Intriguing formal [2+3] cycloaddition promoted by a hypervalent iodine reagent

Article abstract of DOI:10.1016/j.tet.2008.05.114

Treatment of various substituted phenols in the presence of iodobenzene diacetate, perfluorinated alcohols and furan, allylsilanes or cyclic enol ethers promotes an oxidative annulation process in moderate to useful yields. In only one step, this method p

Full text of DOI:10.1016/j.tet.2008.05.114

Tetrahedron 64 (2008) 7537–7544
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Intriguing formal [2þ3] cycloaddition promoted by a hypervalent
iodine reagent
*
´
´
´
Didier Berard, Marc-Andre Giroux, Leanne Racicot, Cyrille Sabot, Sylvain Canesi
`
´
´
´
Laboratoire de Me´thodologie et Synthe`se de Produits Naturels, Universite´ du Que´bec a Montreal, C.P. 8888, Succ. Centre-Ville, Montreal, Quebec, H3C 3P8, Canada
a r t i c l e i n f o
a b s t r a c t
Article history:
Treatment of various substituted phenols in the presence of iodobenzene diacetate, perfluorinated al-
cohols and furan, allylsilanes or cyclic enol ethers promotes an oxidative annulation process in moderate
to useful yields. In only one step, this method produces different heterocyclic rings such as dihy-
drofuranobenzofurans, tetrahydrofuranobenzofurans, tetrahydropyranofurans, and dihydrobenzofurans.
Ó 2008 Elsevier Ltd. All rights reserved.
Received 28 March 2008
Received in revised form 21 May 2008
Accepted 28 May 2008
Available online 16 June 2008
1. Introduction
a position adjacent to the carbonyl group (pathway a), resulting in
the formation of products 8, albeit in low yield (Scheme 2).
The potential of iodobenzene diacetate (DIB), an environmen-
tally benign and inexpensive reagent, is now well known.1 This
reagent promotes noteworthy oxidative transformations of phenol2
and aniline3 derivatives, in a manner consistent with the recent
requirements for green chemical processes. As observed by Kita,4
DIB reactions generally occur best in solvents such as tri-
fluoroethanol (TFE) or hexafluoroisopropanol (HFIP).5 Under these
conditions, oxidative attack of phenols in the presence of un-
hindered heteronucleophiles6 tends to proceed through pathway
b to afford compound 5. The species 4 would arise through DIB
activation of the phenol 1, Scheme 1.
O
OH
S
S
O
S
- H
a
17% in TFE
23% in HFIP
8
4b
7
Scheme 2.
Although compound 8 is obtained in low yield, this result opens
a new opportunity in organic synthesis. As a matter of fact, this
transformation would proceed by an electrophilic substitution on
position 2 of thiophene with intriguing electrophile species 4.
Formally, this transformation may be termed as an ‘aromatic ring
umpolung’. Whereas an electron-rich aromatic nucleus, such as
a phenol, normally reacts as a nucleophile and suitable oxidative
activation can convert it to a reactive electrophilic intermediate.
The high electronegativity of the oxygen atom in 3 was likely to
render this transient intermediate short-lived, excessively electro-
philic, and consequently very reactive, which may be intercepted
with external mild nucleophiles such as thiophene (Scheme 3).
In order to develop and improve this ‘novel’ transformation,
different carbon-based nucleophiles have been envisaged for the
O
O
R
OH
OH
R
Nu
Nu
a
[O]
[?]
+
b
1
4
5
6
R
Nu
R
Ph
I
O
O
OH
O
R
OAc
PhI(OAc)2
AcOH
AcO
1
2
3
4
R
R
R
OH
OH
E
Scheme 1.
9
1
R
R
E
However, we recently determined that carbon-based nucleo-
philes such as thiophene7 attack the presumed intermediate 4 at
OH
Nu
oxidative
activation
("umpolung")
O
Nu
10
("umpoled
reactivity")
R
4
R
* Corresponding author. Tel.: þ1 514 987 3000x5013; fax: þ1 514 987 4054.
E-mail address: canesi.sylvain@uqam.ca (S. Canesi).
Scheme 3.
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.05.114

7538
D. Be´rard et al. / Tetrahedron 64 (2008) 7537–7544
formation of new C–C bonds. These attempts have led to an un-
expected reaction that proceeds via a formal [2+3] cycloaddition.
This reaction can be usefully extended to polysubstituted aro-
matic phenols such as 16 or polycyclic ones such as 2-naphthol 18
(Scheme 6). In the case of 17, it seems to indicate that the process is
fairly insensitive to steric effects. In fact, 16 is quickly converted to
17 in good yield despite the presence of a bulky tert-butyl group at
the ortho position of the phenolic OH. Moreover, a unique cyclo-
adduct is observed with 2-naphthol.
2. Formal cycloaddition with furan
Interestingly, the use of furan in lieu of thiophene in the same
reaction produces none of the biaryl. Instead, it efficiently leads to
tricyclic compounds 12 resulting from a formal oxidative [2þ3]
cycloaddition (Scheme 4). The reaction, in this case, is best carried
out in TFE as the solvent (not HFIP; vide infra) and in the presence
of furan.8
t-Bu
t-Bu
O
PhI(OAc)2
O
OH
16
69%
17
O
O
(+/-)
OH
O
O
PhI(OAc)2
O
PhI(OAc)2
O
- H
O
H
R
OH
O
18
48%
19
4
11
12
(+/-)
O
R
R
Scheme 6.
Scheme 4.
The selectivity observed on compound 19 might be explained by
the fact that the electronegative oxygen in 18a would delocalize the
presumed cationic charge into ring A, with aromatic ring B in 18b
making this mesomer a stronger contributor to the overall delo-
calized system in comparison to 18c. No O-alkylation is observed;
we thought this point would be the key aspect of the trans-
formation (Scheme 7).
The difference between the behavior of thiophene and furan in
otherwise identical reactions may be rationalized considering that
the formation of the biaryl versus the tricyclic compound 12 de-
pends on the stability of the sulfonium 7 versus the oxonium 11
generated in the media. These results can be explained if we con-
sider that furan has a weaker aromatic character than thiophene.
Thus, the formed oxonium can be trapped by a nucleophilic attack
of the hydroxy and leads to 12, whereas the sulfonium is trans-
formed faster to the thiophene derivative via an elimination of the
first order leading to the biaryl 8. This latter species, electron richer
than the starting material is probably rapidly over oxidized into
inextractable tars of by-products; this may explain the low yield
of this transformation with thiophene. However, this intriguing
novel cyclization allows expeditious entry to the unusual dihy-
drofurobenzofuran9 skeleton 13, a ring system present in natural
products such as panacene 14, a shark antifeedant,10 psorofebrin 15,
an antileukemic xanthone,11 and other bioactive substances12
(Scheme 5).
A
B
B
A
B
A
O
O
O
18b
18a
Scheme 7.
18c
On the other hand, a very poor selectivity is observed with meta
alkyl substituted phenol. Indeed, oxidation of 3,4-xylenol 20 leads
to an inseparable w1:113 mixture of compounds 21 and 22 in 41%
yield (Scheme 8). Evidently, the methyl group at the meta position
exerts an insufficient degree of regiocontrol. In addition, oxidation
of 3-ethyl phenol 23 at ꢀ10 ꢁC leads to a mixture 2:3 of compounds
24 and 25 with a global yield of 46%. It should be stressed that, if the
reaction is conducted at ꢀ30 ꢁC, we observe a small augmentation
of the selectivity to 11:14.13 Experiments carried out at lower
temperature did not provide better results.
O
OH
H
H
H
OH
O
H
O
R
O
O
O
O
H
O
14
H
H
Br
15
13
OMe
OH
O
(~1:1)
+
O
PhI(OAc)2
O
Scheme 5.
