Intramolecular additions of alcohols and carboxylic acids to inert olefins catalyzed by silver(I) triflate

Article abstract of DOI:10.1021/ol051065f

(Chemical Equation Presented) Intramolecular additions of hydroxyl or carboxyl groups to inert olefins catalyzed by simple silver(I) triflate are described. Good to excellent yields can be obtained for a range of substrates under relatively mild conditions. This reaction represents one of the simplest methods to construct cyclic ethers or lactones.

Full text of DOI:10.1021/ol051065f

ORGANIC
LETTERS
2005
Vol. 7, No. 21
4553-4556
Intramolecular Additions of Alcohols
and Carboxylic Acids to Inert Olefins
Catalyzed by Silver(I) Triflate
Cai-Guang Yang, Nicholas W. Reich, Zhangjie Shi,† and Chuan He*
Department of Chemistry, The UniVersity of Chicago, 5735 South Ellis AVenue,
Chicago, Illinois 60637
chuanhe@uchicago.edu
Received May 9, 2005 (Revised Manuscript Received September 2, 2005)
ABSTRACT
Intramolecular additions of hydroxyl or carboxyl groups to inert olefins catalyzed by simple silver(I) triflate are described. Good to excellent
yields can be obtained for a range of substrates under relatively mild conditions. This reaction represents one of the simplest methods to
construct cyclic ethers or lactones.
Silver-catalyzed reactions have recently begun to emerge as
important methods for organic synthesis.1 Silver(I) salts have
been used as Lewis acids to catalyze a variety of transforma-
tions2-9 and also exhibit interesting activity in catalyzing
oxidation reactions.10 Silver(I) is known to interact with
unsaturated hydrocarbons,11 while the use of silver(I) salts
to activate such substrates has been primarily limited to
allenes12 and alkynes13 so far. We have discovered that
(7) For a selected example on silylene transfer reactions, see: Cirakovic,
J.; Driver, T. G.; Woerpel, K. A. J. Am. Chem. Soc. 2002, 124, 9370-
9371.
† Current Address: Peking University, 202 Chengfu Road, Haidian
District, Beijing 100871, P. R. China.
(1) Yanagisawa, A. Lewis Acids in Organic Synthesis; Yamamoto, H.,
Ed.; Wiley-VCH: Weinheim, Germany, 2000; Vol. 2, Chapter 13.
(2) For selected examples on Aldol-type reactions, see: (a) Momiyama,
N.; Yamamoto, H. J. Am. Chem. Soc. 2004, 126, 5360-5361. (b) Hayashi,
T.; Uozumi, Y.; Yamazaki, A. Tetrahedron Lett. 1991, 32, 2799-2802.
(3) For selected examples on aldehyde allylation, see: (a) Yanagisawa,
A.; Nakashima, H.; Ishiba, A.; Yamamoto, H. J. Am. Chem. Soc. 1996,
118, 4723-4724. (b) Itami, K.; Kamei, T.; Mineno, M.; Yoshida, J. Chem.
Lett. 2002, 1084-1085.
(4) For selected examples on Diels-Alder reactions, see: (a) Josephsohn,
N. S.; Snapper, M. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2003, 125, 4018-
4019. (b) Patmore, N. J.; Hague, C.; Cotgreave, J. H.; Mahon, M. F.; Frost,
C. G.; Weller, A. S. Chem. Eur. J. 2002, 8, 2088-2098. (c) Loncaric, C.;
Manabe, K.; Kobayashi, S. AdV. Synth. Catal. 2003, 345, 475-477.
(5) For selected examples on Mannich-type reactions, see: (a) Joseph-
sohn, N. S.; Snapper, M. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2004, 126,
3734-3735. (b) Ferraris, D.; Young, B.; Dudding, T.; Lectka, T. J. Am.
Chem. Soc. 1998, 120, 4548-4549.
(8) For a review on the A3 coupling reaction, see: Wei, C.; Li, Z.; Li,
C.-J. Synlett. 2004, 1472-1483.
(9) For epoxide rearrangement, see: Wipf, P.; Methot, J.-L. Org. Lett.
1999, 1, 1253-1255.
(10) (a) Cui, Y.; He, C. J. Am. Chem. Soc. 2003, 125, 16202-16203.
(b) Cui, Y.; He, C. Angew. Chem., Int. Ed. 2004, 43, 4210-4212. (c) Dias,
H. V. R.; Browning, R. G.; Polach, S. A.; Diyabalanage, H. V. K.; Lovely,
C. J. J. Am. Chem. Soc. 2003, 125, 9270-9271. (d) Dias, H. V. R.;
Browning, R. G.; Richey, S. A.; Lovely, C. J. Organometallics 2004, 23,
1200-1202. (e) Burgess, K.; Lim, H.-J.; Porte, A. M.; Sulikowski, G. A.
Angew. Chem., Int. Ed. 1996, 35, 220-222.
(11) For reviews encompassing Ag(I)-alkene complexes, see: (a)
Bennett, M. A. Chem. ReV. 1962, 62, 611-652. (b) Quinn, H. W.; Tsai, J.
H. AdV. Inorg. Radiochem. 1969, 12, 217-373. (c) Beverwijk, C. D. M.;
Van der Kerk, G. J. M.; Leusink, A. J.; Noltes, J. G. Organomet. Chem.
ReV. 1970, 75, 215-280. (d) Herberhold, M. In Metal-π-Complexes;
Elsevier: Amsterdam, 1972; Vol. 2, pp 232-256.
(12) For a review, see: Bates, R. W.; Satcharoen, V. Chem. Soc. ReV.
2002, 31, 12-21.
(13) For selected examples, see: (a) Sweis, R. F.; Schramm, M. P.;
Kozmin, S. A. J. Am. Chem. Soc. 2004, 126, 7442-7443. (b) Marshall, J.
A.; Sehon, C. A. J. Org. Chem. 1995, 60, 5966-5968. (c) Huang, Q.;
Hunter, J. A.; Larock, R. C. J. Org. Chem. 2002, 67, 3437-3444. (d)
Harrison, T. J.; Dake, G. R. Org. Lett. 2004, 6, 5023-5026.
(6) For selected examples on [3 + 2] cycloaddition of azomethine ylides,
see: (a) Longmire, J. M.; Wang, B.; Zhang, X. J. Am. Chem. Soc. 2002,
124, 13400-13401. (b) Kno¨pfel, T. F.; Aschwanden, P.; Ichikawa, T.;
Watanabe, T.; Carreira, E. M. Angew. Chem., Int. Ed. 2004, 43, 5971-
5973. (c) Peddibhotla, S.; Tepe, J. J. J. Am. Chem. Soc. 2004, 126, 12776-
12777.
10.1021/ol051065f CCC: $30.25
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Published on Web 09/21/2005

