The first example of rhodium(I)-catalyzed regioand stereoselective chloroesterification of alkynes with chloroformate esters [8]

Full text of DOI:10.1021/ja9822299

J. Am. Chem. Soc. 1998, 120, 12365-12366
12365
and NOE experiments (e.g., 12 and 6% enhancement between
the allylic and the olefinic hydrogens in 3a and 4a, respectively)
confirm that cis-addition has taken place.
The First Example of Rhodium(I)-Catalyzed Regio-
and Stereoselective Chloroesterification of Alkynes
with Chloroformate Esters
Screening of various catalysts (GC yield and 3a/4a ratio are
shown for each case) in the reaction of 1 with 2a under the same
conditions revealed that RhCl(CO)(PPh3)2 (87%, 97/3), RhCl-
(cod)(PPh3) (cod ) 1,5-cyclooctadiene; 91%, 97/3), and RhBr-
(cod)(PPh3) (91%, 98/2) are the catalysts of choice. The use of
Vaska-type rhodium complexes having diphosphine ligands, such
as dppf (1,1′-bis(diphenylphosphino)ferrocene; 55%, 94/6), dppe
(1,2-bis(diphenylphosphino)ethane; 31%, 94/6), and dppb (1,4-
bis(diphenylphosphino)butane; 26%, 91/9) gave high regioselec-
tivities, but the yields were modest. Other rhodium complexes
ligated by more basic phosphines such as RhCl(CO)(PPh2Me)2
(67%, 84/16), RhCl(CO)(PPhMe2)2 (6%, 85/15), RhCl(CO)-
(PMe3)2 (3%, 58/42), RhCl(cod)(PPhMe2) (19%, 64/36), and
RhCl(cod)(PMe3) (5%, 65/35) resulted in lower yields and/or
lower regioselectivities than RhCl(CO)(PPh3)2 and RhCl(cod)-
(PPh3). The activity of IrCl(CO)(PPh3)2 was very low, resulting
in less than 1% yield. Rhodium complexes, either phosphine-
free or having three phosphine ligands, such as [RhCl(cod)]2,
RhCl(PPh3)3, and RhH(CO)(PPh3)3, did not form the product at
all.6
Ruimao Hua, Shigeru Shimada, and Masato Tanaka*
National Institute of Materials and Chemical Research
Tsukuba, Ibaraki 305-8565, Japan
ReceiVed June 26, 1998
Hydroesterification of alkynes with carbon monoxide and
alcohols1 or with formate esters2 is a process of great practical
importance. However, the corresponding chloroesterification reac-
tion, which provides a one-step synthesis of â-chloro-R,â-
unsaturated esters with much synthetic potential,3 has never been
reported. In recent years we have been interested in transition
metal complex-catalyzed addition reactions of E-E′ bonds (E,
E′ ) heteroatom or functional group) to alkynes in order to
synthesize doubly functionalized alkenes in a single step.4
Research in this area has led to the discovery of the efficient
chloroesterification of alkynes with chloroformates (E ) Cl, E′
) COOR).
In a representative experiment, a mixture of 1-hexyne 1 (0.2
mmol), methyl chloroformate 2a (0.6 mmol), and a catalytic
amount of RhCl(CO)(PPh3)2 (0.002 mmol) dissolved in toluene
(0.5 mL) was heated at 110 °C for 10 h. GC and GC-MS
analyses suggested the formation of methyl (Z)-3-chloro-2-
heptenoate 3a and its regioisomer 4a in a ratio of 97:3 (eq 1; R
Ethyl 2b and benzyl 2c chloroformates also reacted with high
regio- and stereoselectivities to afford (Z)-adducts in 95 and 87%
isolated yields with ratios (in the isolated product) of 3b/4b )
100/0 and 3c/4c > 99/1, respectively. Phenyl chloroformate 2d
reacted fairly slowly and with less regioselectivity to afford a
60% total yield with 3d/4d ) 72/18.
The procedure can be readily scaled up and applied to other
alkynes (Table 1).7 The RhCl(CO)(PPh3)2-catalyzed addition of
2a to 1-octyne gave an 86% yield of a 3e and 4e mixture in a
regioisomeric ratio of 96:4. Other aliphatic alkynes substituted
by a phenyl group, a bulky tert-butyl group, and functional groups
such as chloro, cyano, and siloxy also reacted giving high
regioselectivities. However, the reaction of methyl propargyl ether
was rather complicated and gave the (Z)-adduct in only 25% yield.
On the other hand, the reactions of aromatic alkynes were very
clean. Thus, the reaction of phenylacetylene or 1-chloro-4-
ethynylbenzene with 2a gave methyl (Z)-â-chlorocinnamate 3l
or methyl (Z)-â-chloro-p-chlorocinnamate 3m as essentially the
sole product.8 Similarly, the reaction of 4-ethynyltoluene with
2a afforded methyl (Z)-â-chloro-p-methylcinnamate 3n, the
configuration of which was confirmed by X-ray crystrallography.9
Two ester groups could be readily introduced to 1,4-diethynyl-
benzene under the same reaction conditions to give 3p as the
sole product. However, all attempts to chloroesterify internal
alkynes and alkenes under similar conditions have been unsuc-
cessful to date, and the starting materials were recovered.