O
O
Thus, to verify the scope of this novel reaction, various
20
41%
21
22
substituted phenols were converted to 12 in 38–61% yield. A sum-
mary of representative experiments with para-substituted phenols
appears in Table 1. It is worthy of note that the reaction tolerates
moderately nucleophilic functionalities, such as a sulfonamide,
which may be present on the substrate phenol (cf. entry e). A 4-
trimethylsilyl group is also readily tolerated (cf. entry f).
(+/-)
O
O
H
H
PhI(OAc)2
O
+
23
OH
O
24
O
25
46%
H
H
Scheme 8.
This reaction on 3-methoxy phenol 26 leads to corresponding
cycloadducts 28 and 29 with selectivity (w1:6) in favor of 29.13 It
should be noted that the methoxy group at position 3 exerts
a better degree of regiocontrol than the ethyl group of 23, probably
due to a stereoelectronic control. Indeed, electronic repulsion of the
lone pairs of oxygen would disfavor the approach of the furan by
pathway a in favor of pathway b (Scheme 9).
Table 1
O
O
(+/-)
PhI(OAc)2
TFE
R
OH
+
R
1
12
O
Entry
R
Yield
Compounds such as 12 are stable under neutral conditions and
can be chromatographed without incident. However, sub-
stoichiometric amounts of strong protonic acids, such as TFA, in-
duce rapid and quantitative isomerization to biaryls. This is
exemplified in Scheme 10 by the conversion of 12a to 31a. Phenols
31 are significantly more electron-rich than the starting species 4.
a
b
c
d
e
f
t-Bu
Me
OMe
CH2COOMe
CH2CH2NHTs
SiMe3
61
38
41
52
47
59

D. Be´rard et al. / Tetrahedron 64 (2008) 7537–7544
7539
O
developed in aprotic versus protic solvents may result in the dif-
ference in stability of the electrophilic species 4. Indeed, in aprotic
solvents, the excessively reactive intermediate should quickly po-
lymerize, if it is not stabilized by a lone pair of a donor group such as
a methoxy (via a quinonium species). In protic and poor nucleo-
philic solvents, such as TFE or HFIP (Kita’s conditions), this corre-
sponding electrophilic intermediate would be stabilized by the
solvent and would be sufficiently ‘stable’ to react with alkenes.
Thus, these protic conditions would allow this formal cycloaddition
to be extended to a large range of phenols. With a slightly electron-
rich alkene such as 4-acetoxystyrene 33, we observe a loss of yield.
Indeed, oxidation of compound 16 in the presence of 33, under
these conditions, leads to 37 in 23% yield and demonstrates that
this reaction is more efficient with electron richer-alkenes. The
presence of a hypothetical cation on 4 is intriguing.16 To bring a new
element, the same reaction has been carried out with 34. The oxi-
dation of the latter leads to 37 with an unprecedented ipso rear-
rangement, probably due to the stability of the tertiary carbocation
generated in situ; it would confirm the presence of a cationic
species (Scheme 12).
1:6
+
OMe
OH
O
PhI(OAc)2
Furan
O
MeO
36%
O
OMe
a
b
26
28
29
O
O
O
27
O
Scheme 9.
Consequently, they are more readily oxidized by DIB than the cor-
responding starting phenols, resulting in the formation of in-
tractable polymeric materials. Thus, it is essential to minimize
formation of 31 during the main oxidative process. In a sense, the
heterobicyclic system in 12 serves as a protecting group for the
phenolic functionality, and it prevents undesirable side reactions of
the latter and would explain why this reaction is rather inefficient
with thiophene.
H
O
Bu-t
OH
OH
O
(+/-)
+ H
OH
O
O
O
t-Bu
O
O
PhI(OAc)2
HFIP
- H
OAc
+
12a
30a
11a
31a
t-Bu
t-Bu
t-Bu
16
33
23%
t-Bu
OAc
Scheme 10.
21%
37
Available evidence suggests that compounds 12 are fairly stable
in media containing moderately acidic TFE. In contrast, the signif-
icantly more acidic HFIP appears to promote the conversion to 31 in
many cases, resulting in over oxidation and the ultimate formation
of much polymeric matter. We believe this to be the reason why
TFE, not HFIP, is the optimal reaction solvent in the present case.
Even so, we suspect that some loss of product through the above
sequence of events (formation of 31 and further oxidation) may
occur even during reactions run in TFE, because more than 1 equiv
of DIB is required to oxidize all the starting phenol.
Ar
O
OH
O
t-Bu
34
t-Bu
t-Bu
t-Bu
33
t-Bu
PhI(OAc)2
HFIP
t-Bu
36
35
Scheme 12.
In the case of 34, it seems to indicate that the oxidation process
is fairly insensitive to steric effects. On this basis, this reaction
would proceed through a cationic intermediate. To verify this hy-
pothesis, we have investigated the reactivity of numerous alkenes.
A reasonable choice to extend this reaction to enol ethers could be
the use of compounds such as dihydrofuran (DHF, n¼1) due to their
similarity to furan. Indeed, our first results led to the corresponding
tricyclic rings in moderate yield. This reaction occurs also with
dihydropyran (DHP, n¼2). The selectivity observed is consistent
with a cationic process to afford tetrahydrofurobenzofuran 39 or
dihydropyranobenzofuran cores 40 (Scheme 14). Moreover, this
novel extension of this reaction would be potentially useful in the
synthesis of natural products. Indeed, this system occurs in com-
pounds (n¼1) such as aflatoxin B2, 42, a food borne mutagenic
metabolite of Aspergillus flavus and versicolorin B2, 43, isolated
from Aspergillus parasiticus.17 The ‘direct oxidative [2þ3] cycload-
dition’ between a phenol and DHF, according to the format of
Scheme 13, seems to be a potentially short route to synthesize these
compounds. In the literature, different ways are known to get such
tricyclic acetal ring systems.18
3. Electrons-rich alkenes
We have also been interested in checking whether this reaction
could be extended to general alkenes sufficiently reactive to lead to
cycloadducts. In the literature and especially in the work of Swen-
ton’s group, a similar process is described in aprotic solvents be-
tween electrons-rich aromatics such as methoxy phenol derivatives
or isoeugenol and alkenes such as 4-methoxystyrene derivatives.14
In such case, it would proceed through a quinonium intermediate
due to the presence of a methoxy group at position 4. In the presence
of a quinonium species, this reaction is efficient in protic or aprotic
solvents with a similar yield (Scheme 11). Other similar processes
using quinonium or radical species deserve to be mentioned.15
This reaction can be extended to regular substituted phenols in
protic solvents to produce the corresponding dihydrobenzofuran
core. The difference in reactivity between formal cycloaddition
However, for the enol ether variant, the best solvent for this
reaction is HFIP. Indeed, reaction with TFE provides a mixture
(w1:1) of desired compound and a byproduct such as 5 resulting
from a nucleophilic attack of TFE in the para position (as shown in
Scheme 1, pathway b). This information lets us suppose that furan
reacts faster than enol ether. Indeed, no compound such as 5 is
observed in the same conditions with furan. Fortunately, the tri-
cyclic acetal ring is sufficiently stable to survive in acidic conditions
generated in the medium by HFIP. A summary of representative
experiments with para-substituted phenols appears in Table 2.
OMe
OMe
OMe
OH
H
PIFA, CH2Cl2
57%, ref 14b
O
O
O
O
O
or DIB,
HFIP, 54%
( )
32
H
OMe
4c
O
1c
Me
Me
Me
Scheme 11.

