Highly regio- and stereoselective acylboration, acylsilation, and acylstannation of allenes catalyzed by phosphine-free palladium complexes: An efficient route to a new class of 2-acylallylmetal reagents

Article abstract of DOI:10.1021/ja036021l

A new method for the synthesis of substituted 2-acylallylmetal reagents in a highly regio- and stereoselective fashion involving a three-component assembly of allenes, acyl chlorides, and bimetallic reagents (B-B, Si-Si, and Sn-Sn) catalyzed by phosphine-free palladium complexes is described. Treatment of various allenes (CR²R³=C=CH₂) with acyl chlorides (R¹COCl) and bispinacolatodiboron in the presence of PdCl₂(CH₃CN)₂ in toluene at 80 °C gave 2-acylallylboronates CR²R³=C(COR¹)CH ₂B-(OCMe₂CMe₂O) in moderate to good yields. The acylsilation of allenes with acid chlorides and hexamethyldisilane (5) proceeded successfully in the presence of Pd(dba)₂ in CH ₃CN affording the corresponding allylsilanes (CR²R ³=C(COR¹)CH₂SiMe₃) in good to moderate yields. Several chloroformates (R⁴OCOCl) also react with 1,1-dimethylallene (2a) and 5 to afford allylsilanes (CR²R ³=C(COOR⁴)CH₂-SiMe³) in 66-70% yields. Acylstannation of allenes could also be achieved by slow addition of hexabutylditin (10) to the reaction mixture of acyl chloride (or chloroformate) and allene 2a in CH₃CN in the presence of Pd(dba)2 at 60 °C; the corresponding 2-substituted allylstannanes were isolated in moderate to good yields. The above catalytic reactions are completely regioselective and highly stereoselective. A mechanism is proposed to account for the catalytic reactions and the stereochemistry.

Full text of DOI:10.1021/ja036021l

Published on Web 09/18/2003
Highly Regio- and Stereoselective Acylboration, Acylsilation,
and Acylstannation of Allenes Catalyzed by Phosphine-Free
Palladium Complexes: An Efficient Route to a New Class of
2-Acylallylmetal Reagents
Feng-Yu Yang, Muthian Shanmugasundaram, Shih-Yih Chuang, Po-Jen Ku,
Ming-Yuan Wu, and Chien-Hong Cheng*
Contribution from the Department of Chemistry, Tsing Hua UniVersity,
Hsinchu, Taiwan, 300 ROC
Received May 8, 2003; E-mail: chcheng@mx.nthu.edu.tw
Abstract: A new method for the synthesis of substituted 2-acylallylmetal reagents in a highly regio- and
stereoselective fashion involving a three-component assembly of allenes, acyl chlorides, and bimetallic
reagents (B-B, Si-Si, and Sn-Sn) catalyzed by phosphine-free palladium complexes is described.
Treatment of various allenes (CR2R3dCdCH2) with acyl chlorides (R1COCl) and bispinacolatodiboron in
the presence of PdCl2(CH3CN)2 in toluene at 80 °C gave 2-acylallylboronates CR2R3dC(COR1)CH2B-
(OCMe2CMe2O) in moderate to good yields. The acylsilation of allenes with acid chlorides and
hexamethyldisilane (5) proceeded successfully in the presence of Pd(dba)2 in CH3CN affording the
corresponding allylsilanes (CR2R3dC(COR1)CH2SiMe3) in good to moderate yields. Several chloroformates
(R4OCOCl) also react with 1,1-dimethylallene (2a) and 5 to afford allylsilanes (CR2R3dC(COOR4)CH2-
SiMe3) in 66-70% yields. Acylstannation of allenes could also be achieved by slow addition of hexabutylditin
(10) to the reaction mixture of acyl chloride (or chloroformate) and allene 2a in CH3CN in the presence of
Pd(dba)2 at 60 °C; the corresponding 2-substituted allylstannanes were isolated in moderate to good yields.
The above catalytic reactions are completely regioselective and highly stereoselective. A mechanism is
proposed to account for the catalytic reactions and the stereochemistry.
1. Introduction
palladium-catalyzed coupling reactions of allenes are highly
useful providing the opportunity to generate complex molecular
frameworks in an efficient manner.3 Recent efforts from our
laboratories revealed that allenes are useful substrates for three-
component assembling reactions.4 Phosphine-free palladium
complexes are efficient catalysts for this type of reaction. This
process presumably involves an oxidative addition of organic
electrophile to the Pd(0) catalyst to give an organopalladium-
(II) intermediate. Insertion of allene into the metal-carbon bond
of organopalladium intermediate generates a π-allylpalladium
complexes that is relatively stable to â-hydride elimination.
Attack of the π-allyl species by a nucleophile leads to the three-
component assembling product. Other groups have developed
phosphine palladium-catalyzed three-component assembling
reactions of allenes.5,6 Shimizu and Tsuji reported a phosphine
palladium-catalyzed coupling of allenes with aryl iodides and
The transition metal-catalyzed addition of an electrophile and
a nucleophile to an unsaturated carbon-linkage is a powerful
method in organic synthesis for the construction of two carbon-
carbon bonds from three different components.1 In the design
of these three-component assembling reactions, the control of
both regio- and stereoselectivity is an important consideration.
In addition, it is necessary to suppress competitive reactions
such as direct coupling of the electrophile and nucleophile,
â-hydride elimination, and polymerization of the alkene. It is a
great challenge for synthetic chemists to develop new three-
component assembling reactions in a highly regio- and stereo-
selective fashion.
The metal-mediated allene chemistry has been the subject of
intense interest for the past two decades.2 In particular,
(1) (a) Chatani, N.; Amishiro, N.; Murai, S. J. Am. Chem. Soc. 1991, 113,
7778. (b) Nakamura, H.; Shim, J. G.; Yamamoto, Y. J. Am. Chem. Soc.
1997, 119, 8113. (c) Wang, Z.; Lu, X.; Lei, A.; Zhang, Z. J. Org. Chem.
1998, 63, 3806. (d) Ikeda, S. I.; Cui, D. M.; Sato, Y. J. Am. Chem. Soc.
1999, 121, 4712. (e) Jeganmohan, M.; Shanmugasundaram, M.; Cheng,
C.-H. Org. Lett. 2003, 5, 881.
(2) (a) Tsuji, J. Organic Synthesis with Palladium Compounds; Springer-
Verlag: New York, 1980. (b) Hegedus, L. S. Transition Metals in the
Synthesis of Complex Organic Molecules; University Science Books: Mill
Valley, CA, 1994. (c) Yamamoto, Y.; Radhakrishnanan, U. Chem. Soc.