silver(I) triflate is an excellent catalyst for intramolecular
hydroalkoxylation and hydroacyloxylation of inert olefins.
The hydoalkoxylation of olefins has traditionally been
mediated by stoichiometric amounts of toxic metal ions,
followed by reduction.14 Catalytic processes for such trans-
formations are limited, particularly for unactivated olefins.15
While palladium has been used to catalyze addition of
different nucleophiles to olefins, subsequent â-hydride
elimination reactions often occur to give the unsaturated
products.16 Recently, platinum,17 gold,18 tin,19 ruthenium,20
and iridium21 have been shown to act as good catalysts for
intramolecular and intermolecular hydroalkoxylation of un-
activated olefins. These metals are either toxic or relatively
expensive. We report here a simple and economic method
for mediating such a transformation.
obtained when triphenylphosphine was used (Table 1, entry
6). No product was observed with Zn(OTf)2 in a control
experiment. With Sc(OTf)3 as the Lewis acid, a 50% product
yield was obtained.
Further investigation into the scope of this reaction
indicated that good to excellent yields can be obtained with
a range of substrates, as shown in Table 2. The reaction gives
Table 2. Silver(I)-Catalyzed Intramolecular Addition of
Hydroxyl Groups to Olefinsa
The cyclization reaction of 2,2-diphenyl-4-hexene-1-ol 1
to afford the cyclic ethers 2 or 3 was used in our initial
screening of potential catalysts. We discovered that 5 mol
% of silver(I) triflate efficiently catalyzes this reaction. The
products were obtained in excellent yield (>95%) after 15
h at 83 °C in 1,2-dichloroethane (Table 1). The use of other
Table 1. Efficiency of Intramolecular Hydroalkoxylation of
Olefins Mediated by Selected Lewis Acids
entry
catalyst
CF3CO2Ag
C6H5CO2Ag
AgOTs
AgNO3
AgOTf
AgOTf/5.5 mol % of Ph3P
AgOTf/5.5 mol % of (C6F5)3P
Zn(OTf)2
yielda (%)
1
2
3
4
5
6
7
8
9
0
0
0
0
>95 (10:1)
<10
90 (10:1)
0
Sc(OTf)3
50
1
a Yield based on H NMR using an internal standard.
silver salts failed to yield the desired products as revealed
1
by H NMR (Table 1, entries 1-4). The reaction also
occurred in the presence of an electron-deficient ligand
(Table 1, entry 7), whereas less than 10% conversion was
(14) Larock, R. C.; Leong, W. W. ComprehensiVe Organic Synthesis;
Trost, B. M., Fleming, I., Eds.; Pergamon Press: New York, 1991; Vol. 4.
(15) For a review, see: Beller, M.; Seayad, J.; Tillack, A.; Jiao, H. Angew.
Chem., Int. Ed. 2004, 43, 3368-3398.
a Reactions were conducted with 1-2 mmol of substrate and 5 mol %
of AgOTf in 4-6 mL of dichloroethane at 83 °C for 15 h. b Isolated yields
are reported here. c 1H NMR yields based on an internal standard. d Ratio
based on isolated yields. e When 5 mol % of HOTf was used as catalyst,
the isolated yield was <10%. f Reaction completed in 36 h.
(16) For selected reviews, see: (a) Stahl, S. S. Angew. Chem., Int. Ed.
2004, 43, 3400-3420. (b) Hosokawa, T.; Murahashi, S.-I. Heterocycles
1992, 33, 1079-1100.
(17) Qian, H.; Han, X.; Widenhoefer, R. A. J. Am. Chem. Soc. 2004,
126, 9536-9537.
(18) Yang, C.-G.; He, C. J. Am. Chem. Soc. 2005, 127, 6966-6967.
(19) Coulombel, L.; Favier, I.; Dunach, E. Chem. Commun. 2005, 2286-
2288.
(20) Oe, Y.; Ohta, T.; Ito, Y. Synlett 2005, 179-181.
(21) Grant, V. H.; Liu, B. Tetrahedron Lett. 2005, 46, 1237-1239.
preferentially the Markovnikov ethers as expected. Similar
regioselectivity has been observed for the platinum-based
system.17 The reaction of terminal γ-hydroxyl alkenes leads
exclusively to the formation of the 5-exo cyclization products
4554
Org. Lett., Vol. 7, No. 21, 2005

