8600
J. Am. Chem. Soc. 2001, 123, 8600-8601
Cleavage of Carbon-Carbon Triple Bond of Alkyne
via Hydroiminoacylation by Rh(I) Catalyst
Scheme 1
Chul-Ho Jun,* Hyuk Lee, Choong Woon Moon, and
Hye-Sook Hong
Department of Chemistry, Yonsei UniVersity
Seoul 120-749, Korea
ReceiVed April 26, 2001
The cleavage of carbon-carbon bonds has become one of the
1
most challenging subjects in organic chemistry. Despite remark-
able progress in this area, alkyne cleavage has been demonstrated
Table 1. The C-C triple bond cleavage of alkynes
only on a few examples including alkyne-ligand scission on metal
entry
allylamine (1)
alkyne (2)
isolated yield (%)
2
3
complexes and oxidative cleavage in addition to alkyne meta-
1
2
1
2
3
4
5
6
7
8
1a (R ) Ph)
2a (R ) CH
3
)
98 (3a)
84 (3b)
93 (3c)
91 (3d)
4
thesis. Moreover, most of them are not efficient enough to be
1
2
1a (R ) Ph)
3 7
2b (R ) n-C H )
utilized for synthetic purpose. Therefore, we attempted to develop
a catalytic process to cleave C-C triple bonds by utilizing our
chelation-assisted hydroacylation methodology established in
pursuit of C-H and C-C bond activation.5 Described herein is
a novel one-pot protocol for the catalytic cleavage of C-C triple
bonds through hydroiminoacylation of alkyne followed by amine-
assisted C-C double bond cleavage of the resulting R,â-
unsaturated ketimine. As in the schematic representation (Scheme
1
2
1a (R ) Ph)
2 5
2c (R ) n-C H )
1
2
1a (R ) Ph)
2d (R ) n-C H )
5
11
1
2
a
1a (R ) Ph)
2e (R ) Ph)
98 (3e)
,6
1
2
b
1b (R ) CH
3
3
)
)
2b (R ) n-C
3
H
7
)
80 (3f)
1
2
a
1b (R ) CH
2e (R ) Ph)
94 (3g)
1
2
a
1c (R ) H)
2e (R ) Ph)
92 (3h)
a
The reaction was carried out with 6. b GC yield.
1
), the C-C triple bond of alkyne 2 is divided into (i) an aldehyde
crotylamine 1b and allylamine 1c were used in addition to
3-phenylallylamine 1a. All reactions exhibited fairly good yields
(80-98%) of the corresponding alkyne cleavage product 3.
and (ii) the alkylmethylene unit of ketone 3 formed by the
combination of allylamine 1, an acyl equivalent.
When the reaction of allylamine 1a and 2-butyne (2a, 1.2 equiv
of 1a) was carried out at 130 °C for 12 h in the presence of Rh-
3 3
(PPh ) Cl (4, 3 mol %), cyclohexylamine (5, 200 mol %) and
benzoic acid (6, 5 mol %), ketimine 7a was determined in a
quantitative yield by GC analysis along with aldimine 8a (eq 1).
Hydrolysis of imine 7a gave 1-phenyl-pentan-3-one (3a) in a 98%
7
isolated yield. Eventually, both ethylidene moiety of aldimine
8a and ethyl group of ketimine 7a were derived from the C-C
triple bond cleavage of 2-butyne (2a). This C-C bond cleavage
was investigated with a variety of symmetric alkynes 2 including
aliphatic and aromatic alkynes as shown in Table 1.8 And
The mechanism of this transformation is proposed as in Scheme
2
. The first step should be the isomerization of allylamine 1 to
(
1) For reviews, see: (a) Rybtchinski, B.; Milstein, D. Angew. Chem., Int.