ReV. 1999, 28, 199. (d) Zimmer, R.; Dinesh, C. U.; Nandanam, E.; Khan,
F. A. Chem. ReV. 2000, 100, 3067. (e) Hashmi, A. S. K. Angew. Chem.,
Int. Ed. 2000, 39, 3590.
(3) (a) Larock, R. C.; Berrios-Pena, N. G.; Fried, C. A. J. Org. Chem. 1991,
56, 2615. (b) Xiao, W. J.; Alper, H. J. Org. Chem. 1999, 64, 9646. (c)
Grigg, R.; Liu, A.; Shaw, D.; Suganthan, S.; Woodall, D. E.; Yoganathan,
G. Tetrahedron Lett. 2000, 41, 7125. (d) Gai, X.; Grigg, R.; Collard, S.;
Muir, J. E. Chem. Commun. 2001, 1712. (e) Grigg, R.; Khamnaen, T.;
Rajviroongit, S.; Sridharan, V. Tetrahedron Lett. 2002, 43, 2601.
(4) (a) Wu, M.-Y.; Yang, F.-Y.; Cheng, C.-H. J. Org. Chem. 1999, 64, 2471.
(b) Wu, M.-Y.; Yang, F.-Y.; Cheng, C.-H. Tetrahedron Lett. 1999, 40,
6055. (c) Huang, T.-H, Chang, H.-M.; Wu, M.-Y.; Cheng, C.-H. J. Org.
Chem. 2002, 67, 99. (d) Jeganmohan, M.; Shanmugasundaram, M.; Cheng,
C.-H. Chem. Commun. 2003, 1746.
(5) Shimizu, I.; Tsuji, J. Chem. Lett. 1984, 233.
9
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J. AM. CHEM. SOC. 2003, 125, 12576-12583
10.1021/ja036021l CCC: $25.00 © 2003 American Chemical Society

Allenes Catalyzed by Phosphine-Free Pd Complexes
A R T I C L E S
amines.5 Cazes and co-workers have demonstrated the reaction
of allenes with malonates and vinyl halides or vinyl triflates
catalyzed by palladium phosphine complexes.6 However, these
phosphine palladium-catalyzed reactions suffer from the draw-
back of low regio- and stereoselectivity.5,6 Although several
types of electrophiles such as aryl iodides, vinyl iodides, and
viny triflates have been used,4-6 acyl halides as electrophiles
have not been explored in the three-component assembling
reactions of allenes.
Scheme 1
Allylboranes form an important class of organometallic
compounds that have been proven to be versatile synthetic
intermediates in organic synthesis. The addition of allylboranes
to aldehydes is an attractive method for the preparation of
homoallylic alcohols;7 the reaction has been extensively used
for the synthesis of natural products.8 In addition, the coupling
of allylboranes with aryl halides in Suzuki coupling reactions
is well-known.9 A common method for preparing allylboranes
involves a palladium-catalyzed coupling of allylic electrophiles
with tetraalkoxydiboron10 and triethylborane.11 But, this method
generally gave very poor regio- and stereoselectivity. Other
methods for the preparation include regio- and stereoselective
platinum-catalyzed coupling of allyl halides with pinacolborane12
and platinum-catalyzed diboration of allenes.13 Recently, we
discovered an efficient regio- and stereoselective route to
2-borylallylboronates via diboration of allenes catalyzed by
palladium complexes and organic iodides.14
synthetic method for a wide range of 2-acylallylmetal reagents
from easily available starting materials that are difficult to
prepare by other methods.
2. Results and Discussion
In view of the great synthetic utility of allylboranes, the
development of a novel and efficient method for the synthesis
of these reagents in a regio- and stereoselective fashion would
be highly valuable. Our continuing interest in the metal-mediated
allene chemistry4,15 prompted us to explore the possibility of
using acyl chlorides as electrophiles in three-component as-
sembling reactions of allenes. In a preliminary communication,
we reported a palladium-catalyzed highly regio- and stereose-
lective three-component assembly of allenes, acyl chlorides, and
diboron leading to 2-acylallylboronates.16 Herein, we wish to
report the full details of this acylboration reaction and the
extension of this methodology to acylsilation and acylstannation
of allenes. These catalytic reactions provide a convenient
2.1. Palladium-Catalyzed Acylboration of Allenes. The
reaction of toluoyl chloride (1a) with 1,1-dimethylallene (2a)
and bis(pinacolato)diboron (3) at 60 °C for 10 h in the presence
of PdCl2(MeCN)2 (5.0 mol %) in toluene gave 2-acylallyl-
boronate 4a in 81% yield (Scheme 1). No other regioisomer
was detected as evidenced by the 1H NMR spectrum of the crude
reaction mixture. This catalytic three-component assembling
reaction is completely regioselective with the toluoyl and the
boryl group adding to the middle and unsubstituted terminal
carbons of the allene moiety. The presence of a carbonyl group
in 4a is revealed by the observation of a resonance at 201.2
ppm in the 13C NMR spectrum and a strong absorption at 1655
cm-1 in the IR spectrum of this product. Control experiments
indicated that, in the absence of palladium catalyst, no three-
component assembling product 4a was observed.
(6) (a) Ahmar, M.; Barieuz, J.-J.; Cazes, B.; Gore´, J. Tetrahedron 1987, 43,
513. (b) Chaptal, N.; Colovray-Gotteland, V.; Grandjean, C.; Cazes, B.;
Gore´, J. Tetrahedron Lett. 1991, 32, 1795.
(7) (a) Hoffmann, R. W. Angew. Chem., Int. Ed. Engl. 1982, 21, 555. (b)
Matteson, Synthesis 1986, 973. (c) Hoffmann, R. W.; Neil, G.; Schlapbach,
A. Pure Appl. Chem. 1990, 62, 1993. (d) Roush, W. R. In ComprehensiVe
Organic Synthesis; Trost, B. M. Heathcock, C. M., Eds.; Pergamon Press:
Oxford, 1991; Vol. 2, p 1. (e) Brown, H. C.; Ramachandran, P. V. Pure
Appl. Chem. 1991, 63, 307. (f) Vaultier, M.; Carboni, B. In ComprehensiVe
Organometallic Chemistry II; Abel, E. W.; Stone, F. G. A., Wilkinson, G.,
Eds.; Pergamon Press: Oxford, 1995; Vol. 11, pp 191-276.