in good to excellent yields (Table 2, entries 1, 4, and 5).
The use of a terminal monosubstituted olefin gave a mixture
of the 5-exo and 6-endo cyclic products with the 5-exo
product significantly favored (Table 2, entry 3). However,
the 6-endo cyclic ethers were found to be the sole products
for terminal di-substituted alkenes (Table 2, entries 2 and
13) and a γ-hydroxyl alkene with a phenyl substitution at
the terminus (Table 2, entry 14). This reaction is general for
alkenes bearing various substitutions at the R, â and γ-carbon
atoms and tolerates different functional groups. The silver(I)
triflate-catalyzed hydroalkoxylation is also applicable to the
synthesis of fused- and spirobicyclic ethers in good yields
(Table 2, entries 6 and 12).
Table 4. Silver(I)-Catalyzed Intramolecular Addition of
Carboxylic Acids to Olefinsa
Expanding our investigation to carboxylic acids, we again
found that silver(I) triflate was the optimal catalyst while
other silver or triflate salts failed to catalyze the reaction,
with the exception of scandium(III) triflate, though at lower
yields than silver triflate (Table 3). Similarly, the efficiency
Table 3. Efficiency of Intramolecular Additions of Carboxylic
Acids to Olefinsa
entry
catalyst
yielda (%)
1
2
3
4
5
6
7
8
CF3CO2Ag
C6H5CO2Ag
AgOTs
AgF
AgNO3
AgOTf
Zn(OTf)2
Sc(OTf)3
0
0
0
0
0
>95
0
70
a Yield based on H NMR using an internal standard.
1
a Reactions were conducted under the conditions described in Table 2.
b The isolated yields are reported here. c Ratio based on isolated yield.
d Reaction completed in 36 h.
and regioselectivity of hydroacyloxylation is also sensitive
to terminal olefinic substitution (Table 4). Testing our
reaction conditions on hex-5-enoic acid resulted in the
predominant formation of the six-membered ring (Table 4,
entry 9), along with small amounts of the five-membered
ring. The formation of the five-membered ring presumably
comes from olefin migration catalyzed by silver(I); similar
chemistry has been observed recently with gold(I) as well.18
The strictly cis relation of the substitutions on the two
bridgehead carbons can be always seen in the formation of
the fused ring systems for substrates containing either an
alcohol (Table 2, entry 12) or a carboxylic acid (Table 4,
entry 8) as the nucleophiles.
formation of the product and regeneration of the silver(I)
catalyst.
We monitored the intramolecular silver(I)-catalyzed hy-
1
droalkoxylation of olefin 1 with H NMR spectroscopy.22
Scheme 1. Proposed Mechanism for Hydroalkoxylation
Our proposed mechanism for the silver(I) triflate-mediated
hydroalkoxylation or hydroacyloxylation is shown in Scheme
1. The silver(I) ion binds and activates the double bond,
which is then attacked by the oxygen-nucleophile on the
opposite face. This affords an intermediate with the newly
formed carbon-oxygen bond positioned trans to the silver-
carbon bond. Subsequent proton-transfer results in the
Org. Lett., Vol. 7, No. 21, 2005
4555