7540
D. Be´rard et al. / Tetrahedron 64 (2008) 7537–7544
Table 3
O
O
O
O
O
R
(n)
O
(n)
R'
(n)
R'
(+/-)
H
R
O
n= 1
or 2
O
OMe
O
(+/-)
n=1, 39
n=2, 40
4
38
PhI(OAc)2
HFIP
R
OH
47
OMe
R
48
R
49
O
O
OH
O
O
OH
H
R1
(n)
Entry
R
R0
Yield
O
O
O
a
b
c
d
e
t-Bu
Cl
Br
Ph
Me
H
H
H
H
44
32
33
23
37
O
O
O
43
H
HO
O
41
42
O
Scheme 13.
t-Bu
Table 2
chemistry. Similar examples of tetrahydrofurobenzofuran cores are
known.19
O
O
Although global yields of this transformation are moderate, this
ring making method is an impressive short access to the corre-
sponding tricyclic acetal core. This extension to cyclic enol ethers is
slightly less efficient than the one conducted with furan. It is
probably due to the fact that, even if phenols react faster with DIB
than enol ethers, they are not inert in the presence of DIB and are
oxidized into by-products. Moreover, a quite hindered base such as
lutidine is used to trap the acetic acid liberated in the medium
limiting possible cationic polymerization. Other attempts to gen-
eralize this reaction to unsubstituted aliphatic enol ethers such as
tert-butyl vinyl ether, vinyl acetate or ethyl vinyl ether were not
successful, probably due to the fact than polymerization of vinyl
occurred first.
O
(+/-)
PhI(OAc)2
HFIP
(n)
R
OH
+
(n)
R
4
n=1, 39
n=2, 40
Entry
R
Yield (n¼1)
Yield (n¼2)
a
b
c
d
e
t-Bu
Cl
Br
SiMe3
Ph
52
37
30
42
32
55
40
32
41
29
This reaction also succeeds with polysubstituted phenols such
as 16 and with polycyclic ones such as -naphthol 18 (Scheme 14).
b
4. Formal cycloaddition with allylsilanes
t-Bu
t-Bu
PhI(OAc)2
It should be noted that this oxidative annulation process occurs
only with quite electron-rich alkenes. Indeed, with alkenes that are
not electron-rich, such as styrene, indene, allyl bromine or allyl
acetate, no cycloaddition occurred and it led to the formation of
intractable polymeric materials. However, very important alkenes,
such as allylsilanes, are known to be good nucleophiles reacting on
electrophilic carbons efficiently.20 Allylsilanes should interact with
electrophilic intermediate 4 to afford 50. From this intermediate
two compounds should be obtained: a regular Sakurai (pathway a)
should lead to 51 or a cyclization (pathway b) could produce 52,
Scheme 16.
O
41, n=1, 52%
42, n=2, 55%
OH
16
O
O
(n)
(n)
(+/-)
PhI(OAc)2
O
43, n=1, 41%
44, n=2, 38%
O
OH
O
18
(n)
12
(n)
Scheme 14.
To verify the influence of the steric effect of a substituent at the
meta position, 3-ethyl phenol was oxidized. Although the cyclo-
addition occurs with furan, as previously, a different ratio (1:3) is
obtained. Indeed, 3-ethyl phenol 23 leads to 45 and 46 in 35% yield
(Scheme 15). The increasing selectivity is due to a new approach to
the double bond (attack 1–3) with more steric interactions com-
pared to the furan approach (attack 1–5) as described in Scheme 9.
SiR3
a
R
R
SiR3
O
50
b
O
4
a
b
R
O
R
O
SiR3
52
OH
O
(+/-)
+
O
Et
O
51
PhI(OAc)2
35%
OH
O
1:3
Scheme 16.
Et
Et
Scheme 15.
45
46
23
Surprisingly, only small amounts (5–10%) of compounds such as
50 and 51 were sometimes detected. The main product isolated is
the corresponding cycloadduct 52 resulting from the oxidative
annulation process. The formation of a cycloadduct (pathway b)
instead of the product 51 of a regular Sakurai reaction (pathway a)
would be explained by the stability of the electrophilic in-
termediate 50 due to the use of a protic solvent. Indeed, under this
condition, the cationic charge of 50 would be more stabilized by the
high ionizing power of the solvent and would be sufficiently stable.
This reaction can be extended to 3,4-dihydro-2-methoxy-2H-
pyran 48 to quickly yield the corresponding tricyclic compound 49
in an epimeric mixture of w1:1 (Table 3).
It should be stressed that this unusual bis-ketal structure 49 has
never been reported with a tetrahydrofurobenzopyran ring center
and should find useful applications in synthesis or in medicinal

D. Be´rard et al. / Tetrahedron 64 (2008) 7537–7544
7541
Thus, the formed carbocation 50 can be trapped by a nucleophilic
attack of the oxygen and leads to 52 instead of the elimination of
the TMS group. Once again, this method leads to heterocyclic
compounds such as dihydrofuran 53 in only one step. This structure
is equally present in many natural products such as arthrographol
54,21 a natural product isolated from Aspergillus oryzae or Arthog-
raphis pinicola, remirol 55,22 isolated from Remiria maritima, and
other bioactive substances (Scheme 17).23 While a number of useful
routes to substructure 54 are reported,24 we have become in-
terested in an ‘oxidative cycloaddition’ approach between phenols
and alkenes.25
Reaction with para cresol occurs in low yields (20%). These latter
results show some limits of our method and these unsatisfactory
results could be explained by formation of the corresponding qui-
none methide 56 that leads to inextractable tars of by-products,
Scheme 18. This problem could be overcome considering that the
reaction with bromine 52c or with iodine 52d would allow differ-
ent R chains with the palladium chemistry to be introduced.
Of course, this reaction also occurs with polycyclic phenols such
as b-naphthol 18 (44% of a single isomer) and with polysubstituted
ones such as 58 with a similar yield, Scheme 19.
Moreover, this reaction can be extended to dimethylpheny-
lallylsilane to lead to compound 61, a potential precursor of
arthrographol, via a potential Tamao–Fleming process27 (Scheme 20).
R1
OH
OH
O
O
OMe
OMe
OH
PhI(OAc)2
HFIP
45%
O
(+/-)
R
Si
Si
O
O
HO
Ph
MeO
Ph
61
MeO
53
54
Scheme 17.
55
60
MeO
Scheme 20.
This novel extension described between various substituted
If a compound such as 51 is almost not observed during the
oxidative reaction, the latter is produced by a treatment of 52a with
a Lewis acid such as boron trifluoride diethyl etherate (Scheme 21).
phenols and allyltrimethylsilane must be carried out in the pres-
ence of an excess of allyltrimethylsilane and also in solvents such as
TFE or HFIP with similar yield.26 As a matter of fact, corresponding
dihydrofuran cores 52 are quite stable in such acidic conditions. A
summary of representative experiments with para-substituted
phenols appears in Table 4. Regardless, the various examples pro-
vided herein suggest that the reaction is certainly synthetically
useful to obtain dihydrobenzofuran skeleton such as 52 quickly.
It should be stressed that the reaction is not efficient when
a benzylic hydrogen atom is in the para position (cf. entries f and g).
F
F
SiMe3
BF3,Et2O
CH2Cl2, 0 °C
O
OH
B
F
H2O
SiMe3
O
t-Bu
52a
t-Bu
62
51a
t-Bu
Scheme 21.
Table 4
5. Conclusion
O
(+/-)
PhI(OAc)2
HFIP
SiMe3
R
OH
+
In conclusion, formal [2þ3] cycloaddition is based on a common
electrophilic intermediate generated by an environmentally benign
hypervalent iodine reagent (DIB) in perfluorinated protic solvents.
