C O M M U N I C A T I O N S
Table 1. Pt(II) and Cu(I)-Catalyzed Rearrangements of Propargyl
Derivatives 1
lective (the ethoxyalkyne unit reacts in preference over the
phenylalkyne unit; see diyne 3). Studies to accomplish new
cycloisomerization processes and to get insight into the mechanism
are ongoing.
Acknowledgment. Financial support for this work is acknowl-
edged (CTQ2004-08077 and IB 05-136). L.R. thanks the Ministerio
de Educacio´n y Ciencia for a predoctoral fellowship.
Supporting Information Available: Experimental procedures and
spectral and analytical data for compounds 2, 4, and 5. This material
yield (%)a
entry
R1
R2
2
(conditions)
Z:Eb
1
Ph
Me
Me
Me
Me
2a
81 (A)
84 (B)
71 (A)
58 (B)
75 (A)
50 (B)
70 (A)
82 (B)
79 (A)
88 (B)d
60 (B)
30 (A)
51 (A)
60 (A)
70 (B)
68 (A)
69 (A)
only Z
10:90
50:50
50:50
only Z
only E
only Z
only E
only Z
only E
20:80
75:25
70:30
75:25
only E
-
References
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2c
3
p-MeOC6H4
p-NO2C6H4
1-naphthyl
2b
2c
2d
4
5
6
7
8
9
2-furyl
Me
Me
Me
Me
Ph
2e
2f
2g
2h
2i
iPr
(E)-Ph-CHdCH
CH2dCH(CH2)3
Ph
Ph
10
CHdCH2
2j
11
12
Ph
Ph
OEt
OMe
2k
2l
only Z
a Yield of isolated product after column chromatography. b Estimated
by 1H NMR (400 MHz) of the reaction crude. The individual isomers were
separated in most cases by column chromatography (see Supporting
Information). c See ref 10. d Yield referred to unpurified product as
chromatographic purification leads mostly to decomposition.
(6) Wang, S.; Zhang, L. J. Am. Chem. Soc. 2006, 128, 8414.
(7) (a) Bhanu Prasad, B. A.; Yoshimoto, F. K.; Sarpong, R. J. Am. Chem.
Soc. 2005, 127, 12468. (b) Pujanauski, B. G.; Bhanu Prasad, B. A.;
Sarpong, R. J. Am. Chem. Soc. 2006, 128, 6786.
Scheme 3. Pt(II)- and Cu(I)-Catalyzed Transformations of Diyne 3
(8) (a) For the gold(III)-catalyzed Meyer-Schuster rearrangement of propargyl
alcohols derived from ethoxyacetylene, see: Engel, D. A.; Dudley, G. B.
Org. Lett. 2006, 8, 4027. (b) Lopez, S. S.; Engel, D. A.; Dudley, G. B.
Synlett 2007, 949. (c) For Au- and Pt-catalyzed cycloisomerization of
1-siloxy-1-yne-5-enes, see: Sun, J.; Conley, M. P.; Zhang, L.; Kozmin,
S. A. J. Am. Chem. Soc. 2006, 128, 9705.
(9) The selective preparation of such systems by the Knoevenagel reaction is
associated with great problems; see: (a) Tietze, L. F.; Beifus, U. In
ComprehensiVe Organic Synthesis; Trost, B. M., Ed.; Pergamon Press:
Oxford, 1991; Vol. 2, p 341. (b) See also ref 6.
(10) We have observed that the individual alkene adducts (Z)- and (E)-2b,
having electron-withdrawing and electron-donating substituents in con-
jugation, isomerize into a 1:1 E/Z mixture in the presence of either Pt(II)
or Cu(I) catalyst.
(11) Benzoylfuran 6 resulting from oxidation of carbene I is formed in 42%
yield when a solution of 3 in THF was stirred in air in the presence of
CuCl (5 mol %). For metal-catalyzed cyclization of conjugated ynenones
Scheme 4. Proposed Mechanism for the Formation of (E)- and
(Z)-2
generating metal furan carbene, see: Miki, K.; Yokoi, T.; Nishino, F.;
Kato, Y.; Washitake, Y.; Ohe, K.; Uemura, S. J. Org. Chem. 2004, 69,
1557.
(12) For the easy dimerization of Cu(I) carbene complexes, see: Barluenga,
J.; Lo´pez, L. A.; Lo¨ber, O.; Toma´s, M.; Garc´ıa-Granda, S.; AÄ lvarez-Ru´a,
C.; Borge, J. Angew. Chem., Int. Ed. 2001, 40, 3392.
(13) (a) The ability of PtCl2 for coordination to oxygen has been recently
observed in the cyclization of haloallenylketones: Sromek, A. W.; Rubina,
M.; Gevorgyan, V. J. Am. Chem. Soc. 2005, 127, 10500. (b) For
spectroscopic evidence for Pt(II)-carbonyl oxygen interaction, see:
Fu¨rstner, A.; Voigtla¨nder, D.; Schrader, W.; Giebel, D.; Reetz, M. T. Org.
Lett. 2001, 3, 417.
(14) For recent notable exceptions, see: (a) Fehr, C.; Galindo, J. Angew. Chem.
2006, 118, 2967; Angew. Chem., Int. Ed. 2006, 45, 2901 (propargylic
acetates). (b) Fehr, C.; Farris, I.; Sommer, H. Org. Lett. 2006, 8, 1839
(propargyl alcohols).
the effectiveness of Cu(I), which are rarely used in metal-catalyzed
cycloisomerization reactions, are noteworthy.14 In terms of mecha-
nistic and synthetic implications, it is demonstrated that the
rearrangement of alkoxy-substituted substrates is totally regiose-
lective (1,3- in preference to 1,2-acyloxy migration) and chemose-
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