluene (2 mL) were added allenamide 1b (77 mg, 0.30
mmol) and iodobenzene (52 µL, 0.45 mmol) sequentially under
Ar. The resulting mixture was heated to 70 °C for 30 h to afford
50 mg (48%) of 3b: white solid, mp 198-200 °C (n-hexane-CH2-
Cl2); 1H NMR (300 MHz, CDCl3) δ 7.61-7.58 (m, 2H), 7.35-
7.12 (m, 8H), 5.96 (s, 1H), 4.57 (d, J ) 15.4 Hz, 1H), 4.37 (d, J
) 15.4 Hz, 1H), 4.06 (bs, 1H), 1.73-1.28 (m, 6H), 0.82-0.42 (m,
5H); 13C NMR (75.4 MHz, CDCl3) δ 170.75, 160.91, 138.57,
133.69, 129.87, 128.77, 128.68, 128.54, 128.14, 127.34, 122.83,
96.71, 44.11, 42.49, 27.16, 26.84, 26.72, 26.12, 26.07; MS m/z
347 (M+, 9.15), 91 (100); IR (KBr) 3270, 1665 cm-1. Anal. Calcd
for C23H25NO2: C, 79.51; H, 7.25; N, 4.03. Found: C, 79.20; H,
7.26; N, 3.67.
Ack n ow led gm en t. We are grateful to the Major
State Basic Research Development Program (Grant
G2000077500) and National Natural Science Founda-
tion of China for financial support. Shengming Ma is
the recipient of the 1999 Qiu Shi Award for Young
Chinese Scientific Workers issued by the Hong Kong
Qiu Shi Foundation of Science and Technology.
P d (0)-Ca ta lyzed Cou p lin g-Cycliza tion of 2,3-Allen a -
m id es a n d Ar yl Iod id es. Typ ica l P r oced u r e for Syn th esis
of 4a . To a mixture of potassium carbonate (68 mg, 0.49 mmol),
TBAB (4 mg, 0.012 mmol), and Pd(PPh3)4 (3 mg, 0.0026 mmol)
in toluene (2 mL) were added allenamide 1c (70 mg, 0.25 mmol)
and iodobenzene (32 µL, 0.28 mmol) sequentially under Ar. The
Su p p or tin g In for m a tion Ava ila ble: Analytical data for
all starting materials and products not listed in the text. This
material is available free of charge via the Internet at
http://pubs.acs.org.
J O025967V
6578 J . Org. Chem., Vol. 67, No. 18, 2002