To understand the nature of the catalytic reaction, the catalytic
activities of various palladium complexes for the reaction of
1a with 2a and 3 in toluene were studied. At 60 °C, Pd(dba)2
and Pd(OAc)2 were effective catalysts affording 4a in 79 and
77%, respectively, but PdCl2(PPh3)2 was completely ineffective
for the reaction. The use of PdCl2(MeCN)2 at 80 °C afforded
4a in 82% yield. The addition of 1 equiv of PPh3 relative to
the PdCl2(CH3CN)2 solution strongly retarded the catalytic
reaction. An examination of the effect of solvent on the yield
of 4a using PdCl2(CH3CN)2 as the catalyst reveals that toluene
was the solvent of choice. Other solvents such as THF and CH3-
CN were also effective affording 4a in 75 and 77% yields,
respectively. The absence of phosphine ligand in the palladium
complex is crucial for the three-component assembling reaction
to proceed smoothly. The above optimization studies led us to
employ the following standard procedure for the acylboration
of various allenes: acyl chloride (0.55 mmol), allene (1.0 mmol),
diboron (0.50 mmol), and 5.0 mol % of PdCl2(MeCN)2 in
toluene at 80 °C.
(8) Chemler, S. R.; Roush, W. R. In Modern Carbonyl Chemistry; Otera, J.,
Ed.; Wiley-VCH: Weinheim, 2000; Chapter 11.
(9) (a) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457. (b) Suzuki, A. In
Metal-Catalyzed Cross-Coupling Reactions; Diederich, F., Stang, P. J., Eds.,
Wiley-VCH: Weinheim, Germany, 1988; Chapter 2. (c) Suzuki, A. J.
Organomet. Chem. 1999, 576, 147.
(10) (a) Ishiyama, T.; Ahiko, T.-a.; Miyaura, N. Tetrahedron Lett. 1996, 37,
6889. (b) Ahiko, T.-a.; Ishiyama, T.; Miyaura, N. Chem. Lett. 1997, 811.
(11) Kimura, M.; Kiyama, I.; Tomizawa, T.; Horino, Y.; Tanaka, S.; Tamaru,
Y. Tetrahedron Lett. 1999, 40, 6795.
(12) Murata, M.; Watanabe, S.; Masuda, Y. Tetrahedron Lett. 2000, 41, 5877.
(13) Ishiyama, T.; Kitano, T.; Miyaura, N. Tetrahedron Lett. 1998, 39, 2357.
(14) Yang, F.-Y.; Cheng, C.-H. J. Am. Chem. Soc. 2001, 123, 761.
(15) (a) Chang, H.-M.; Cheng, C.-H. J. Org. Chem. 2000, 65, 1767. (b) Chang,
H.-M.; Cheng, C.-H. Org. Lett. 2000, 2, 3439. (c) Shanmugasundaram,
M.; Wu, M.-S.; Cheng, C.-H. Org. Lett. 2001, 3, 4233. (d) Shanmu-
gasundaram, M.; Wu, M.-S.; Jeganmohan, M.; Huang, C.-W.; Cheng, C.-
H. J. Org. Chem. 2002, 67, 7724. (e) Wu, M.-S.; Shanmugasundaram, M.;
Cheng, C.-H. Chem. Commun. 2003, 718.
(16) For a preliminary communication, see: Yang, F.-Y.; Wu, M.-Y.; Cheng,
C.-H. J. Am. Chem. Soc. 2000, 122, 7122.
9
J. AM. CHEM. SOC. VOL. 125, NO. 41, 2003 12577

A R T I C L E S
Yang et al.
Table 1. Results of Palladium-Catalyzed Three-Component
Assembly of Acid Chlorides 1, Allenes 2, and Diboron 3a
Scheme 2
4-8). The reaction with 1-naphthonyl chloride (1i) proceeded
quantitatively, but the reaction with 2-naphthonyl chloride (1j)
gave only a moderate yield of 57% (entries 9 and 10).
Heteroaromatic acyl chlorides, 2-thiophenecarbonyl chloride
(1k), and isooxazole-5-carbonyl chloride (1l) also participated
in the reaction giving 4j and 4k in 71 and 62% yields,
respectively (entries 11 and 12).
Under similar conditions, alkanoyl chlorides including tert-
butylacetyl chloride (1m), isovaleryl chloride (1n), and phenyl-
acetyl chloride (1o) undergo three-component reaction effec-
tively with 2a and 3 to afford 4l-n in 80, 63, and 57% yields,
respectively (entries 13-15). To our surprise, alkanoyl chlorides
react much faster than aroyl chlorides under the standard reaction
conditions. The reaction time required for alkanoyl chloride is
2 h, while for aroyl chloride it is 10 h. The difference in
reactivity was further demonstrated by the following crossover
experiments (Scheme 2). The reaction of the same amounts of
acid chlorides benzoyl chloride (1b) and tert-butylacetyl chloride
(1m) with 2a and 3 in the presence of PdCl2(CH3CN)2 in toluene
at 60 °C for 10 h afforded the corresponding allylboronates 4b
and 4l in 8 and 76% yields, respectively. Under similar reaction
conditions, benzoyl bromide and tert-butylacetyl chloride
compete with 2a and 3 to furnish the corresponding 4b and 4l
in 15 and 60% yields, respectively. The above results strongly
suggest that tert-butylacetyl chloride is more reactive than
benzoyl chloride and benzoyl bromide in the present acylbora-
tion of allene. Although the exact reason for the reactivity
difference is not clear, it seems that the insertion of allene into
the alkanoyl-Pd bond is faster than into the aroyl-Pd bond.17
The present three-component assembling reaction can be
further extended to monosubstituted allenes. Thus, the reaction
of n-butylallene (2b) with 1m and 3 in the presence of
PdCl2(CH3CN)2 is highly regio- and stereoselective affording
4o in a high yield of 91% (entry 16). The stereochemistry of
a All reactions were carried out using acyl chloride (0.55 mmol),
bis(pinacolato)diboron (0.50 mmol), allene (1.00 mmol), PdCl2(CH3CN)2
(0.025 mmol), and toluene (2.0 mL) at 80 °C. b Isolated yield. c Yields
determined by the 1H NMR integration method using mesitylene as an
internal standard are shown in parentheses.