This intermediate can react with different sufficiently reactive al-
kenes to lead in one step to different heterocyclic rings such as
dihydrofuranobenzofurans, tetrahydrofuranobenzofurans, tetrahy-
dropyranofurans, and dihydrobenzofurans. All these structures are
present in a number of natural products and could potentially lead
to a short route to these molecules. This transformation expands
novel strategic opportunities in the chemical synthesis of hetero-
oxygenated substances with an intriguing concept that could be
termed as an ‘aromatic ring umpolung’. New results in ongoing
investigations in this field will be disclosed in due course.
SiMe3
R
1
52
Entry
R
Yield
a
b
c
d
e
f
g
h
i
t-Bu
58
52
53
41
43
21
35
53
40
Cl
Br
I
OMe
CH2CH2OH
CH2CH2NHTs
SiMe3
OPh
6. Experimental protocols
H
R
O
O
Polymers
6.1. General
-H
R
4
56
Unless otherwise noted, NMR spectra were recorded in CDCl3 at
Scheme 18.
300 MHz for 1H and 75 MHz or 150 MHz for 13C. Chemical shift (
d)
are in parts per million and coupling constants (J) are in hertz.
Multiplicities are reported as: ‘s’ (singlet), ‘d’ (doublet), ‘dd’ (dou-
blet of doublets), ‘t’ (triplet), ‘q’ (quartet), ‘m’ (multiplet), ‘c’ (com-
plex), and ‘br’ broad. All reactions were monitored by TLC. Reagents
and solvents were commercial products and were used as received,
including trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP).
PhI(OAc)2
SiMe3
O
SiMe3
OH
18
44%
57
(+/-)
SiMe3
59
OMe
OMe
6.1.1. Cycloaddition with furan 12
PhI(OAc)2
SiMe3
Scheme 19.
O
At ꢀ10 ꢁC (ice/NaCl), a solution of PhI(OAc)2 (‘DIB’, 98 mg,
0.3 mmol, 1.5 equiv) in CF3CH2OH (‘TFE’, 0.35 mL) was added
dropwise for 1 min to a vigorously stirred solution of phenol 1
(0.2 mmol, 1 equiv) in furan (164 mg, 2.4 mmol, 12 equiv) and TFE
MeO
OH
58
MeO
46%

7542
D. Be´rard et al. / Tetrahedron 64 (2008) 7537–7544
(0.6 mL). The mixture was then stirred for 20 s, diluted with 6 mL of
ethyl acetate, poured into a separatory funnel, and washed with
3 mL of a satd solution of K2CO3 and 3 mL of brine. The solution was
concentrated under vacuum and the residue was purified by silica
gel chromatography with an appropriate mixture of ethyl acetate/
85:15) to afford compound 31a (21 mg, 0.095 mmol, 95%) as an oil.
1H (300 MHz, CDCl3)
¼7.54 (m, 2H), 7.25 (dd, 1H, J¼8.2, 2.3 Hz),
d
7.04 (br, 1H), 6.92 (d, 1H, J¼8.2 Hz), 6.72 (d, 1H, J¼3.5 Hz), 6.55 (dd,
1H, J¼3.5, 1.8 Hz), 1.34 (s, 9H). 13C (75 MHz, CDCl3)
¼150.1, 143.3,
d
141.1, 131.1, 126.5, 122.8, 116.7, 115.7, 111.6, 106.3, 34.1, 31.4. HMRS
(ESI): calcd for C14H17O2 (MHþ): 217.1223; found: 217.1225.
hexane. NMR data. Compound 12a: 1H (300 MHz, CDCl3)
d¼7.48 (d,
1H, J¼1.8 Hz), 7.34 (dd,1H, J¼8.2,1.8 Hz), 6.82 (d,1H, J¼8.2 Hz), 6.65
(d, 1H, J¼2.9 Hz), 6.06 (d, 1H, J¼7.6 Hz), 5.97 (dd, 1H, J¼7.6, 2.3 Hz),
6.1.2. Cycloaddition with 4-acetoxystyrene 37
5.31 (t, 1H, J¼2.3 Hz),1.33 (s, 9H). 13C (75 MHz, CDCl3)
d
¼157.1, 151.1,
At 0 ꢁC (ice/NaCl), a solution of PhI(OAc)2 (‘DIB’, 100 mg,
0.31 mmol, 1.55 equiv) in (CF3)2CHOH (‘HFIP’, 0.35 mL) was added
over 10 s to a vigorously stirred solution of phenol 16 or 34
(0.2 mmol, 1 equiv) in HFIP (0.6 mL) and 4-acetoxystyrene 33
(1.6 mmol, 8 equiv). The mixture was then stirred for 30 s, concen-
trated under vacuum and the residue was purified by silica gel
chromatography with a mixture of ethyl acetate/hexane (5:95). 1H
143.8, 128.4, 124.1, 122.9, 110.1, 100.0, 89.0, 85.5, 34.3, 31.6. HMRS
(ESI): calcd for C14H17O2 (MHþ): 217.1223; found: 217.1228. Com-
pound 12b: 1H (300 MHz, CDCl3)
d
¼7.24 (d, 1H, J¼1.8 Hz), 7.08 (dd,
1H, J¼8.2, 1.8 Hz), 6.77 (d, 1H, J¼8.2 Hz), 6.63 (d, 1H, J¼2.9 Hz), 6.03
(d, 1H, J¼7.6 Hz), 5.97 (dd, 1H, J¼7.6, 2.3 Hz), 5.31 (t, 1H, J¼2.3 Hz),
2.31 (s, 3H). 13C (75 MHz, CDCl3)
d¼157.2, 151.0, 131.8, 130.1, 126.5,
124.5, 110.4, 100.1, 88.8, 85.3, 20.6. HMRS (ESI): calcd for C11H11O2
(300 MHz, CDCl3)
d
¼7.41 (d, 2H, J¼8.2 Hz), 7.07 (d, 2H, J¼8.2 Hz),
(MHþ): 175.0754; found: 175.0749. Compound 12c: 1H (300 MHz,
6.91 (s, 1H), 6.86 (s, 1H), 5.73 (t, 1H, J¼8.2 Hz), 3.55 (dd, 1H, J¼15.4,
9.4 Hz), 3.08 (dd,1H, J¼15.4, 8.2 Hz), 2.31 (s, 3H), 2.29 (s, 3H), 1.39 (s,
CDCl3)
d
¼6.99 (d, 1H, J¼2.7 Hz), 6.86 (dd, 1H, J¼8.8, 2.7 Hz), 6.78 (d,
1H, J¼8.8 Hz), 6.63 (d, 1H, J¼2.7 Hz), 6.03 (d, 1H, J¼7.6 Hz), 5.97 (dd,
9H). 13C (150 MHz, CDCl3)
d¼169.4, 155.3, 150.0, 140.5, 132.3, 129.6,
1H, J¼7.6, 2.7 Hz), 5.29 (t, 1H, J¼2.7 Hz), 3.77 (s, 3H). 13C (75 MHz,
126.6,126.6,125.4,122.9,121.6, 82.8, 38.6, 34.0, 29.3, 21.1, 21.0 HMRS
(ESI): calcd for C17H17O4 (MHþ): 285.1121; found: 285.1125.
