residue was purified on silical column (hexane–AcOEt 9 : 1) to give
aldehyde 2 (181 mg, 1.07 mmol) in 80% yield as a colorless liquid. 1H
NMR (400 MHz, CDCl3): d 10.07 (s, 1H), 8.13 (s, 1H), 8.00–7.95 (m, 2H),
7.75 (s, 1H), 7.64 (t, 1H, J = 7.6 Hz), 7.55 (t, 1H, J = 7.6 Hz), 2.68 (s, 3H);
13C NMR (100 MHz, CDCl3): d 192.3, 135.7, 133.6, 133.2 6 2, 132.6,
130.1, 128.9, 126.6, 124.3, 12.7, 19.2. IR (neat) n 2978, 1650 cm21. HRMS:
calc. for C12H10O ([M + H]+) 170.0732, found 170.0729.
The metal–naphthylidene intermediates in the preceding oxida-
tive cyclizations are considered to be kinetically stable because of
the lack of a Cb-alkyl hydrogen for a competitive 1,2-hydrogen
shift.10 We therefore studied oxidative cyclization of alcohol 4 with
PEt3AuCl/H2O2 in hot dichloroethane (70 uC, 6 h), which afforded
desired ketone 31 with a yield up to 83% whereas olefin product 5
(78%) was dominant over ketone 31 (6%) in the PtCl2/H2O
catalysis, as depicted in Table 3 (entry 1). For this Au-catalyzed
cyclization, the preference for the oxygenation reaction is
manifested with additional examples shown in Table 3. We
prepared also benzyl alcohols 26–30 with alternative alkynyl
CH2R (R = n-propyl or n-heptyl) substituents as well as phenyl X,
Y groups (entries 2–6); PEt3AuCl/H2O2 effects the efficient
transformation of these alcohols into the corresponding ketones
32–36 (yields . 80%), with olefin byproducts 38 and 39 (,4%)
given in two examples in small proportions. In contrast, PtCl2
failed to give desired ketones products significantly (,7%) because
a rapid 1,2-hydrogen shift reaction gave olefin products 37–41 in
large proportions (68–85%). In the PtCl2 case, when we attempted
the oxidative cyclization of alcohol 4 with H2O2 rather than H2O
in DCE (70 uC, 8 h), we obtained ketone 31 and olefin 5 in 52 and
4% yields respectively. This information reveals that the poor
nucleophilicity of water accounts for its preference for formation
of olefin 5 in the PtCl2-catalysis.
1 For reviews, see: (a) L. Zhang, S. Sun and S. Kozmin, Adv. Synth.
Catal., 2006, 348, 2271; (b) S. M. Ma, S. Yu and Z. Gu, Angew. Chem.,
Int. Ed., 2006, 45, 200; (c) C. Bruneau, Angew. Chem., Int. Ed., 2005, 44,
2328; (d) A. S. K. Hashmi, Angew. Chem., Int. Ed., 2005, 44, 6990; (e)
A. M. Echavarren and C. Nevado, Chem. Soc. Rev., 2004, 33, 431.
2 Selected examples: (a) Y. Harrak, C. Blaszykowski, M. Bernard,
K. Cariou, E. Mainetti, V. Mourie´s, A.-L. Dhimane, L. Fensterbank
and M. Malacria, J. Am. Chem. Soc., 2004, 126, 8656; (b) V. Mamane,
T. Gress, H. Krause and A. Fu¨rstner, J. Am. Chem. Soc., 2004, 126,
8654; (c) M. J. Johansson, D. J. Gorin, S. T. Staben and D. F. Toste,
J. Am. Chem. Soc., 2005, 127, 19002; (d) M. R. Luzung, J. P. Markham
and J. F. Toste, J. Am. Chem. Soc., 2004, 126, 10858; (e) N. Chatani,
K. Kataoka and S. Murai, J. Am. Chem. Soc., 1998, 120, 9104; (f)
A. Fu¨rstner and P. Hannen, Chem. Commun., 2004, 2546.
3 (a) B. A. Bhanu Prasad, F. K. Yoshimoto and R. Sarpong, J. Am.
Chem. Soc., 2005, 127, 12468; (b) B. P. Taduri, Y.-F. Ran, C.-W. Huang
and R.-S. Liu, Org. Lett., 2006, 8, 883.
4 Selected recent examples, see: (a) C. Nieto-Oberhuber, M. P. Mun˜oz,
E. Bun˜uel, C. Nevado, D. J. Ca´rdenas and A. M. Echavarren, Angew.
Chem., Int. Ed., 2004, 43, 2402; (b) H. Kuwasa, H. Funami, J. Takaya
and N. Iwasawa, Org. Lett., 2004, 6, 605; (c) C. Nieto-Oberhuber,
ˇ
S. Lope´z, E. Jime´nez-Nu´nez and A. M. Echavarren, Chem. Eur. J.,
2006, 12, 5916.