As far as RhCl(CO)(PR3)2 complex catalysts are concerned,
the reaction can be rationalized by the mechanism illustrated in
Scheme 1, which is partially substantiated by the following
observations. Thus treatment of RhCl(CO)(PR3)2 complexes with
) n-C4H9, R′ ) Me). Evaporation followed by column chroma-
tography (silica gel, 2:1 hexanes-ether) afforded a mixture of
these in 79% isolated yield (3a/4a ) 99/1). Spectroscopic data
for these products are consistent with the proposed structures,5
(1) Review: (a) Pino, P.; Braca, G. In Organic Syntheses Via Metal
Carbonyls; Pino, P., Wender, I. Eds.; John Wiley and Sons: New York, 1977;
Vol. 2, pp 419-516. Recent publications: (b) Hiyama, T.; Wakasa, N.; Ueda,
T.; Kusumoto, T. Bull. Chem. Soc. Jpn. 1990, 63, 640. (c) Scrivanti, A.;
Chinellato, R.; Matteoli, U. J. Mol. Catal. 1993, 84, L141. (d) Kushino, Y.;
Itoh, K.; Miura, M.; Nomura, M. J. Mol. Catal. 1994, 89, 151. (e) Gabriele,
B.; Salerno, G.; Costa, M.; Chiusoli, G. P. J. Organomet. Chem. 1995, 503,
21. (f) Xu, W.; Alper, H. Macromolecues 1996, 29, 6695-6699. (g) Piotti,
M. E.; Alper, H. J. Org. Chem. 1997, 62, 8484-8489. (h) Scrivanti, A.;
Beghetto, V.; Campagna, E.; Zanato, M.; Matteoli, U. Organometallics 1998,
17, 630.
(2) (a) Alper, H.; Saldana-Maldonado, M.; Lin, I. J. B. J. Mol. Catal. 1988,
49, L27. (b) El Ali, B.; Alper, H. J. Mol. Catal. 1991, 67, 29. (c) Zargarian,
D.; Alper, H. Organometallics 1993, 12, 712. (d) El Ali, B.; Alper, H. J.
Mol. Catal. 1995, 96, 197.
(3) For examples, see: (a) Youssef, A.-H. A.; Abdel-Maksond, H. M. J.
Org. Chem. 1975, 40, 3227. (b) Youssef, A.-H. A.; Sharaf, S. M.; El-Sadany,
S. K.; Hamed, E. A. J. Org. Chem. 1981, 46, 38136. (c) Seitz, D. E.; Lee,
S.-H. Tetrahedron lett. 1981, 22, 4909. (d) Chalchat, J.-C.; Garry, R.-P.,
Lacroix; B., Michet, A.; Vessiree, R. C. R. Hebd. Seances Acad. Sci., Ser. 2
1983, 296, 253. (e) Jalander, L.; Broms, M. Acta Chem. Scand. 1983, 37,
173. (f) Barluenga, J.; Fernandez, J. R.; Yus, M. J. Chem. Res., Synop. 1986,
273. (g) Grandjean, D.; Pale, P.; Chuche, J. Tetrahedron 1993, 49, 5225. (h)
Mori, Y.; Asai, M.; Kawade, J.; Furukawa, H. Tetrahedron 1995, 51, 5315.
(4) (a) Han, L.-B.; Tanaka, M. J. Am. Chem. Soc. 1996, 118, 1571. (b)
Han, L.-B.; Choi, N.; Tanaka, M. J. Am. Chem. Soc. 1996, 118, 7000. (c)
Han, L.-B.; Choi, N.; Tanaka, M. Organometallics 1996, 15, 3259. (d)
Onozawa, S.-Y.; Hatanaka, Y.; Sakakura, T.; Shimada, S.; Tanaka, M.
Organometalics 1996, 15, 5450. (e) Onozawa, S.-Y.; Hatanaka, Y.; Tanaka,
M. Chem. Commun. 1997, 1229. (f) Han, L.-B.; Hua, R.; Tanaka, M. Angew.
Chem., Int. Ed. Engl. 1998, 37, 94.
(6) In the reaction using [RhCl(cod)]2, both ClCOOMe and 1-hexyne
remained unreacted; however, the use of RhCl(PPh3)3 or RhH(CO)(PPh3)3
completely decomposed ClCOOMe, but 1-hexyne remained essentially intact.
In the latter case, a large quantity of chloromethane was observed by 1H and
13C NMR spectroscopy.
(7) A typical procedure: A mixture of 1 (410.0 mg, 5.0 mmol), 2a (1410.0
mg, 15.0 mmol), and RhCl(cod)(PPh3) (25.4 mg, 0.05 mmol) in toluene (3.0
mL) was heated under nitrogen in a 25-mL autoclave at 110 °C for 10 h.