In addition to 1a, a wide range of acyl chlorides 1b-o also
react readily with allene 2a and diboron 3 in the presence of
PdCl2(MeCN)2. Table 1 summarizes the results of these reac-
tions. Treatment of benzoyl chloride (1b) with 2a and 3 afforded
4b in 68% yield (entry 2). The same product was obtained in
67% yield for the reaction of benzoyl bromide (1c) with 2a
and 3 (entry 3). Aroyl chlorides 1d-f bearing an electron-
donating methoxy group at the ortho, meta, and para position
react smoothly with 2a and 3 to give 4c-e in 57, 75, and 61%
yields, respectively (entries 4-6). Aroyl chlorides 1g-h with
electron-withdrawing groups -CO2Me and -NO2 group also
undergo three-component reaction efficiently to give 4f and 4g
in 67 and 77% yields, respectively (entries 7 and 8). The
presence of ortho substituent in the aroyl chloride does not
significantly affect the product yield (entry 4). As expected,
aroyl chlorides with electron-withdrawing groups give higher
yield than those with the electron-donating substituents (entries
1
(E)-allylboronate 4o was established by the typical H NMR
NOE experiments. The acylboration of n-butylallene also
proceeded smoothly with acyl chlorides 1f and 1i to give
products 4p and 4q, respectively, with complete regio- and
extremely high stereoselectivity (entries 17 and 18). Similarly,
the reactions of phenylallene (2c) and cyclohexylallene (2d) with
1m and 3 and also tert-butylallene (2e) with 1a and 3 provided
the corresponding allylboronates 4r, 4s, and 4t in 77, 88, and
(17) (a) Obora, Y.; Tsuji, Y.; Kawamura, T. J. Am. Chem. Soc. 1993, 115, 10414.
(b) Obara, Y.; Tsuji, Y.; Kawamura, T. J. Am. Chem. Soc. 1995, 117, 9814.
9
12578 J. AM. CHEM. SOC. VOL. 125, NO. 41, 2003

Allenes Catalyzed by Phosphine-Free Pd Complexes
A R T I C L E S
Scheme 3
50% yields with high E stereoselectivity (entries 19-21). In
all cases, a single or predominately E isomer was obtained with
an E/Z ratio falling in the narrow range 93/7 to 99/1. The
stereoselectivity of products appears little affected by the
substituent on allenes. However, under similar conditions, the
reaction of 1 and 3 with 1,3-substituted allenes PhCHCCHMe
or Me2CCCMe2 is extremely slow, and no desired product was
observed.
There are several interesting features of the present catalytic
reaction. First, all of the phosphine-free palladium-catalyzed
acylboration of allenes are completely regioselective and highly
stereoselective affording the corresponding 2-acylallylboronates
in good to moderate yields. Second, unlike most transition metal-
mediated addition reactions of acid chlorides, acyl group
regioselectively adds to the allene moiety without decarbonyla-
tion.18 Finally, the catalytic acylboration proceeds smoothly in
the absence of base, in contrast to most transmetalation processes
of diboron that required the assistance of base.19
Scheme 4
2.2. Palladium-Catalyzed Acylsilation of Allenes. Transi-
tion-metal-catalyzed reactions involving organosilanes are useful
for the construction of carbon-carbon bonds in organic
synthesis.20 In particular, allylsilane compounds are extensively
used in carbonyl addition reactions21 and coupling reactions.22
Recently, allylsilanes were employed as key intermediates for
the total syntheses of peduncularine,23a citreoviral,23b allomus-
carine,23c epimuscarine,23c and serotonin antagonist LY426965.23d
The synthetic utility of allylsilanes was further demonstrated
in the metal-catalyzed reaction with dienes24 and alkynes.25
Several methods for the synthesis of allylsilanes catalyzed by
transition metal complexes are known. A palladium-catalyzed
synthesis of allylsilanes via the coupling of allylic acetates with
hexamethyldisilane was reported by Tsuji and co-workers.26
However, the reaction requires a higher temperature and longer
reaction period. The same group also described a palladium-
catalyzed decarbonylative coupling of acid chlorides, allenes,
and disilanes to give the corresponding allylsilanes.17 We have
recently developed a highly regio- and stereoselective synthesis
of allylsilanes by the palladium-catalyzed three-component
assembly of allenes, aryl iodides, and silylstannanes.4a The
observed acylboration of allenes prompted us to examine the
feasibility of acylsilation of allenes. The investigation led
successfully to the synthesis of a new class of 2-acylallylsilanes.
The results are shown below.
Treatment of 1b with 2a and hexamethyldisilane (5) in the
presence of Pd(dba)2 (5.0 mol %) in toluene at 80 °C for 5 h
gave a mixture of products 6a and 7a in 25 and 41% yields,
respectively (Scheme 3). The spectral data of these products
reveal that 6a is a three-component assembling product of allene,
acyl chloride, and disilane, while 7a is a double-allene insertion
product consisting of two molecules of allene, an acyl, and a
silyl group. Similarly, reactions with acyl chlorides 1f and 1p
afforded the corresponding double-allene insertion products 7b
and 7c, respectively, in addition to the normal three-component
assembling products 6b and 6c. These results are greatly
different from the foregoing acylboration of allenes in which
no double-allene insertion occurred.
To improve the selectivity of acylsilation reaction, the effect
of solvent and ligand on the reaction of 1b with 2a and 5 using
Pd(dba)2 as the catalyst was investigated. To our delight, the
reaction in CH3CN gave only acylsilation product 6a in 80%
yield with no double-allene insertion product 7a detected. THF
is also a suitable solvent for the acylsilation of allenes, affording
6a exclusively in 76% yield. However, no catalytic reaction
occurred in DMF. At 60 °C, the yield of 6a is lower (63%)
than that obtained at 80 °C. Similar to acylboration of allenes,
the presence of phosphine ligands such as 4 equiv of PPh3, 1
equiv of dppe, or 1 equiv of dppf relative to the catalyst strongly
retarded the catalytic acylsilation of allenes. On the basis of
the above results, it appears that CH3CN and palladium
complexes without any phosphine ligand are the solvent and
the catalyst of choice, respectively, for three-component as-
sembling of 1b with 2a and 5. Thus, the following reaction
conditions, allene (1.00 mmol), acyl chloride (1.00 mmol),
disilane (1.20 mmol), Pd(dba)2 (5.0 mol %), CH3CN (2.0 mL),
reaction temperature 80 °C, and reaction time 5 h (Scheme 4),
were chosen as the general reaction conditions for the acyl-
silation of allenes.
(18) (a) Ohno, K.; Tsuji, J. J. Am. Chem. Soc. 1968, 90, 99. (b) Lau, K. S. Y.;
Becker, Y.; Huang, F.; Baenziger, N.; Stille, J. K. J. Am. Chem. Soc. 1977,
99, 5664. (c) Krafft, T. E.; Rich, J. D.; McDermott, P. J. J. Org. Chem.
1990, 55, 5430.
(19) (a) Ishiyama, T.; Murata, M.; Miyaura, N. J. Org. Chem. 1995, 60, 7508.
(b) Ishiyama, T.; Itoh, Y.; Kitano, T.; Miyaura, N. Tetrahedron Lett. 1997,
38, 3447.