CDCl3)
d
¼154.1, 150.9, 150.9, 125.0, 117.8, 111.1, 110.7, 100.2, 89.0,
85.5, 56.0. HMRS (ESI): calcd for C11H11O3 (MHþ): 191.0703; found:
191.0704. Compound 12d: 1H (300 MHz, CDCl3)
d¼7.36 (d, 1H,
6.1.3. Cycloaddition with cyclic enol ethers 39/40/49
J¼1.8 Hz), 7.18 (dd, 1H, J¼8.2, 1.8 Hz), 6.82 (d, 1H, J¼8.2 Hz), 6.63 (d,
1H, J¼2.3 Hz), 6.04 (d, 1H, J¼7.6 Hz), 5.97 (dd, 1H, J¼7.6, 2.3 Hz),
5.30 (t, 1H, J¼2.3 Hz), 3.69 (s, 3H), 3.58 (s, 2H). 13C (75 MHz, CDCl3)
At ꢀ10 ꢁC (ice/NaCl), a solution of PhI(OAc)2 (‘DIB’, 100 mg,
0.31 mmol, 1.55 equiv) in (CF3)2CHOH (‘HFIP’, 0.35 mL) was added
over 10 s to a vigorously stirred solution of phenol 1 (0.2 mmol,
1 equiv) in HFIP (0.6 mL), lutidine (66.4 mg, 0.62 mmol, 3.1 equiv),
and enol ether (3 mmol, 15 equiv). The mixture was then stirred for
30 s, concentrated under vacuum, and the residue was purified by
silica gel chromatography with a mixture of ethyl acetate/hexane
(5:95). NMR data of dihydrofurans. Compound 39a: 1H (300 MHz,
d
¼172.2,151.2,132.2,130.3,127.1,126.2,125.0,110.8, 99.9, 89.2, 85.0,
52.0, 40.3. HMRS (ESI): calcd for C13H13O4 (MHþ): 233.0808; found:
233.0808. Compound 12e: 1H (300 MHz, CDCl3)
d
¼7.69 (d, 2H,
J¼8.2 Hz), 7.28 (d, 2H, J¼8.2 Hz), 6.97 (dd, 1H, J¼8.2, 1.7 Hz), 6.74 (d,
1H, J¼8.2 Hz), 6.61 (d, 1H, J¼2.7 Hz), 5.97 (m, 2H), 5.29 (t, 1H,
J¼2.7 Hz), 4.56 (t, 1H, J¼7.1 Hz), 3.17 (q, 2H, J¼7.2 Hz), 2.70 (t, 2H,
CDCl3)
d
¼7.21 (d, 1H, J¼1.7 Hz), 7.17 (dd, 1H, J¼8.2, 1.7 Hz), 6.73 (d,
J¼7.2 Hz), 2.42 (s, 3H). 13C (75 MHz, CDCl3)
d¼154.1, 150.9, 150.9,
1H, J¼8.2 Hz), 6.30 (d, 1H, J¼6.0 Hz), 4.06 (t, 1H, J¼7.7 Hz), 3.99 (dd,
1H, J¼8.2, 6.0 Hz), 3.65 (ddd, 1H, J¼12.1, 8.2, 4.9 Hz), 2.30 (m, 1H),
2.08 (dd, 1H, J¼11.5, 4.4 Hz), 1.30 (s, 9H). 13C (75 MHz, CDCl3)
125.0, 117.8, 111.1, 110.7, 100.2, 89.0, 85.5, 56.0. HMRS (ESI): calcd for
C
19H20O4N1S1 (MHþ): 358.1108; found: 358.1112. Compound 12f:
1H (300 MHz, CDCl3)
d¼7.59 (d, 1H, J¼1.6 Hz), 7.42 (dd, 1H, J¼8.2,
d
¼157.1, 144.1, 127.1, 125.4, 121.4, 111.0, 108.3, 67.1, 46.7, 34.3, 33.5,
1.6 Hz), 6.87 (d, 1H, J¼8.2 Hz), 6.61 (d, 1H, J¼2.7 Hz), 6.04 (d, 1H,
J¼7.7 Hz), 5.94 (dm,1H, J¼7.7 Hz), 5.28 (t,1H, J¼2.7 Hz), 0.23 (s, 9H).
31.6. HMRS (ESI): calcd for C14H19O2 (MHþ): 219.1380; found:
219.1374. Compound 39b: 1H (300 MHz, CDCl3)
d¼7.14 (d, 1H,
13C (75 MHz, CDCl3)
d¼160.1, 151.2, 136.5, 131.8, 131.4, 124.4, 110.5,
J¼1.7 Hz), 7.09 (dd, 1H, J¼8.2, 1.7 Hz), 6.72 (d, 1H, J¼8.2 Hz), 6.31 (d,
1H, J¼6.0 Hz), 4.08 (t,1H, J¼7.7 Hz), 3.98 (dd,1H, J¼8.2, 6.0 Hz), 3.63
(ddd, 1H, J¼12.1, 8.2, 4.9 Hz), 2.30 (m, 1H), 2.04 (dd, 1H, J¼11.5,
99.9, 88.9, 85.1, ꢀ0.8. HMRS (ESI): calcd for C13H17O2Si (MHþ):
233.0992; found: 233.0997. Compound 17: 1H (300 MHz, CDCl3)
d
¼7.12 (s, 1H), 7.04 (s, 1H), 6.60 (d, 1H, J¼2.3 Hz), 6.03 (d, 1H,
J¼8.2 Hz), 5.96 (dm, 1H, J¼8.2 Hz), 5.30 (t, 1H, J¼2.3 Hz), 2.32 (s,
3H), 1.35 (s, 9H). 13C (75 MHz, CDCl3)
¼150.5, 133.8, 129.7, 128.5,
125.0, 123.9, 100.5, 87.8, 85.3, 34.0, 29.1, 20.8. HMRS (ESI): calcd for
15H19O2 (MHþ): 231.1380; found: 231.1378. Compound 19: 1H
(300 MHz, CDCl3)
4.4 Hz). 13C (75 MHz, CDCl3)
d¼158.0, 129.5, 128.5, 125.7, 124.7,
111.4, 110.1, 67.2, 46.5, 33.3. HMRS (ESI): calcd for C10H10O2Cl
d
(MHþ): 197.0364; found: 197.0371. Compound 39c: 1H (300 MHz,
CDCl3)
d
¼7.29 (d, 1H, J¼1.7 Hz), 7.24 (dd, 1H, J¼8.2, 1.7 Hz), 6.68 (d,
C
1H, J¼8.2 Hz), 6.31 (d, 1H, J¼6.0 Hz), 4.08 (t, 1H, J¼7.7 Hz), 3.98 (dd,
1H, J¼8.2, 6.0 Hz), 3.61 (ddd, 1H, J¼12.1, 8.2, 4.9 Hz), 2.30 (m, 1H),
d
¼7.92 (d, 1H, J¼8.2 Hz), 7.84 (d, 1H, J¼8.2 Hz),
7.82 (d, 1H, J¼8.2 Hz), 7.56 (td, 1H, J¼8.2, 1.2 Hz), 7.37 (td, 1H, J¼8.2,
1.2 Hz), 7.15 (d, 1H, J¼9.4 Hz), 6.69 (d, 1H, J¼2.9 Hz), 6.52 (d, 1H,
J¼7.6 Hz), 6.17 (dm, 1H, J¼7.0 Hz), 5.38 (t, 1H, J¼2.9 Hz). 13C
2.05 (dd, 1H, J¼11.5, 4.4 Hz). 13C (75 MHz, CDCl3)
¼158.5, 131.5,
d
130.1, 127.7, 112.8, 111.4, 110.7, 67.2, 46.4, 33.4. HMRS (ESI): calcd for
C
11H10O2Br (MHþ): 240.9859; found: 240.5851. Compound 39d: 1H
(300 MHz, CDCl3)
(75 MHz, CDCl3)
d
¼157.5, 151.2, 137.4, 132.4, 130.9, 130.1, 128.6,
d
¼7.31 (dþs, 2H, J¼8.2 Hz), 6.82 (d, 1H, J¼8.2 Hz),
127.5, 123.3, 122.1, 112.8, 99.9, 89.8, 85.1. HMRS (ESI): calcd for
14H11O2 (MHþ): 211.0754; found: 211.0746. Compound 29: 1H
(300 MHz, CDCl3)
¼7.33 (d, 1H, J¼8.2 Hz), 6.63 (d, 1H, J¼2.2 Hz),
6.31 (d, 1H, J¼5.5 Hz), 4.08 (t, 1H, J¼8.2 Hz), 4.0 (t, 1H, J¼7.1 Hz),
3.63 (m, 1H), 2.32 (m, 1H), 2.09 (dd, 1H, J¼12.0, 4.9 Hz), 0.25 (s, 9H).