Ed. 1999, 38, 870. (b) Jennings, P. W.; Johnson, L. L. Chem. ReV. 1994, 94,
2
241. (c) Crabtree, R. H. Chem. ReV. 1985, 85, 245. (d) Murakami, M.; Ito,
Scheme 2. Plausible Mechanism for Triple Bond Cleavage of
Alkyne
Y. In ActiVation of UnreactiVe Bonds and Organic Synthesis; Murai, S. Ed.;
Springer: Berlin, 1999; pp 97-129.
(
2) (a) Morris, M. J. In Metal Clusters in Chemistry; Braunstein, P., Oro,
L. A., Raithby, P. R., Eds.; Wiley-VCH: Weinheim, 1999; Vol. 1; pp 221-
2
35. (b) Cairns, G. A.; Carr, N.; Green. M.; Mahon, M. F. Chem. Commun.
996, 2431. (c) O’Connor, J. M.; Pu, L. J. Am. Chem. Soc. 1990, 112, 9013.
1
(
d) Degani, Y.; Willner, I. J. Chem. Soc., Chem. Commun. 1985, 648. (e)
Sullivan B. P.; Smythe, R. S.; Kober, E. M.; Meyer, T. J. J. Am. Chem. Soc.
982, 104, 4701. (f) Hayashi, N.; Ho, D. M.; Pascal, R. A., Jr. Tetrahedron
Lett. 2000, 41, 4261.
1
(3) (a) Moriarty, R. M.; Penmasta, R.; Awasthi, A. K.; Prakash, I. J. Org.
Chem. 1988, 53, 6124. (b) Sawaki, Y.; Inoue, H.; Ogata, Y. Bull. Chem. Soc.
Jpn. 1983, 56, 1133.
(4) (a) For a review, see: Bunz, U. H. F.; Kloppenburg, L. Angew. Chem.,
Int. Ed. 1999, 38, 478. (b) F u¨ rstner, A.; Grela. K.; Mathes, C.; Lehmann, C.
W. J. Am. Chem. Soc. 2000, 122, 11799. (c) F u¨ rstner, A.; Mathes, C.;
Lehmann, C. W. J. Am. Chem. Soc. 1999, 121, 9453. (d) F u¨ rstner, A.; Seidel,
G. Angew. Chem., Int. Ed. 1998, 37, 1734. (e) Kloppenburg, L.; Song, D.;
Bunz, U. H. F. J. Am. Chem. Soc. 1998, 120, 7973. (f) McCullough, G. L.;
Schrock, R. R. J. Am. Chem. Soc. 1984, 106, 4067. (g) Montreux, A.;
Blanchard, M. J. Chem. Soc., Chem. Commun. 1974, 786.
(
5) For C-H bond activation, see: (a) Jun, C.-H.; Lee, D.-Y.; Lee, H.;
Hong, J.-B. Angew. Chem., Int. Ed. 2000, 39, 3070. (b) Jun, C.-H.; Lee, H.;
Hong, J.-B. J. Org. Chem. 1997, 62, 1200. (c) Jun, C.-H.; Lee, D.-Y.; Hong,
J.-B. Tetrahedron Lett. 1997, 38, 6673.
(
6) For C-C bond activation, see: (a) Jun, C.-H.; Lee, H.; Lim, S.-G. J.
Am. Chem. Soc. 2001, 123, 751. (b) Jun, C.-H.; Lee, H. J. Am. Chem. Soc.
999, 121, 880.
7) Acetaldehyde generated from hydrolysis of aldimine 8a was evaporated
during isolation.
8) With a terminal alkyne, no desired product was observed, due to its
extremely poor reactivity to hydroiminoacylation with allylamine 1.
1
aldimine, followed by a C-H bond cleavage of aldimine by Rh-
(
9
(I) to yield iminoacylrhodium(III) hydride 9. The hydrometalation
(
(9) Jun, C.-H.; Lee, H.; Park. J.-B.; Lee, D.-Y. Org. Lett. 1999, 1, 2161.
1
0.1021/ja011053z CCC: $20.00 © 2001 American Chemical Society
Published on Web 08/08/2001