(20) (a) Colvin, E. W. Silicon in Organic Synthesis; Butterworth: London, 1981;
pp 97-124. (b) Weber, W. P. Silicon Reagents for Organic Synthesis;
Springer: Berlin, 1983; pp 173-205. (c) Colvin, E. W. Silicon Reagents
in Organic Synthesis; Academic: London, 1988; pp 25-37. (d) Patai, S.;
Rappoport, Z., Eds. The chemistry of Organic Silicon Compounds; Wiley:
Chichester, U.K., 1988; Part 2. (e) Fleming, I.; Barbero, A.; Walter, D.
Chem. ReV. 1997, 97, 2063.
(21) For a recent review on allylmetal addition, see: (a) Denmark, S. E.;
Almstead, N. G. In Modern Carbonyl Chemistry; Otera, J., Ed.; Wiley-
VCH: Weinheim, 2000; Chapter 10. (b) StereoselectiVe Synthesis, Methods
of Organic Chemistry (Houben-Weyl), Edition E21; Helmchen, G.,
Hoffmann, R., Mulzer, J., Schaumann, E., Eds.; Thieme: Stuttgart, 1996;
Vol. 3, p 1357.
(22) Hiyama, T. In Metal-Catalyzed Cross-Coupling Reactions; Diederich, F.;
Stang, P. J.; Eds.; Wiley-VCH: Weinheim, 1998; Chapter 10.
(23) (a) Roberson, C. W.; Woerpel, K. A. J. Am. Chem. Soc. 2002, 124, 11246.
(b) Peng, Z. H.; Woerpel, K. A. Org. Lett. 2002, 4, 2945. (c) Angle, S. R.;
El-Said, N. A. J. Am. Chem. Soc. 2002, 124, 3608. (d) Denmark, S. E.;
Fu, J. Org. Lett. 2002, 4, 1951.
(24) Castan˜o, A. M.; Ba¨ckvall, J.-E.; J. Am. Chem. Soc. 1995, 117, 560. (b)
Castan˜o, A. M.; Persson, B. A.; Ba¨ckvall, J.-E. Chem.sEur. J. 1997, 3,
482.
(25) Ferna´ndez-Rivas, C.; Me´ndez, M.; Nieto-Oberhuber, C.; Echavarren, A.
M. J. Org. Chem. 2002, 67, 5197.
(26) Tsuji, Y.; Kajita, S.; Isobe, S.; Fuanato, M. J. Org. Chem. 1993, 58, 3607.
In addition to 1b, a series of aroyl chlorides 1 (1a, 1h, 1j,
1k, and 1q) including electron-donating, electron-withdrawing,
9
J. AM. CHEM. SOC. VOL. 125, NO. 41, 2003 12579

A R T I C L E S
Yang et al.
Table 2. Results of Palladium-Catalyzed Three-Component
Assembly of Acid Chlorides 1, Allenes 2, and Disilane 5 in
CH3CNa
Scheme 5
Similar to acyl chlorides, chloroformates can also be used as
the electrophiles in the catalytic three-component assembling
of allenes (Scheme 5). Various chloroformates including phenyl
chloroformate (8a), benzyl chloroformate (8b), n-butyl chloro-
formate (8c), and isobutyl chloroformate (8d) reacted with 2a
and 5 in the presence of Pd(dba)2 in CH3CN to furnish the
corresponding allylsilanes 9a-d in 68, 70, 68, and 66% yields,
respectively. In all cases, the R4OCO- and silyl groups are
added to the middle and to the terminal carbons, respectively,
of allene 2a, indicating that the catalytic reaction is completely
regioselective. It is noteworthy that this is the first time
chloroformates are employed as electrophiles in the three-
component assembling reaction of allenes.
In addition to the observed high regio- and stereoselectivity,
two intriguing features merit comment for the present acyl-
silation of allenes. First, there is no decarbonylation product
observed in all reactions. For comparison, in the previous
palladium-catalyzed three-component reaction of acyl chlorides,
disilanes, and 1,3-dienes reported by Tsuji et al., decarbonylative
coupling products were formed.17 Second, no direct coupling
product between disilane and acid chloride was found under
the reaction conditions. It is to be noted that direct coupling of
disilanes with acid chlorides catalyzed by palladium complexes
occurs readily as reported in the literature.27
2.3. Palladium-Catalyzed Acylstannation of Allenes. Al-
lylstannanes are versatile synthetic reagents28 that have been
used as key intermediates in the total syntheses of pseudop-
terolide29a,b and epothilones B and D.29b In addition, allylstan-
nanes are extensively employed in coupling reactions30 and
allylation reactions with aldehydes.21,31 A traditional route to
allylstannanes involves palladium-catalyzed couplings of allylic
acetates with Et2AlSnBu3,32 ditin,33 and Bu3SnCl.34 However,
the utility of these reactions is limited by the poor regio- and
stereoselectivity. Another palladium-catalyzed synthesis of
allylstannanes is the coupling of allylic phosphates with
a All reactions were carried out using acyl chloride (1.00 mmol), allene
(1.00 mmol), disilane (1.20 mmol), Pd(dba)2 (0.05 mmol), and CH3CN (2.0
mL) at 80 °C. b Isolated yield. c Yields determined by the 1H NMR
integration method using mesitylene as an internal standard are shown in
parentheses.
and heteroaromatic chlorides all undergo three-component
assembling reactions with 2a and 5 in the presence of Pd(dba)2
in CH3CN affording the corresponding 2-acylallylsilanes 6d-h
in good to moderate yields (Table 2, entries 2-6). The catalytic
acylsilation reaction is highly chemoselective as evidenced by
the results in entries 7 and 8. Under similar reaction conditions,
4-chlorobenzoyl chloride (1r) as well as 4-bromobenzoyl
chloride (1s) react chemoselectively with 2a and 5 to afford
the corresponding 2-acylallylsilanes 6i and 6j in 88 and 87%
yields, respectively. These observations clearly suggest that the
oxidative addition of the ArCO-Cl bond is faster than that of
the Ar-Cl or Ar-Br bond to Pd(0). In addition to aroyl
chlorides, alkanoyl chlorides including tert-butylacetyl chloride
(1m), tert-butylcarbonyl chloride (1t), and n-butylcarbonyl
chloride (1u) undergo three-component assembling with 2a and
5 to afford the corresponding allylsilane products 6k-m, albeit
in lower yields than those from aroyl chlorides (entries 9-11).
The catalytic reaction is also successfully applied to mono-
substituted allenes. Thus, n-butylallene (2b) reacted with 1a and
disilane 5 to furnish the three-component assembly product 6n
in 88% yield (Table 2, entry 12). The catalytic reaction is highly
regio- and stereoselective; no other isomer was detected in the
1H NMR spectrum of the crude reaction mixture. The Z
(27) (a) Yamamoto, Y.; Suzuki, S.; Tsuji, J. Tetrahedron Lett. 1980, 1653. (b)
Eaborn, C.; Griffifths, R.; Pidcock, A. J. Organomet. Chem. 1982, 225,
331. (c) Rich, J. D. J. Am. Chem. Soc. 1989, 111, 5886.