Addition of silver(I) triflate to an equimolar solution of olefin
1 in methylene chloride-d2 results in significant lower field
shifts of the alkene proton signals in the 1H NMR spectrum
at room temperature. The similar signal shifts were also
observed at room temperature in 1,2-dichloroethane-d4 while
further shifts occur upon heating to 80 °C. The reaction was
Scheme 2. Investigation of Stereochemistry
1
followed by H NMR at 80 °C. A smooth formation of the
desired product and a steady decrease of the olefin signals
were observed. These results indicate that the silver(I) ion
interacts with the olefin to form a π-complex11 during the
course of the reaction. Potential release of triflic acid via
metathesis of the silver(I) ion with the OH bond of the
substrate is not likely the mechanism. In fact, Zn(OTf)2 and
Sc(OTf)3 can interact with alcohols more strongly than
silver(I). Yet, Zn(OTf)2 is inactive and Sc(OTf)3 gives a
lower convertion than silver(I) triflate (Table 1). The activity
of the silver(I) ion can be tuned with ligands (entries 6 and
7, Table 1) and the fact that some acid-sensitive groups can
be tolerated (entries 7 and 9, Table 2) further support this
notion. In fact, 5% HOTf was used as a control for a TIPS
protected substrate (entry 9, Table 2) and less than 10% of
the desired product (with TIPS on) was isolated under the
same reaction conditions.
Two additional substrates (6 and 9 in Scheme 2) were
prepared to probe the stereoselectivity of the silver(I)-
catalyzed reaction. Products 7 and 8 were isolated in a 2:1
ratio under the standard reaction conditions with substrate
6. Similarly, reaction with 9 was carried out to give 10 (36%)
and 11 (52%). The substituents on the bridgehead carbons
of products 7 and 10 have a strictly cis geometry to the
neighboring methyl groups.23 This observation indicates that
the nucleophile attacks the face of the double-bond opposite
to which silver is bound in the intermediate state, supporting
our proposed mechanism.
In summary, we present here the silver(I)-catalyzed
intramolecular addition of hydroxyl or carboxyl groups to
unactivated olefins to form cyclic ethers or lactones, respec-
tively. The use of silver is economic as compared to
stoichiometric amounts of toxic metal ions or catalytic
amounts of expensive transition metal ions employed previ-
ously. This procedure may also be expanded to other types
of additions to simple olefins.
Acknowledgment. This research was supported by the
University of Chicago. We acknowledge the donors of the
American Chemical Society Petroleum Fund for support of
this research (PRF 38848-G3). This research is also funded
by a Research Innovation Award (RI1179) from Research
Corporation and an Alfred P. Sloan Research Fellowship to
C.H.
(22) For details, see Figures S1-S13 in the Supporting Information.
(23) The assignment of the stereochemistry of compound 7 is based on
the 2D NMR experiments (for details, see the Supporting Information).
Similarly, we determine the stereochemistry of compound 10 by comparison
with compound 7. And also see: Doyle, M. P.; Kalinin, A. V.; Ene, D. G.
J. Am. Chem. Soc. 1996, 118, 8837-8846.
Supporting Information Available: Experimental details
and Figure S1-S13. This material is available free of charge
via the Internet at http://pubs.acs.org.
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Org. Lett., Vol. 7, No. 21, 2005