C
d
13C (75 MHz, CDCl3)
d
¼160.1, 134.8, 134.0, 132.1, 129.6, 110.9, 108.8,
6.50 (dd, 1H, J¼8.2, 2.2 Hz), 6.42 (d, 1H, J¼2.2 Hz), 6.02 (m, 2H), 5.29
67.2, 46.3, 33.5, ꢀ0.8. HMRS (ESI): calcd for C13H19O2Si (MHþ):
(t, 1H, J¼2.2 Hz), 3.78 (s, 3H). 13C (75 MHz, CDCl3)
¼162.7, 161.0,
d
235.1149; found: 235.1152. Compound 39e: 1H (300 MHz, CDCl3)
151.3, 126.6, 116.9, 107.4, 99.8, 96.2, 90.0, 85.0, 55.4. HMRS (ESI):
d
¼7.53 (d, 2H, J¼8.2 Hz), 7.46–7.36 (m, 4H), 7.29 (t, 1H, J¼7.5 Hz),
calcd for C11H11O3 (MHþ): 191.0703; found: 191.0704.
6.87 (d, 1H, J¼8.2 Hz), 6.37 (d, 1H, J¼5.6 Hz), 4.15–4.03 (m, 2H), 3.68
Biaryl 31a. To a stirred solution of 12a (22 mg, 0.1 mmol) in
dichloromethane (1 mL) under argon at 0 ꢁC was added TFA (24 mg,
0.02 mmol). The solution was stirred at room temperature for
20 min (verified by TLC) and quenched with satd aq NaHCO3 (2 mL).
The aqueous phase was extracted with ethyl acetate (2ꢂ5 mL), the
combined organic layers were washed with brine (4 mL), dried over
Na2SO4, and concentrated under reduced pressure. The crude
product was quickly filtered by chromatography (n-hexane/EtOAc,
(m, 1H), 2.35 (m, 1H), 2.13 (dd, 1H, J¼12.0, 4.9 Hz). 13C (75 MHz,
CDCl3)
d¼159.0, 141.0, 134.7, 128.7, 128.3, 127.7, 126.7, 126.6, 123.5,
111.3, 109.3, 67.2, 46.5, 33.5. HMRS (ESI): calcd for C16H15O2 (MHþ):
239.1067; found: 239.1070. Compound 41: 1H (300 MHz, CDCl3)
d
¼6.89 (s, 1H), 6.86 (s, 1H), 6.30 (d, 1H, J¼6.0 Hz), 4.04 (t, 1H,
J¼8.2 Hz), 3.92 (t, 1H, J¼7.0 Hz), 3.57 (m, 1H), 2.29 (mþs, 4H), 2.02
(dd, 1H, J¼12.3, 4.7 Hz), 1.36 (s, 9H). 13C (75 MHz, CDCl3)
¼157.1,
d
144.1, 127.1, 125.4, 121.4, 111.0, 108.3, 67.1, 46.7, 34.3, 33.5, 31.7.

D. Be´rard et al. / Tetrahedron 64 (2008) 7537–7544
7543
HMRS (ESI): calcd for C15H21O2 (MHþ): 233.1536; found: 233.1531.
Compound 43: 1H (300 MHz, CDCl3)
J¼8.2 Hz), 4.90 (m, 1H), 3.26 (dd, 1H, J¼15.4, 8.2 Hz), 2.82 (dd, 1H,
J¼15.4, 8.2 Hz), 1.26 (mþs, 4H), 1.05 (dd, 1H, J¼14.3, 8.8 Hz), 0.09 (s,
d¼7.83 (d, 1H, J¼8.2 Hz), 7.71
(d, 2H, J¼8.8 Hz), 7.52 (t, 1H, J¼7.6 Hz), 7.34 (t, 1H, J¼7.6 Hz), 7.12 (d,
1H, J¼8.8 Hz), 6.51 (d, 1H, J¼5.5 Hz), 4.34 (t, 1H, J¼7.1 Hz), 4.12 (t,
1H, J¼8.2 Hz), 3.64 (m, 1H), 2.41 (m, 1H), 2.30 (m, 1H). 13C (75 MHz,
9H). 13C (75 MHz, CDCl3)
d
¼158.0, 129.4, 127.6, 124.8, 118.4, 110.0,
82.9, 38.1, 25.1, ꢀ0.8. HMRS (ESI): calcd for C12H18OClSi (MHþ):
241.0810; found: 241.0811. Compound 52c: 1H (300 MHz, CDCl3)
CDCl3)
d
¼156.7, 130.1, 129.7, 129.6, 129.0, 126.9, 123.0, 122.0, 118.3,
d
¼7.23 (d, 1H, J¼1.7 Hz), 7.18 (dd, 1H, J¼8.2, 1.7 Hz), 6.60 (d, 1H,
111.8, 111.6, 67.4, 45.9, 31.8. HMRS (ESI): calcd for C14H13O2 (MHþ):
J¼8.2 Hz), 4.93 (m, 1H), 3.27 (dd, 1H, J¼15.4, 8.2 Hz), 2.79 (dd, 1H,
J¼15.4, 8.2 Hz), 1.30 (dd, 1H, J¼14.3, 6.6 Hz), 1.09 (dd, 1H, J¼14.3,
213.0910; found: 213.0912. NMR data of dihydropyrans. Compound
40a: 1H (300 MHz, CDCl3)
d
¼7.17 (dþs, 2H, J¼8.2 Hz), 6.79 (d, 1H,
8.8 Hz), 0.09 (s, 9H). 13C (75 MHz, CDCl3)
d
¼158.0, 129.4, 127.6,
J¼8.2 Hz), 5.87 (d, 1H, J¼6.6 Hz), 3.85–3.65 (m, 2H), 3.29 (dd, 1H,
124.8, 118.4, 110.0, 82.9, 38.1, 25.1, ꢀ0.8. HMRS (ESI): calcd for
12H18OBrSi (MHþ): 285.0305; found: 285.0313. Compound 52d:
1H (300 MHz, CDCl3)
J¼11.5, 5.5 Hz), 2.05 (m, 1H), 1.92 (m, 1H), 1.60 (m, 2H), 1.31 (s, 9H).
C
13C (75 MHz, CDCl3)
d
¼156.0, 144.0, 128.9, 124.9, 120.6, 108.8, 104.2,
d¼7.41 (d, 1H, J¼1.7 Hz), 7.36 (dd, 1H, J¼8.2,
61.1, 38.9, 34.3, 31.7, 22.8, 20.1. HMRS (ESI): calcd for C15H21O2
1.7 Hz), 6.51 (d, 1H, J¼8.2 Hz), 4.92 (m, 1H), 3.26 (dd, 1H, J¼15.4,
8.2 Hz), 2.77 (dd, 1H, J¼15.4, 8.2 Hz), 1.29 (dd, 1H, J¼14.3, 6.6 Hz),
1.07 (dd, 1H, J¼14.3, 8.8 Hz), 0.08 (s, 9H). 13C (75 MHz, CDCl3)
(MHþ): 233.1536; found: 233.1542. Compound 40b: 1H (300 MHz,
CDCl3)
1H, J¼6.6 Hz), 3.81–3.62 (m, 2H), 3.27 (dd, 1H, J¼11.5, 5.5 Hz), 2.01
(m, 1H), 1.83 (m, 1H), 1.54 (m, 2H). 13C (75 MHz, CDCl3)
d¼7.08 (dþs, 2H, J¼8.2 Hz), 6.74 (d, 1H, J¼8.2 Hz), 5.86 (d,
d
¼159.3, 136.6, 133.5, 130.4, 111.5, 82.8, 37.8, 25.1, ꢀ0.9. HMRS (ESI):
d¼156.9,
calcd for C12H18OISi (MHþ): 333.0166; found: 333.0162. Compound
129.4, 128.1, 125.7, 124.0, 110.7, 104.5, 61.0, 38.8, 22.5, 19.8. HMRS
52e: 1H (300 MHz, CDCl3)
d¼6.71 (s, 1H), 6.62 (d, 1H, J¼8.2 Hz), 6.58
(ESI): calcd for C11H12O2Cl (MHþ): 211.0520; found: 211.0511.