(28) (a) Yamamoto, Y.; Asao, N. Chem. ReV. 1993, 93, 2207. (b) Marshall, J.
A. Chem. ReV. 1996, 96, 31. (c) Davies, A. G. Organotin Chemistry;
VCH: Weinheim, Germany, 1997.
(29) (a) Paquette, L. A.; Rayner, C. M.; Doherty, A. M. J. Am. Chem. Soc.
1990, 112, 4078. (b) Marshall, J. A.; Liao, J. L. J. Org. Chem. 1998, 63,
5962. (c) Martin, N.; Thomas, E. J. Tetrahedron Lett. 2001, 42, 8373.
(30) (a) Pereyre, M.; Quintard, J.-P.; Rahm, A. Tin in Organic Synthesis;
Butterworth: London, 1987. (b) Mitchell, T. N. In Metal-Catalyzed Cross-
Coupling Reactions; Diederich, F., Stang, P. J., Eds.; Wiley-VCH:
Weinheim, Germany, 1998; Chapter 4. (c) Marshall, J. A. Chem. ReV. 2000,
100, 3163.
1
stereochemistry of allylsilane 6n was established by H NMR
(31) (a) Hanawa, H.; Hashimoto, T.; Maruoka, K. J. Am. Chem. Soc. 2003,
125, 1708. (b) Nishigaichi, Y.; Takuwa, A. Tetrahedron Lett. 2003, 44,
1405.
NOE techniques. The reaction with cyclohexylallene (entry 13)
is also highly stereoselective giving (Z)-6o as the sole product,
but the reaction with phenylallene is less stereoselective
affording 6p with an E/Z ratio of 30:37 (entry 14).
(32) Trost, B. M.; Herndon, J. W. J. Am. Chem. Soc. 1984, 106, 6835.
(33) Bumagin, N. A.; Kasatakin, A. N.; Beletkaya, I. P. IzV. Akad. Nauk. SSSR.
Ser. Khim. 1984, 636.
(34) Tabuchi, T.; Inanaga, J.; Yamaguchi, M. Tetrahedron Lett. 1987, 28, 215.
9
12580 J. AM. CHEM. SOC. VOL. 125, NO. 41, 2003

Allenes Catalyzed by Phosphine-Free Pd Complexes
A R T I C L E S
Table 3. Results of Palladium-Catalyzed Three-Component
Assembly of Acid Chlorides 1, Dimethylallene (2a), and Ditin 10a
Scheme 6
Scheme 7
a All reactions were carried out using acyl chloride (1.00 mmol), allene
(1.50 mmol), Pd(dba)2 (0.05 mmol), CH3CN (1.0 mL), and ditin (1.00 mmol)
in CH3CN (1.0 mL), which was added slowly by syringe pump over a period
of 4 h at 60 °C. b Isolated yield.
Scheme 8
Et2AlSnBu3 reported by Oshima and co-workers.35 Recently,
we developed a highly regio- and stereoselective method for
the synthesis of allylic stannanes by the palladium-catalyzed
addition of silylstannanes to allenes.36
The acylstannation of allenes catalyzed by nickel complexes
is known in the literature.37 The catalytic reaction involves
addition of acylstannes to allenes to furnish R-(acylmethyl)-
vinylstannanes. To the best of our knowledge, no example using
palladium-catalyzed acylstannation of allenes has been reported.
The present three-component reaction can be successfully
extended to the synthesis of 2-acylallylstannanes. The results
of this study are summarized in Table 3.
Under conditions similar to the acylboration and acylsilation
of allenes, treating 1a with 2a and hexabutylditin (10) in the
presence of Pd(dba)2 in CH3CN at 60 °C afforded only a trace
amount of three-component assembling product, 2-acylallyl-
stannane 11a. Instead, the major product is tributyl(4-methyl-
benzoyl)stannane formed by a direct coupling of acyl chloride
1a with ditin 10. The observation is surprising in view of the
previously successful results of acylboration and acylsilation
of allenes. The formation of direct coupling product (4-meth-
ylbenzoyl)stannane suggests that the allene insertion step is
relatively slow compared to the reaction of acyl group with ditin
(vide infra). The competing direct coupling reaction was
effectively suppressed by a slow addition of ditin 10 over a
period of 4 h to the reaction mixture of 1a and 2a affording
three-component acylstannation product 11a in 70% yield
(Scheme 6, Table 3, entry 1).
2-7). Like acylsilation of allenes, the present acylstannation
reaction is highly chemoselective (entries 6 and 7). Alkanoyl
chlorides, 1m and 1t also react effectively with 2a and 10 to
give acylstannation products 11i and 11j in 55 and 40% yields,
respectively (entries 9 and 10). In addition to 2-acylallylstan-
nanes, the direct coupling product from acyl chloride and ditin
was formed, but in less than 5% yield in all cases. There is no
desired three-component product observed with monosubstituted
allenes such as phenylallene and cyclohexylallene. The reaction
was messy giving unidentified products as seen in the 1H NMR
spectrum of the crude reaction mixture.
In addition to acyl chlorides, chloroformates also have been
successfully employed in the three-component stannation of
allenes (Scheme 7). The reaction of 8a, 8b, and 8d with 2a and
10 in the presence of the Pd(dba)2/CH3CN system furnished
the corresponding allylstannanes 12a-c in 68, 70, and 66%
yields, respectively.
3. Mechanistic Consideration
Several aroyl chlorides 1 (1g, 1h, 1j, 1k, and 1q-s) also
react smoothly with 2a and 10 to give the corresponding
2-acylallylstannanes 11b-h in good to moderate yields (Table
3, entries 2-8). The catalytic acylstannation reaction tolerates
a variety of functional groups such as ester, nitro, sulfur, chloro,
and bromo on the aromatic ring of the aroyl chlorides (entries
On the basis of the known palladium chemistry and the
foregoing results, a plausible mechanism is proposed in Scheme
8 to account for the present three-component assembling
reactions. The catalytic reaction is likely initiated by the
oxidative addition of acyl chloride to Pd(0) to give acyl Pd(II)
intermediate 13. Coordination followed by insertion of allene
to the Pd-carbon bond produces π-allylpalladium(II) species 14.
Transmetalation of 14 with bimetallic reagents (B-B, Si-Si,
and Sn-Sn) and subsequent reductive elimination of 15 yield
the final product and regenerate the Pd(0) catalyst.
