possibility of generating these carbonyl ylide species using
other transition metal complexes. In this paper is described
the result of such examination, that is, generation of
platinum-containing carbonyl ylide species by the reaction
of o-alkynylbenzoates or benzothioates with a catalytic
Table 1. Screening of the Reaction Conditions
4
amount of PtCl2 and their use for the concise synthesis of
1-acyl-4-alkoxy- or 1-acyl-4-alkylsulfanylnaphthalenes by the
reaction with vinyl ethers.
entry
catalyst
solvent
time
yield/%
In the first place, we examined the above reactions
employing PtCl2 as a catalyst instead of the tungsten
complex. The reaction of o-ethynylbenzaldehyde or o-
ethynylacetophenone with butyl vinyl ether in the presence
of a catalytic amount of PtCl2 resulted in a complex mixture,
and none of the addition product was obtained. On the other
hand, when a mixture of isopropyl o-ethynylbenzoate 1a and
butyl vinyl ether was treated with PtCl2 (10 mol %) in THF,
the starting material was consumed within several hours at
room temperature,5 and purification of the crude products
revealed that 4-isopropoxynaphthalene-1-carbaldehyde 2a
was obtained in moderate yield instead of the polycyclic
compound 3 (Scheme 2). As formation of the naphthalene
1
2
3
4
5a
6
7
PtCl2
PtCl2
PtCl2
PtCl2
PtCl2
PtBr2
AuCl3
CH3CN
CH2Cl2
Et2O
toluene
toluene
toluene
toluene
2 days
16 h
9 h
6 h
10 h
47
71
84
86
91
47
10
2 days
2 days
a MS4A was added.
was carried out in toluene in the presence of molecular sieves
4A, the yield of 2a was further improved to 91% (entry 5).
Some other transition-metal compounds such as PtBr2 and
AuCl3 were also examined under the conditions of entry 4;
however, the naphthalene 2a was obtained in low yield and
PtCl2 was found to be the most suitable catalyst for this
reaction.
Scheme 2
Since the optimal reaction conditions had become clear,
we then investigated generality of the reaction using various
o-alkynylbenzoic acid derivatives, and the results were
summarized in Table 2. As for the ester functionality, alkoxy,
Table 2. Reaction of Various o-Alkynylbenzoates and
o-Alkynylbenzothioate
derivative 2a was rather unexpected, we decided to examine
this platinum(II)-catalyzed naphthalene synthesis in more
detail.
To improve efficiency of this reaction, we first investigated
the above reaction in various solvents (Table 1). Although
the use of acetonitrile did not improve the yield of 2a (entry
1), the reaction in dichloromethane, ether, and toluene
smoothly proceeded to afford 2a in 71, 84, and 86% yield,
respectively (entries 2-4). In addition, when the reaction
entry
XR1
R2
time
yield/% ratio 2/4
1
2
3
4
5
6
7
8
9a
O-i-Pr
OMe
OPh
O-p-ClPh
OCH2Ph
SC8H17
NEt2
O-i-Pr
O-i-Pr
H
H
H
H
H
H
H
n-Pr
Ph
1a
1b
1c
1d
1e
1f
1g
1h
1i
10 h
12 h
10 h
11 h
8 h
9 h
9 h
3 days
5 days
91
84
90
86
77
60
-
100:0
61:39
51:49
50:50
56:44
65:35
(3) For formation of metal-containing ylides, see: (a) Padwa, A.;
Gasdaska, J. R. J. Am. Chem. Soc. 1986, 108, 1104. For a recent related
example, see: (b) Miki, K.; Nishino, F.; Ohe, K.; Uemura, S. J. Am. Chem.
Soc. 2002, 124, 5260.
(4) (a) Mendez, M.; Mamame, V.; Fu¨rstner, A. Chemtracts - Org. Chem.
2003, 16, 397. (b) Chatani, N.; Morimoto, T.; Muto, T.; Murai, S. J. Am.
Chem. Soc. 1994, 116, 6049. (c) Chatani, N.; Furukawa, N.; Sakurai, H.;
Murai, S. Organometallics 1996, 15, 901. (d) Chatani, N.; Inoue, H.; Ikeda,
T.; Murai, S. J. Org. Chem. 2000, 65, 4913. (e) Ferna´ndez-Rivas, C.;
Me´ndez, M.; Echavarren, A. M. J. Am. Chem. Soc. 2000, 122, 1221. (f)
Nevado, C.; Ca´rdenas, D. J.; Echavarren, A. M. Chem. Eur. J. 2003, 9,
2627. (g) Mainetti, E.; Mourie`s, V.; Fensterbank, L.; Malacria, M.; Marco-
Contelles, J. Angew. Chem., Int. Ed. 2002, 41, 2132. (h) Fu¨rstner, A.; Stelzer,
F.; Szillat, H. J. Am. Chem. Soc. 2001, 123, 11863. (i) Oi, S.; Tsukamoto,
I.; Miyano, S.; Inoue, Y. Organometallics 2001, 20, 3704. For recent
examples of the use of PtCl4, see: (j) Pastine, S. J.; Youn, S. O.; Sames,
D. Tetrahedron 2003, 59, 8859. (k) Baidossi, W.; Schumann, H.; Blum, J.
Tetrahedron 1996, 52, 8349.
89
64
100:0
100:0
a The reaction was performed in the presence of 30 mol % of PtCl2.
aryloxy, and alkylsulfanyl groups were applicable and the
corresponding naphthalenes were obtained in high yield
(entries 1-6). In particular, formation of n-octylsulfanyl-
substituted naphthalene 2f is noteworthy as it is not neces-
sarily easy to introduce alkylsulfanyl group onto naphthalene.
On the contrary, the reaction of an amide derivative 1g did
not proceed and the starting material was recovered. Except
(5) In marked contrast with the platinum catalyzed reaction, treatment
of isopropyl o-ethynylbenzoate 1a and butyl vinyl ether with a catalytic
amount of preformed W(CO)5(thf) did not produce the expected adduct 3
at all, and the starting material 1a remained intact.
606
Org. Lett., Vol. 6, No. 4, 2004