ium(I). Then, 1,2-addition across the carbon-carbon triple
7
bond occurs to give the alkenylrhodium(I) intermediate A.
Table 1. Rhodium-Catalyzed Synthesis of Substituted
Intramolecular nucleophilic addition to the cyano group in
a 5-exo-dig mode follows to give intermediate B, which was
hydrolyzed to 3a, ammonia, and hydroxorhodium(I). Al-
though similar indanone skeletons can be synthesized by a
related [3 + 2] annulation reaction of 2-iodobenzonitrile with
alkynes catalyzed by palladium, relatively low yields have
been reported for internal alkynes other than diphenyl-
a
Indenones or Indanones with 2-Cyanophenylboronic Acid (2)
6
c
acetylene.
The results of the [3 + 2] annulation reaction with other
alkynes 1b-1f are summarized in Table 1. Diphenylacety-
lene (1b) afforded 2,3-diphenylindenone (3b) in 76% yield
(entry 1). Unsymmetrically disubstituted alkynes 1c-1f gave
moderate to good regioselectivities. Of note was that the
major regioisomers obtained with 1e and 1f were opposite
6a,c
to those given by the related palladium-catalyzed reactions.
Terminal alkynes, such as phenylacetylene and 1-octyne,
failed to undergo the annulation reaction. Although ordinary
alkenes did not react either, strained bicyclic alkenes 1g and
1h did participate in the [3 + 2] annulation reaction to afford
the corresponding exo-adducts 3g and 3h, respectively. In
8
addition, the use of chiral diene ligand 5, developed by
Carreira et al., led to the formation of indanone 3h in 80%
ee (eq 1).
To assess the reactivity of the cyano group relative to other
electrophilic functional groups, 2-(methoxycarbonyl)phenyl-
boronic acid (4) was examined under similar reaction
2
conditions. Direct hydrolysis of 4 to methyl benzoate mainly
occurred, with only 5% of 3a observed after 2 days along
with a small amount of 6 (9%), likely resulting from
hydrolysis of the initial 1,2-adduct (eq 2). In the case of
a
The reaction was carried out with 1 (0.35 mmol) and 2 (1.40 mmol) in
the presence of [Rh(OH)(cod)]2 (0.035 mmol of Rh) at 100 °C in dioxane/
H2O (3.5 mL/88 µL) for 2 days. Isolated yields. c Regioisomers ratio. The
major isomer is designated.
b
significantly different results obtained with 2 and 4 demon-
strate the greatly increased reactivity of cyano groups relative
to alkoxycarbonyl groups in intramolecular reactions with
organorhodium(I) species.
Finally, ethyl 2-hexynoate (7) was reacted with 2 under
similar reaction conditions. To our surprise, seven-membered
ring benzotropone derivative 8 was obtained as the major
product (64%) instead of the five-membered ring indenone
2
-cyanophenylboronic acid (2), the product resulting from
hydrolysis of A in Scheme 1 was not detected. The
(5) For rhodium-catalyzed annulation using arylboronate esters bearing
electron-deficient alkenes, see: (a) Lautens, M.; Mancuso, J. J. Org. Chem.
9
derivative (Scheme 2). The alkenylrhodium(I) intermediate
2
004, 69, 3478. (b) Lautens, M.; Marquardt, T. J. Org. Chem. 2004, 69,
4
607.
(
6) For synthetic methods of 2,3-disubstiuted indenone from alkynes,
see: (a) Larock, R. C.; Doty, M. J.; Cacchi, S. J. Org. Chem. 1993, 58,
579. (b) Kokubo, K.; Matsumasa, K.; Miura, M.; Nomura, M. J. Org.
(7) For 1,2-addition of arylrhodium(I) onto an internal alkyne, see: (a)
Hayashi, T.; Inoue, K.; Taniguchi, N.; Ogasawara, M. J. Am. Chem. Soc.
2001, 123, 9918. (b) Lautens, M.; Yoshida, M. Org. Lett. 2002, 4, 123.
(8) Defieber, C.; Paquin, J.-F.; Serna, S.; Carreira, E. M. Org. Lett. 2004,
6, 3873. See also: Otomaru, Y.; Okamoto, K.; Shintani, R.; Hayashi. T. J.
Org. Chem. 2005, 70, 2503 and references therein.
4
Chem. 1996, 61, 6941. (c) Pletnev, A. A.; Tian, Q.; Larock, R. C. J. Org.
Chem. 2002, 67, 9276. (d) Vicente, J.; Abad, J.-A.; L o´ pez-Pel a´ ez, B.;
Mart ´ı nez-Viviente, E. Organometallics 2002, 21, 58.
3340
Org. Lett., Vol. 7, No. 15, 2005
Miura, Tomoya