Despite its lower efficiency, the use of water in PtCl2/CO
catalysis is economically and environmentally interesting because
useful H2 is also produced. To examine the feasibility of this
process, we have calculated the enthalpy change for the water-
oxygenation of platinum–benzylidene species using the Gaussian
98 program.11 The DH value is more favorable for trans-
PhCHLPtCl2(H2O) (DH = 21.14 kcal mol21) than its cis isomer
(DH = +12.59 kcal mol21).
5 For oxidation of metal–carbenes with decomposition of metal
complexes, see selected examples: (a) J. Barluenga, P. L. Bernad,
J. M. Concellon, A. Pinera-Nicolas and S. Carcia-Granda, J. Org.
Chem., 1997, 62, 6870; (b) A. G. Barrett, J. Mortier, M. Sabat and
M. A. Sturgess, Organometallics, 1988, 7, 2553; (c) W.-K. Liang,
W.-T. Li, S.-M. Peng, S.-L. Wang and R.-S. Liu, J. Am. Chem. Soc.,
1997, 119, 4404; (d) G. Erker and F. Sosna, Organometallics, 1990, 9,
1949; (e) P. Quayle, S. Rahman and E. L. M. Ward, Tetrahedron Lett.,
1994, 35, 3801; (f) K. Miki, T. Yokoi, F. Nishino, K. Ohe and
S. Uemura, J. Organomet. Chem., 2002, 645, 228.
6 B. M. Trost and Y. H. Rhee, J. Am. Chem. Soc., 1999, 121, 11680.
7 S. Shin, A. K. Gupta, C. Y. Rhim and C. H. Oh, Chem. Commun.,
2005, 4429.
8 For PtCl2/CO catalyst, see: (a) A. Fu¨rstner, P. W. Davies and T. Gress,
J. Am. Chem. Soc., 2005, 127, 8244; (b) A. Fu¨rstner and C. A¨ıssa, J. Am.
Chem. Soc., 2006, 128, 6306; (c) A. Fu¨rstner and P. W. Davies, J. Am.
Chem. Soc., 2005, 127, 15024.
9 For a tandem heteroaromatization and cyclopropanation catalyzed by
transition metals complexes, see: (a) K. Miki, F. Nishino, K. Ohe and
S. Uemura, J. Am. Chem. Soc., 2002, 124, 5260; (b) F. Nishino, K. Miki,
Y. Kato, K. Ohe and S. Uemura, Org. Lett., 2003, 5, 2615.
10 W. Kirmse, Carbene Chemistry, Academic Press, New York, 2nd edn,
1971.
In summary, we have examined a new oxidative cyclization12 of
2-ethenyl-1-(prop-29-yn-19-ol)benzenes to give naphthyl aldehydes
and ketones using PtCl2/CO/H2O13 and PEt3AuCl/H2O2 sys-
tems;14 the resulting metal–naphthylidene intermediates in such
cyclizations were identified and oxygenated by water and H2O2,
respectively. The Au-catalyst is far superior to platinum system for
the production of the desired ketones and aldehydes from diverse
alcohol substrates. Further use of this approach to oxidative
cyclization of 1,5- and 1,6-enynes are under current investigation.
11 See ESI for detailed calculation procedures{.
12 For oxidative cleavage of C–C multiple bonds using Au catalysts and
oxidants, see: (a) Y. Liu, F. Song and S. Guo, J. Am. Chem. Soc., 2006,
128, 11332; (b) D. Xing, B. Guan, G. Cai, Z. Fang, L. Yang and Z. Shi,
Org. Lett., 2006, 8, 693.
13 The experimental procedure for measurement of the evolved H2 in the
PtCl2/CO/H2O system is provided in ESI{.
14 PtCl2/CO/H2O did not catalyze the oxidation of alcohol 42 to aldehyde
2 under air or nitrogen. However, we obtained aldehyde 2 in 15% yield
with a 63% recovery of unreacted 42 in the PEt3AuCl/H2O2 system. We
cannot exclude the possibility that some portions of aldehyde products
arise from their alcohol precursors via decomposition of Au–carbenoid
species with water.
Notes and references
{ Representative procedure for AuClEt3 cyclization: To a solution of
alcohol 1 (230 mg, 1.33 mmol) and AuClEt3 (21.5 mg, 0.066 mmol) in
DCE (5 ml) was added H2O2 (136 mg, 4 mmol). After this reaction mixture
was stirred at 70 uC for 6 h, water (7 ml) was added to quench the reaction.
The mixture was extracted with ether twice. The combined extracts were
dried over MgSO4. After removal of solvent under reduced pressure, the
2532 | Chem. Commun., 2007, 2530–2532
This journal is ß The Royal Society of Chemistry 2007