(35) Matsubara, S.; Wakamastu, K.; Morizawa, Y.; Tsuboniwa, N.; Oshima,
K.; Noyaki, H. Bull. Chem. Soc. Jpn. 1985, 58, 1196.
(36) Jeganmohan, M.; Shanmugasundaram, M.; Chang, K.-J.; Cheng, C.-H.
Chem. Commun. 2002, 2552.
(37) Shirakawa, E.; Nakao, Y.; Hiyama, T. Chem. Commun. 2001, 263.
9
J. AM. CHEM. SOC. VOL. 125, NO. 41, 2003 12581

A R T I C L E S
Yang et al.
Scheme 9
with high stereoselectivity. It is necessary that the latter step is
faster than the syn-anti rearrangement of the π-allylpalladium
species to obtain high stereoselectivity. The anti form of 14a is
responsible for the high stereoselectivity of the present catalytic
reaction. In the reported phosphine-palladium-mediated three-
component reaction of allenes,5,6 the observed low stereoselec-
tivity is probably due to the rapid syn-anti rearrangement of
the π-allylpalladium species through a σ-allylpalladium inter-
mediate assisted by the phosphine ligands.39
The same proposed mechanism in Scheme 8 satisfactorily
accounts for the acylboration, acylsilation, and acylstannation
of allenes, but the relative rate of each step in the catalytic cycle
may be different for each of these three-component assembling
reactions. For the acylboration, acylsilation, and acylstannation
of allenes, the rates of oxidative addition of acyl chloride to
Pd(0) to give 13 and the insertion of allene into the acyl-
palladium(II) bond in 13 are expected to be the same for all
these reactions, if the same catalyst and solvent were used for
the catalytic reactions. On the other hand, the transmetalation
step is different for different acylmetalation reactions of allene.
Based on the foregoing observations that (i) only three-
component acylboration of allene took place in toluene; (ii)
double insertion of allene occurred for acylsilation of allene in
toluene; and (iii) slow addition of ditin 10 is necessary to achieve
successful acylstannation of allene, we can conclude that the
relative rate of transmetalation is ditin 10 > diboron 3 > disilane
5.
Scheme 10
Although the reason for the exclusive formation of acylsilation
product in CH3CN or THF is not entirely clear, it is likely that
these molecules are coordinated to the palladium center, for
instance, to intermediate 14 in Scheme 8. The coordinating
ability and the high concentration of these solvent molecules
prevent further bonding of a second allene molecule to the
palladium complex and completely inhibit the double-allene
insertion process.
The facile formation of 2-acylallylic metal reagents without
decarbonylation is an important characteristic feature of the
present acylmetallation reactions. The results indicate that, in
the present three-component assembling reactions, the addition
of the acyl-palladium bond to allene is faster than decarbonyla-
tion of the acyl-palladium intermediate. However, in the
palladium-catalyzed decarbonylative reaction of acid chlorides,
disilanes, and 1,3-dienes reported by Tsuji, the acyl-palladium
intermediate readily undergoes decarbonylation prior to addition
to 1,3-dienes.17 The facile insertion of allenes into an acyl-
palladium(II) bond can be attributed to the highly energetic
carbon-carbon double bonds of allenes (1,2-dienes) relative to
those of 1,3-dienes.
A modification of the mechanism shown in Scheme 8 can
account for the formation of double-allene insertion product 7.
Intermediate 16 instead of undergoing transmetalation may
further react with another allene molecule via coordination and
then insertion to give a new π-allylpalladium complex 17 as
depicted in Scheme 9. Transmetalation of 17 with disilane
affords intermediate 18. Subsequent reductive elimination of
18 gives double-insertion product 7 and regenerates the Pd(0)
catalyst.
The highly stereoselective formation of either E or Z isomers
from monosubstituted allenes is an attractive feature of the
present methodology. It is to be noted that most carbopalladation
reactions of monosubstituted allenes gave a mixture of E and Z
isomeric products with a low degree of selectivity.38 To account
for the high stereoselectivity, a mechanism involving face-
selective coordination of allenes to the palladium center is
proposed (Scheme 10). The terminal double bond of allene is
bonded to the palladium moiety at the face opposite to the
substituents R2 favorably to avoid steric congestion. On the other
hand, coordination of the terminal double bond of allene to the
palladium center at the other face with R2 syn to the palladium
center or coordination of the internal double bond of allene to
the palladium center will lead to an increase of steric repulsion
and is less likely. As shown in Scheme 10, the face-selective
coordination results in a π-allylpalladium species 14a with the
R2 group anti to the acyl moiety. Further reaction with bimetallic
reagents (B-B, Si-Si, Sn-Sn) affords 2-acylallylmetal reagents
4. Conclusions
We have successfully developed a new phosphine-free
palladium-catalyzed three-component assembly of allenes, acyl
chlorides, and bimetallic reagents (B-B, Si-Si, and Sn-Sn).
This method leads to a new class of 2-acylallylmetal reagents
in good to moderate yields. This is the first time that acyl
chlorides are used as electrophiles in the three-component
coupling reactions of allenes. In addition, chloroformtes are also
used for the first time in these reactions. It is noteworthy that
(38) (a) Yamamoto, Y.; Al-Masum, M.; Asao, N. J. Am. Chem. Soc. 1994, 116,
6019. (b) Besson, L.; Gore´, J.; Cazes, B. Tetrahedron Lett. 1995, 36, 3853.
(c) Vicrat, N.; Cazes, B.; Gore´, J. Tetrahedron 1996, 52, 9101. (d) Larock,
R. C.; Tu, C.; Pace, P. J. Org. Chem. 1998, 63, 6859. (e) Larock, R. C.;
He, Y.; Leong, W. W.; Han, X.; Refvik, M. D.; Zenner, J. M. J. Org.
Chem. 1988, 53, 2154.
(39) (a) Powell, J.; Shaw, B. L. J. Chem. Soc. A 1967, 1839. (b) Tibbtets, D.
L.; Brown, T. L. J. Am. Chem. Soc. 1970, 92, 3031.
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12582 J. AM. CHEM. SOC. VOL. 125, NO. 41, 2003

Allenes Catalyzed by Phosphine-Free Pd Complexes
A R T I C L E S
was stirred at 60 °C for 10 h. The crude reaction mixture was diluted
with toluene (50 mL), and the mixture was washed with brine (25 mL)
3 times. The organic layer was dried over anhydrous magnesium sulfate
and concentrated in vacuo. The yields of 4b and 4l were determined
by the H NMR integration method using mesitylene as an internal
standard.
no decarbonylative coupling product was observed in all of these
reactions. The acylboration of allenes proceeds smoothly in the
absence of base. For acylsilation of allenes, CH3CN appears to
be the best solvent to achieve exclusive three-component
acylsilation product, while, in toluene, acylsilation of allenes
afforded a mixture of three-component acylsilation and double-
allene insertion products. The successful acylstannation reaction
was realized by the slow addition of ditin reagent to the reaction
mixture of allene and acyl chloride. The presence of phosphine
ligands strongly retarded the present 2-acylallylmetalation
reaction. The methodology is compatible with a wide variety
of functional groups tested. The catalytic reaction is completely
regioselective in which the acyl group and metal add to the
middle and unsubstituted terminal carbon of the allene moiety,
respectively. In addition, the reaction is highly stereoselective
in the case of monosubstituted allenes. The mechanism involving
a face-selective coordination of allenes is proposed to account
for the high stereoselectivity.