After cooling, the solution was concentrated under reduced pressure. The
residue was chromatographed on a silica gel column (hexane:ether ) 2:1) to
give the colorless oil adducts in 80% yield (705.0 mg, 4.0 mmol).
(8) Although the structures were not elucidated, traces of a dimer and a
trimer were found by GC and GC-MS to be formed in the reaction of
phenylacetylene. However, the 1-chloro-4-ethynylbenzene reaction did not
form the corresponding byproducts at all.
(5) Reduction of 3a to (Z)-3-chloro-2-hepten-1-ol 5 further confirmed the
structure.
(9) See Supporting Information for details of the crystal data.
10.1021/ja9822299 CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/13/1998

12366 J. Am. Chem. Soc., Vol. 120, No. 47, 1998
Table 1. Chloroesterification of Terminal Alkynesa
Communications to the Editor
Scheme 1
analysis.11 The 31P{H} NMR spectra of 6a-d showed only one
1
doublet (12.9 to -2.83 ppm; JRh-P ) 88.2-82.4 Hz).12 The H
NMR spectroscopy of 6c displayed phosphine methyl signals as
two apparent 1/2/1 triplets due to the virtual coupling. Likewise,
6b and 6d displayed one apparent 1/2/1 triplet. These 31P and 1H
NMR spectroscopic data, in conjunction with previous observa-
tions,13 suggest that complex 6 has the configuration shown in
Scheme 1. Complex 6b, when heated with 1-hexyne (3 equiv) at
110 °C for 3 h, gave a 93:7 mixture of 3a and 4a in 28% total
yield. Regarding the alkyne insertion process, chlororhodation
(insertion into Rh-Cl) may be more likely in view of the
regioselectivity of the catalysis than alkoxycarbonylrhodation
(insertion into Rh-COOR), which must proceed through con-
gested internal attachment of rhodium.14,15
Further investigations to clarify the mechanism and synthetic
application of the products are in progress.
Acknowledgment. We thank the Japan Science and Technology
Corporation (JST) for financial support through the CREST (Core
Research for Evolutional Science and Technology) program and for a
postdoctoral fellowship to R.H.
Supporting Information Available: Text describing experimental
details, spectroscopic and analytical details of adducts 3a-p and rhodium
complexes 6a-d, tables of positional parameters and Beq values,
anisotropic thermal parameters, and bond lengths and angles for 3n (two
molecules) (18 pages, print/PDF). See any current masthead page for
ordering information and Web access instructions.
JA9822299
(10) Oxidative addition of chloroformate with (η5-C5H5)Rh(PMe3)2 is known
to afford [(η5-C5H5)Rh(COOMe)(PMe3)2]Cl. See: Keim, W.; Becker, J. J.
Organomet. Chem. 1989, 372, 447.
(11) Complexes 6a-d are unstable in solution; there exists an equibrilium
between 6 and the starting materials (RhCl(CO)(PR3)2 and ClCOOMe). See
Supporting Information for spectroscopic data.
a The reactions were carried out at 110 °C for 10 h by using 5.0
mmol alkynes, 15.0 mmol methyl chloroformate 2a and 0.05 mmol
RhCl(cod)(PPh3) in 3 mL of toluene. b Isolated yield based on the
alkynes used, and the ratio of 3/4 was determined by GC. c RhCl(CO)(P-
Ph3)2 (0.05 mmol) was used as catalyst. d TBDMS stands for a tert-
butyldimethylsilyl group. e 0.5 mmol alkyne, 3.0 mmol 2a, and 0.01
mmol catalyst were used.
(12) 31P{H} NMR (C6D6): 6a, 12.9 ppm (d, JRh-P ) 88.2 Hz); 6b, 9.77
ppm (d, JRh-P ) 85.4 Hz); 6c, 2.47 ppm (d, JRh-P ) 82.7 Hz); 6d, -2.83
ppm (d, JRh-P ) 82.4 Hz).
(13) Deeming, A.; Shaw, B. L. J. Chem. Soc. A 1969, 597.
(14) Rhodium-catalyzed chloroarylation of alkynes is reported to proceed
via chlororhodation. See: Kokubo, K.; Matsumasa, K.; Miura, M.; Nomura,
M. J. Org. Chem. 1996, 61, 6941.
(15) Incremental additions of PPh3 to the RhCl(cod)(PPh3)-catalyzed
reaction system depressed the catalytic activity, suggesting that generation of
monophosphine rhodium species would be involved, presumably prior to the
alkyne coordination and insertion.
2a at 80 °C afforded RhCl2(CO)(COOMe)(PR3)2 6 (PR3 ) PPh3
(6a), PPh2Me (6b), PPhMe2 (6c), PMe3 (6d)),10 which were
confirmed by their NMR and IR spectra and/or elemental