C O M M U N I C A T I O N S
RhCl(dppb)(PPh3) catalyzes the isomerization of alkylacetylene-
derived propargyl alcohols to the corresponding indanones in
relatively high yields (66-67% yield; eq 8).
In summary, we have developed a rhodium-catalyzed isomer-
ization of R-arylpropargyl alcohols to indanones under mild
conditions. Considering the ease of preparation of these substrates
(terminal alkynes + aromatic aldehydes), this method provides a
new way of constructing indanones with high efficiency. In addition,
by the mechanistic investigations using deuterium-labeled substrates,
we have disclosed that the reaction goes through an unexpected
cascade, with a 1,4-hydrogen shift being the turnover-limiting step
of the catalytic cycle.
Acknowledgment. Support has been provided in part by a
Grant-in-Aid for Scientific Research, the Ministry of Education,
Culture, Sports, Science and Technology, Japan (21 COE on Kyoto
University Alliance for Chemistry).
Supporting Information Available: Experimental procedures and
compound characterization data (PDF). This material is available free
References
(1) For reviews, see: (a) Trost, B. M.; Krische, M. J. Synlett 1998, 1. (b)
Fairlamb, I. J. S. Angew. Chem., Int. Ed. 2004, 43, 1048. (c) Uma, R.;
Cre´visy, C.; Gre´e, R. Chem. ReV. 2003, 103, 27.
Figure 1. Proposed catalytic cycle of the rhodium-catalyzed isomerization
of R-arylpropargyl alcohols.
(2) Sa¨ıah, M. K. E.; Pellicciari, R. Tetrahedron Lett. 1995, 36, 4497.
(3) Several examples of propargyl alcohol isomerizations catalyzed by other
transition metals have been reported. Ruthenium catalysis: (a) Trost, B.
M.; Livingston, R. C. J. Am. Chem. Soc. 1995, 117, 9586. (b) Ma, D.;
Lu, X. J. Chem. Soc., Chem. Commun. 1989, 890. (c) Suzuki, T.;
Tokunaga, M.; Wakatsuki, Y. Tetrahedron Lett. 2002, 43, 7531. Iridium
catalysis: (d) Ma, D.; Lu, X. Tetrahedron Lett. 1989, 30, 2109. Palladium
catalysis: (e) Lu, X.; Ji, J.; Guo, C.; Shen, W. J. Organomet. Chem. 1992,
428, 259. (f) Guo, C.; Lu, X. Synlett 1992, 405. Rhenium catalysis: (g)
Narasaka, K.; Kusama, H.; Hayashi, Y. Tetrahedron 1992, 48, 2059. See
also: (h) Mamane, V.; Gress, T.; Krause, H.; Fu¨rstner, A. J. Am. Chem.
Soc. 2004, 126, 8654. (i) Harrak, Y.; Blaszykowski, C.; Bernard, M.;
Cariou, K.; Mainetti, E.; Mourie`s, V.; Dhimane, A.-L.; Fensterbank, L.;
Malacria, M. J. Am. Chem. Soc. 2004, 126, 8656.
RhH(PPh3)4 (eq 6), which gave indanone 2b in 45% yield (not
optimized), indicating the feasibility of the intermediacy of alkynone
A in Figure 1.9
We also carried out a series of competition experiments as
follows to gain more insights. (1) When a 1:1 mixture of 1b and 4
was subjected to the isomerization reaction, both 1b and 4 reacted
in the same rate (kH/kD ) 1.0),10,11 and (2) when a 1:1 mixture of
1b and 5 was employed, these reacted almost in the same rate with
each other as well (kH/kD ) 1.1).12 In addition, (3) the reaction
with monodeuterated substrate 7 provided the corresponding
indanone with 74% D at the ortho-carbon of the benzene ring,
showing that the reaction proceeded with kH/kD ) 2.8 (eq 7). These
results indicate that the 1,4-hydrogen shift (formation of B in Figure
1) is the turnover-limiting step of the catalytic cycle, and that there
is an irreversible step (presumably the step of conjugate hydro-
rhodation to intermediate A in Figure 1) prior to this 1,4-shift
because an intermolecular competition between 1b and 5 shows
almost no difference in reactivity with each other.
(4) In some cases, we have obtained partially desilylated indanones when
trimethylsilyl-substituted substrates are used.
(5) Due to the basic aqueous media, an H-D exchange at the R-position
occurs to lower the D-content at higher conversions.
(6) Treatment of a chlororhodium complex with aqueous KOH is known to
produce a hydroxorhodium species. For examples, see: (a) Grushin, V.
V.; Kuznetsov, V. F.; Bensimon, C.; Alper, H. Organometallics 1995,
14, 3927. (b) Uson, R.; Oro, L. A.; Cabeza, J. A. Inorg. Synth. 1985, 23,
126.
(7) For examples of a formation of an arylrhodium species involving a 1,4-
hydrogen shift, see: (a) Hayashi, T.; Inoue, K.; Taniguchi, N.; Ogasawara,
M. J. Am. Chem. Soc. 2001, 123, 9918. (b) Oguma, K.; Miura, M.; Satoh,
T.; Nomura, M. J. Am. Chem. Soc. 2000, 122, 10464.
(8) In an intermolecular system, we reported a mechanism involving a
formation of an oxa-π-allylrhodium complex by the addition of a
phenylrhodium species to an enone and its hydrolysis to give a hydroxo-
rhodium complex and a 1,4-addition product: Hayashi, T.; Takahashi,
M.; Takaya, Y.; Ogasawara, M. J. Am. Chem. Soc. 2002, 124, 5052.
(9) Under the catalytic reaction conditions, trans-1-phenyl-3-triethylsilyl-2-
propen-1-one (3b) does not produce indanone 2b, thereby eliminating the
possibility of a Nazarov-cyclization mechanism.
(10) Determined by 1H NMR at 6% conversion.
(11) For a recent example of an intermolecular kinetic isotope effect study
using 1H NMR analyses, see: Adams, C. S.; Legzdins, P.; McNeil, W. S.
Organometallics 2001, 20, 4939.
(12) Determined by 1H NMR at 4% conversion.
(13) (a) The use of bisphosphine ligands, such as dppb and dppf, is particularly
effective among those examined (dppe, messy reaction; dppp, low
reactivity). (b) The use of RhCl(bisphosphine)(PPh3) gives cleaner
reactions than the use of [RhCl(bisphosphine)]2 (which usually results in
the formation of rhodium-black).
Unfortunately, the catalytic isomerization conditions using
Wilkinson’s catalyst are not very effective for propargyl alcohols
bearing an alkyl group, instead of a silyl group on the alkyne, which
tend to give a complex mixture of multiple products. After
examining various catalysts,13 however, we were able to find that
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