1
General Procedure for the Reaction of Acyl Chloride 1 with
Allene 2a, and Disilane 5 in Toluene. To a 25-mL sidearm flask was
added Pd(dba)2 (0.050 mmol). The system was evacuated and purged
with nitrogen several times. Acyl chloride (1.00 mmol), dimethylallene
(1.00 mmol), hexamethyldisilane (1.20 mmol), and toluene (2.0 mL)
were added to the system, and the reaction mixture was stirred at
80 °C for 5 h. The crude reaction mixture was diluted with CH2Cl2
(50 mL), filtered through Celite and silica gel, and concentrated in
vacuo. The residue was chromatographed on a silica gel column
(hexane/EtOAc ) 9/1) to give products 6 and 7. Compounds 6a-c
and 7a-c were prepared according to this method. The product yield
of each reaction is listed in Scheme 3.
General Procedure for the Three-Component Assembly of Acyl
Chloride 1 or Chloroformate 8, Allene 2, and Disilane 5 in CH3CN.
To a 25-mL sidearm flask was added Pd(dba)2 (0.050 mmol). The
system was evacuated and purged with nitrogen several times. Acyl
chloride (1.00 mmol) or chloroformate (1.00 mmol), allene (1.00 mmol),
hexamethyldisilane (1.20 mmol), and CH3CN (2.0 mL) were added to
the system, and the reaction mixture was stirred at 80 °C for 5 h. The
crude reaction mixture was diluted with CH2Cl2 (50 mL), filtered
through Celite and silica gel, and concentrated in vacuo. The residue
was chromatographed on a silica gel column (hexane/EtOAc ) 9/1) to
give the desired product. Compounds 6a, 6d-p, and 9a-d were
prepared according to this method. The product yield of each reaction
is listed in Table 2 and Scheme 5.
5. Experimental Section
General Considerations. All reactions were run under a nitrogen
atmosphere on a dual-manifold Schlenk line, unless otherwise men-
tioned, and in oven-dried glassware. All solvents were dried according
to known methods and distilled prior to use.40 PdCl2(CH3CN)2,41 Pd-
(dba)2,42 and allenes43 were prepared by procedures previously reported.
Reagents and chemicals were used as purchased without further
purification. The purity of each product was checked by NMR analysis.
General Procedure for the Three-Component Assembly of Acyl
Halide 1, Allene 2, and Diboron 3. To a 25-mL sidearm flask were
added acyl chloride (0.55 mmol), PdCl2(CH3CN)2 (0.025 mmol, 5.0
mol %), and bis(pinacolato)diboron (3) (0.50 mmol). The system was
evacuated and purged with nitrogen 3 times. Allene (1.00 mmol) in
toluene (2.0 mL) was added to the system, and the reaction mixture
was stirred at 80 °C. After completion of the reaction (the time required
for aroyl chloride is ∼10 h, and for alkanoyl chloride, it is ∼2 h),
toluene (50 mL) was added to the reaction solution and the mixture
was washed with brine (25 mL) 3 times. The organic layer was dried
over anhydrous magnesium sulfate and concentrated in vacuo. The
residue was distilled over Kugelrohr oven to give the desired product.
Compounds 4a-t were prepared according to this method. The product
yield of each reaction is listed in Table 1.
General Procedure for the Three-Component Assembly of Acyl
Chloride 1 or Chloroformate 8, Allene 2a, and Ditin 10. To a 25-
mL sidearm flask was added Pd(dba)2 (0.050 mmol). The system was
evacuated and purged with nitrogen several times. Acyl chloride (1.00
mmol) or chloroformate (1.00 mmol), allene (1.50 mmol), and CH3-
CN (1.0 mL) were added to the system, and the reaction mixture was
stirred at 60 °C. Hexabutylditin (1.00 mmol) in CH3CN (1.0 mL) was
added slowly by syringe pump over a period of 4 h. After the injection
was completed, the reaction was stirred for another 0.5 h. The crude
reaction mixture was diluted with CH2Cl2 (50 mL), filtered through
Celite and silica gel and concentrated in vacuo. The residue was
chromatographed on a silica gel column (hexane/EtOAc ) 9/1) to give
the desired three-component assembly product. Compounds 11a-j and
12a-c were prepared according to this method. The product yield of
each reaction is listed in Table 3 and Scheme 7. The spectral data of
these allylmetal reagents are given in the Supporting Information.
Competitive Reaction of tert-Butylacetyl Chloride (1m) and
Benzoyl Chloride (1b) or Benzoyl Bromide (1c) with Allene 2a and
Diboron 3. To a 25-mL sidearm flask were added PdCl2(CH3CN)2
(0.025 mmol, 5 mol %) and bis(pinacolato)diboron (3) (0.50 mmol).
The system was evacuated and purged with nitrogen 3 times. tert-
Butylacetyl chloride (0.25 mmol), benzoyl chloride (0.25 mmol) or
benzoyl bromide (0.25 mmol), and 1,1-dimethylallene (1.00 mmol) in
toluene (2.0 mL) were added to the system, and the reaction mixture
Acknowledgment. We thank the National Science Council
of the Republic of China (NSC 91-2113-M-007-053) for the
support of this research.
(40) Perin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals,
3rd ed.; Pergamon Press: New York, 1988.
(41) Colquhoun, H. M.; Halton, J.; Thompson, D. J.; Twigg, T. V. New Pathway
for Organic Synthesis-Practical Applications of Transition Metals; Plenum
Press: New York, 1988; p 383.
(42) Takahashi, Y.; Ito, T.; Sakai, S.; Ishii, Y. J. Chem. Soc., Chem. Commun.
1970, 1065.
(43) Brandsma, L.; Verkruijisse, H. D. Synthesis of Acetylene, Allenes and
Cumulenes; Elsevier: New York, 1981.
Supporting Information Available: Spectral data for com-
pounds 4a-t, 6a-p, 7a-c, 9a-d, 11a-j, and 12a-c. This
material is available free of charge via the Internet at
http://pubs.acs.org.
JA036021L
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