(d, 1H, J¼8.2 Hz), 4.85 (m, 1H), 3.71 (s, 3H), 3.21 (dd, 1H, J¼15.4,
8.2 Hz), 2.74 (dd, 1H, J¼15.4, 8.2 Hz), 1.28 (dd, 1H, J¼14.3, 6.6 Hz),
1.07 (dd, 1H, J¼14.3, 8.8 Hz), 0.07 (s, 9H). 13C (75 MHz, CDCl3)
Compound 40c: 1H (300 MHz, CDCl3)
d
¼7.26 (dþs, 2H, J¼8.2 Hz),
6.74 (d, 1H, J¼8.2 Hz), 5.89 (d, 1H, J¼6.6 Hz), 3.83–3.65 (m, 2H), 3.31
(dd, 1H, J¼11.5, 5.5 Hz), 2.04 (m, 1H), 1.87 (m, 1H), 1.60 (m, 2H). 13
C
d
¼153.7, 128.3, 113.1, 112.5, 111.3, 108.9, 82.3, 56.0, 38.6, 25.1, ꢀ0.8.
(75 MHz, CDCl3)
d
¼157.4, 131.9, 131.0, 126.9, 112.8, 111.3, 104.5, 61.0,
HMRS (ESI): calcd for C13H21O2Si (MHþ): 237.1305; found: 237.1296.
38.7, 22.5, 19.8. HMRS (ESI): calcd for C11H10O2Br (MHþ): 255.0015;
Compound 52f: 1H (300 MHz, CDCl3)
d¼7.01 (d, 1H, J¼1.7 Hz), 6.94
found: 255.0011. Compound 40d: 1H (300 MHz, CDCl3)
d
¼7.28 (d,
(dd, 1H, J¼8.2, 1.7 Hz), 6.67 (d, 1H, J¼8.2 Hz), 4.91 (m, 1H), 3.81 (t,
2H, J¼6.4 Hz), 3.26 (dd, 1H, J¼15.4, 8.2 Hz), 2.79 (m, 3H), 1.33 (dd,
1H, J¼14.3, 6.6 Hz), 1.09 (dd, 1H, J¼14.3, 8.8 Hz), 0.10 (s, 9H). 13C
1H, J¼8.2 Hz), 6.79 (d, 1H, J¼8.8 Hz), 5.89 (d, 1H, J¼6.6 Hz), 3.83–
3.64 (m, 2H), 3.31 (dd, 1H, J¼11.5, 5.5 Hz), 2.05 (m, 1H), 1.86 (m, 1H),
1.60 (m, 2H), 1.31 (s, 9H). 13C (75 MHz, CDCl3)
d¼159.1, 133.6, 131.9,
(75 MHz, CDCl3)
d¼158.1, 129.7, 128.3, 127.8, 125.4, 109.0, 82.3, 63.9,
129.2, 128.5, 109.3, 104.2, 61.0, 38.5, 22.7, 20.0, ꢀ0.7. HMRS (ESI):
38.5, 38.2, 25.2, ꢀ0.8. HMRS (ESI): calcd for C14H23O2Si (MHþ):
calcd for C14H21O2Si (MHþ): 249.1305; found: 249.1310. Compound
251.1462; found: 251.1463. Compound 52g: 1H (300 MHz, CDCl3)
40e: 1H (300 MHz, CDCl3)
d
¼7.55 (d, 2H, J¼8.2 Hz), 7.48–7.37 (m,
d
¼7.68 (d, 2H, J¼8.2 Hz), 7.29 (d, 2H, J¼8.2 Hz), 6.85 (d, 1H,
4H), 7.32 (t, 1H, J¼7.2 Hz), 6.94 (d, 1H, J¼8.2 Hz), 5.96 (d, 1H,
J¼6.6 Hz), 3.89–3.69 (m, 2H), 3.39 (dd, 1H, J¼11.5, 6.0 Hz), 2.10 (m,
J¼1.7 Hz), 6.76 (dd,1H, J¼8.2,1.7 Hz), 6.60 (d,1H, J¼8.2 Hz), 4.89 (m,
1H), 4.40 (t, 1H, J¼6.6 Hz), 3.21 (dd, 1H, J¼15.4, 8.2 Hz), 3.15 (q, 2H,
J¼6.6 Hz), 2.74 (dd, 1H, J¼15.4, 8.2 Hz), 2.66 (t, 2H, J¼6.6 Hz), 2.42
(s, 3H), 1.31 (dd, 1H, J¼14.3, 6.6 Hz), 1.09 (dd, 1H, J¼14.3, 8.8 Hz),
1H), 1.97 (m, 1H), 1.62 (m, 2H). 13C (75 MHz, CDCl3)
d
¼157.9, 141.1,
134.6, 130.0, 128.6, 127.2, 126.7, 126.5, 122.6, 109.8, 104.5, 61.0, 38.7,
22.6, 19.9. HMRS (ESI): calcd for C17H17O2 (MHþ): 253.1223; found:
0.09 (s, 9H). 13C (75 MHz, CDCl3)
d¼158.3, 143.3, 136.8, 129.6, 128.8,
253.1226. Compound 42: 1H (300 MHz, CDCl3)
d
¼6.91 (s, 1H), 6.82
128.0, 127.9, 127.0, 125.1, 109.1, 82.4, 44.5, 38.1, 35.0, 25.2, 21.5, ꢀ0.9.
(s, 1H), 5.89 (d, 1H, J¼6.0 Hz), 3.71 (m, 2H), 3.26 (q, 1H, J¼5.5 Hz),
3.57 (m, 1H), 2.31 (s, 3H), 2.04 (m, 1H), 1.87 (dd, 1H, J¼13.7, 5.0 Hz),
HMRS (ESI): calcd for C21H30NO3SSi (MHþ): 404.1710; found:
404.1720. Compound 52h: 1H (300 MHz, CDCl3)
d
¼7.31 (d, 1H,
1.62 (m, 1H), 1.52 (m, 1H), 1.38 (s, 9H). 13C (75 MHz, CDCl3)
d
¼154.3,
J¼1.7 Hz), 7.27 (dd, 1H, J¼8.2, 1.7 Hz), 6.76 (d,1H, J¼8.2 Hz), 4.92 (m,
1H), 3.29 (dd, 1H, J¼15.4, 8.2 Hz), 2.81 (dd, 1H, J¼15.4, 8.2 Hz), 1.34
(dd, 1H, J¼14.3, 6.6 Hz), 1.11 (dd, 1H, J¼14.3, 8.8 Hz), 0.24 (s, 9H),
132.5, 129.8, 129.5, 125.5, 121.9, 103.5, 60.5, 38.5, 33.9, 29.2, 22.4,
21.1, 19.8. HMRS (ESI): calcd for C16H23O2 (MHþ): 247.1693; found:
247.1693. Compound 44: 1H (300 MHz, CDCl3)
d
¼7.82 (d, 1H, J¼
0.11 (s, 9H). 13C (75 MHz, CDCl3)
d¼160.2, 133.3, 130.5, 129.7, 127.0,
8.2 Hz), 7.71 (d, 1H, J¼8.8 Hz), 7.66 (d, 1H, J¼8.2 Hz), 7.47 (t, 1H,
J¼8.2 Hz), 7.31 (t, 1H, J¼8.2 Hz), 7.16 (d, 1H, J¼8.8 Hz), 6.12 (d, 1H,
J¼6.6 Hz), 3.94 (m, 2H), 3.63 (q, 1H, 7.1 Hz), 2.29 (m, 1H), 1.75 (m,
108.9, 82.2, 38.0, 25.3, ꢀ0.7. HMRS (ESI): calcd for C15H27OSi2
(MHþ): 279.1595; found: 279.1599. Compound 52i: 1H (300 MHz,
CDCl3)
d
¼7.29 (t, 2H, J¼8.2 Hz), 7.02 (t, 1H, J¼8.2 Hz), 6.94 (d, 2H,
2H), 1.57 (m, 1H). 13C (75 MHz, CDCl3)
d
¼154.7, 130.3, 129.4, 129.1,
J¼8.2 Hz), 6.85 (d, 1H, J¼1.7 Hz), 6.79 (dd, 1H, J¼8.2, 1.7 Hz), 6.68 (d,
1H, J¼8.2 Hz), 4.93 (m, 1H), 3.26 (dd, 1H, J¼15.4, 8.2 Hz), 2.79 (dd,
1H, J¼15.4, 8.2 Hz), 1.34 (dd, 1H, J¼14.3, 6.6 Hz), 1.13 (dd, 1H, J¼14.3,
129.0, 126.6, 122.9, 122.4, 122.1, 112.1, 105.6, 61.2, 37.3, 24.0, 20.5.
HMRS (ESI): calcd for C15H15O2 (MHþ): 227.1067; found: 227.1071.
8.8 Hz), 0.10 (s, 9H). 13C (75 MHz, CDCl3)
d¼158.8, 155.7, 149.6,
6.1.4. Cycloaddition with allylsilanes 52
129.4, 128.7, 122.0, 119.3, 117.3, 117.0, 109.3, 82.7, 38.4, 25.2, ꢀ0.8.
HMRS (ESI): calcd for
18H23O2Si (MHþ): 299.1462; found:
299.1455. Compound 57: 1H (300 MHz, CDCl3)
¼7.76 (d, 1H,
A solution of PhI(OAc)2 (‘DIB’, 98 mg, 0.3 mmol, 1.5 equiv) in
(CF3)2CHOH (‘HFIP’, 0.35 ml) was added dropwise over 30 s to
a vigorously stirred solution of phenol 1 (0.2 mmol, 1 equiv) in
allyltrimethylsilane (230 mg, 2 mmol, 10 equiv) and HFIP (0.6 ml).
The mixture was then stirred for 30 s, concentrated under vacuum,
and the residue was purified by silica gel chromatography with
a mixture of ethyl acetate/hexane (5:95). Compound 52a: 1H
C
d
J¼8.2 Hz), 7.63 (d, 1H, J¼8.2 Hz), 7.54 (d, 1H, J¼8.2 Hz), 7.43 (t, 1H,
J¼8.2 Hz), 7.27 (d, 1H, J¼8.2 Hz), 7.05 (d, 1H, J¼8.2 Hz), (m, 1H), 5.10
(m, 1H), 3.56 (dd, 1H, J¼14.8, 8.8 Hz), 3.03 (dd, 1H, J¼14.8, 8.2 Hz),
1.37 (dd,1H, J¼13.7, 6.6 Hz),1.18 (dd,1H, J¼14.3, 8.8 Hz), 0.11 (s, 9H).
13C (75 MHz, CDCl3)
d
¼156.8, 130.8, 128.9, 128.7, 128.6, 126.4, 122.5,
(300 MHz, CDCl3)
d
¼7.31 (d, 1H, J¼1.7 Hz), 7.27 (dd, 1H, J¼8.2,
122.5, 118.5, 112.1, 82.9, 36.9, 25.6, ꢀ0.7. HMRS (ESI): calcd for
16H21OSi (MHþ): 257.1356; found: 257.1350. Compound 59: 1H
(300 MHz, CDCl3)
¼6.35 (s, 2H), 4.92 (m, 1H), 3.84 (s, 3H), 3.77 (s,
1.7 Hz), 6.76 (d, 1H, J¼8.2 Hz), 4.92 (m, 1H), 3.29 (dd, 1H, J¼15.4,
8.2 Hz), 2.81 (dd, 1H, J¼15.4, 8.2 Hz), 1.34 (dd, 1H, J¼14.3, 6.6 Hz),
1.11 (dd, 1H, J¼14.3, 8.8 Hz), 0.24 (s, 9H), 0.11 (s, 9H). 13C (75 MHz,
C
d
3H), 3.22 (dd, 1H, J¼15.4, 8.2 Hz), 2.79 (dd, 1H, J¼15.4, 8.2 Hz), 1.42
CDCl3)
d
¼156.8, 130.8, 128.7, 128.6, 126.4, 122.5, 122.5, 118.5, 112.1,
(dd, 1H, J¼14.3, 6.6 Hz), 1.19 (dd, 1H, J¼14.3, 8.8 Hz), 0.10 (s, 9H). 13
C
82.9, 36.9, 25.6, ꢀ0.7. HMRS (ESI): calcd for C16H27OSi (MHþ):
(75 MHz, CDCl3)
d
¼154.4, 144.3, 141.9, 128.3, 101.4, 99.1, 82.9, 56.0,
263.1826; found: 263.1817. Compound 52b: 1H (300 MHz, CDCl3)
38.9, 30.9, 25.0, ꢀ0.9. HMRS (ESI): calcd for C14H23O3Si (MHþ):
d¼7.32 (d, 1H, J¼1.7 Hz), 7.08 (dd, 1H, J¼8.2, 1.7 Hz), 6.66 (d, 1H,
267.1411; found: 267.1414. Compound 61: 1H (300 MHz, CDCl3)

7544
D. Be´rard et al. / Tetrahedron 64 (2008) 7537–7544
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¼7.53 (m, 2H), 7.36 (m, 3H), 6.33 (s, 1H), 6.29 (s, 1H), 4.89 (m, 1H),
866–870; (d) Chan, C.; Li, C.; Zhang, F.; Danishefsky, S. J. Tetrahedron Lett. 2006,
47, 4839–4841.
3.83 (s, 3H), 3.73 (s, 3H), 3.06 (dd, 1H, J¼15.4, 8.2 Hz), 2.69 (dd, 1H,
J¼15.4, 8.2 Hz), 1.69 (dd, 1H, J¼4.3, 6.6 Hz), 1.39 (dd, 1H, J¼14.3,
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haran, H. J. Chem. Soc., Perkin Trans. 1 1995, 2855–2860; (d) Brimble, M. A.;
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8.8 Hz), 0.38 (s, 3H), 0.37 (s, 3H). 13C (75 MHz, CDCl3)
d¼154.4,
144.3, 141.8, 138.2, 133.5, 129.1, 128.2, 127.8, 101.3, 99.1, 82.6, 55.9,
38.7, 24.3, ꢀ2.2, ꢀ2.4. HMRS (ESI): calcd for C19H25O3Si (MHþ):
329.1567; found: 329.1573.
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Acknowledgements
Acknowledgement is made to the Donors of the American
Chemical Society Petroleum Research Fund (ACS PRF) for support of
this research. We are also very grateful to the Natural Sciences and
Engineering Research Council of Canada (NSERC) and to the pro-
vincial government of Quebec (FQRNT).
´
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