Synthesis of complex ortho-allyliodoarenes by employing the reductive iodonio-claisen rearrangement

Article abstract of DOI:10.1002/chem.201202049

The reductive iodonio-Claisen rearrangement (RICR), involving complex aromatic λ³-iodanes and allyltrimethylsilane, was investigated. The RICR reaction of complex substituted aromatic hypervalent iodine (III) compounds and an allylmetal partner was conducted. The anionic oxy Cope rearrangement was found to be approximately 10¹⁰ to 10¹⁷ times faster than the neutral oxy Cope rearrangement due to weakening of the adjacent C-C bond by the oxygen anion. The results also indicate that the steric and electronic nature of the aromatic λ³-iodanes is the dominant factor influencing the [3,3]-sigmatropic rearrangement reaction. The removal of tert-butyl ether protecting group by using trifluroacetic acid in dichloromethane in the presence of triisopropylsilane gives the natural product broussin in 39% yield.

Full text of DOI:10.1002/chem.201202049

COMMUNICATION
DOI: 10.1002/chem.201202049
Synthesis of Complex ortho-Allyliodoarenes by Employing the Reductive
Iodonio-Claisen Rearrangement
Hem Raj Khatri and Jianglong Zhu*[a]
Hypervalent iodine compounds have been widely used as
oxidants for a number of oxidation reactions due to their
unique chemical reactivity and environmentally benign char-
acter.[1] Over the past two decades, tremendous research
effort in this field has led to the preparation and application
allenylACTHNGUTERNN(UG aryl)iodinanes that subsequently underwent the
RICR reaction to yield various ortho-propargyliodoarenes.
This particular rearrangement was also observed later by
Norton and co-workers.[6] Additional evidence of the occur-
rence of RICR reactions involving the reaction of l3-iodanes
and allyltrimethylsilane[7] or resorcinol derivatives[8,9] have
also been reported. All of these previous efforts involved
relatively simple l3-iodanes, and limited studies[5] were car-
ried out to understand the influence of the sterics and elec-
tronics of the aromatic hypervalent iodine compounds on
the RICR reaction. In short, this type of pericyclic reaction
is relatively unexplored.
of various synthetically useful iodineACTHNUTRGNEUNG
(III)[2] and iodine(V)[3,4]
reagents. In these hypervalent iodine-mediated reactions, re-
duced iodoarene derivatives were usually generated as by-
products. Despite the fact that iodoarene byproducts are not
considered environmentally harmful, these reactions were
not atom economic, mainly because of the loss of aromatic
iodide functionality in the chemical waste. Therefore, the
development of hypervalent iodine chemistry with signifi-
cantly improved atom efficiency would be very appealing.
Herein, we wish to report our investigation into the reduc-
tive iodonio-Claisen rearrangement (RICR), involving com-
Based on this previously reported evidence, we planned
to study the RICR reaction of complex substituted aromatic
hypervalent iodineACTHNUTRGNEUNG(III) compounds and an allylmetal part-
ner (Scheme 1). Substituted aromatic l3-iodanes 1[10] should
plex
aromatic
l3-iodanes
and
allyltrimethylsilane
react with allylmetal species in the presence of a suitable
(Scheme 1). Through this pericyclic reaction, the versatile
Lewis acid to initially form allylphenyliodoniumACTHNGUETRNNU(G III) com-
plex 2.[7] Intermediate 2, being used as an allylating agent,[7]
may undergo the reductive iodonio-Claisen rearrangement
under optimized conditions to give advanced dearomatized
species 3. Rearomatization of 3 should allow access to vari-
ous substituted ortho-allyliodoarenes 4,[11,12] which are very
useful building blocks[13,14] in organic synthesis due to the
versatility of both the alkene and aryliodide functional
groups in further transformations.
Scheme 1. A strategy for the synthesis of ortho-allyliodoarenes by reduc-
tive iodonio-Claisen rearrangement.
With this idea in mind, we initiated our studies by using
iodosylbenzene 7 and allyltrimethylsilane in the presence of
a Lewis acid promoter (Table 1). When BF3·Et2O was em-
ployed, ortho-allyliodobenzene 4a was obtained in a ratio of
0.24:1 to iodobenzene 6a (Table 1, entry 2), albeit a 36%
yield was isolated by Oh and co-workers (Table 1, entry 1).[7]
No desired product was detected in the absence of a Lewis
acid or by using other Lewis acids, such as SnCl4, TiCl4, and
ZnCl2 (Table 1, entries 3–6). In addition, varying the sol-
vents and temperature, as well as using magnesium sulfate
as an additive,[5] did not improve the yield of ortho-allylio-
dobenzene 4a. Furthermore, iodobenzene diacetate (1a)
and phenyliodine bis(trifluoroacetate) (8) were also tested
in this RICR reaction, and similar results were obtained
(Table 1, entries 7 and 8). Despite the fact that analogous re-
actions between iodobenzene diacetate 1a and propargylsi-
lanes were feasible,[5] these results suggested that reactions
involving allylsilanes are problematic.
aromatic iodide functionality is transferred from hypervalent
iodine reagents to the products—ortho-allyliodoarenes.
The discovery of the reductive iodonio-Claisen rearrange-
ment was first reported by Ochiai and co-workers in the
early 1990s.[5] In their experiments, relatively simple l3-io-
danes were mixed with propargylsilanes, -germanes, or -stan-
nanes in the presence of boron trifluoride diethyl etherate
(BF3·Et2O), which led to the formation of hypervalent
[a] H. R. Khatri, Prof. Dr. J. Zhu
Department of Chemistry and
School for Green Chemistry and Engineering
The University of Toledo
2801 W. Bancroft Street, Toledo, OH 43606 (USA)
Fax : (+1)419-530-4033
E-mail: Jianglong.Zhu@Utoledo.edu
We reasoned that the side product, iodobenzene (6a),
may be produced through reductive elimination of an allyl-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201202049.
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Table 1. Screening of various l3-iodanes and Lewis acids in RICR reac-
Therefore, we shifted our efforts to investigate the effect of
aromatic substituents on this RICR reaction, with the hope
that variation of the steric and electronic nature of the l3-io-
danes may favor [3,3]-sigmatropic rearrangement over re-
ductive elimination.
tions.[a]
Accordingly, iodoarene diacetates 1b–i, containing either
an electron-donating or an electron-withdrawing group,
were screened in the RICR reaction by using standard ex-
perimental conditions (allyltrimethylsilane, BF3·Et2O,
CH2Cl2, À258C, 2 h; Table 1, entries 9–16). These experi-
ments led to the identification of a very promising substrate,
3-methoxyiodobenzene diacetate 1 f, which reacted with al-
lyltrimethylsilane to provide a mixture of 4-allyl-3-iodoani-
sole 4 f, 2-allyl-3-iodoanisole 5 f, and 3-iodoanisole 6 f (4 f/
5 f/6 f=3.8:0.9:1; Table 1, entry 13), whereas reactions in-
volving the other IIII-containing compounds (1b–e and 1g–i)
produced the corresponding iodoarene 6 as the major prod-
uct. It is worth noting that neither 2-methoxyiodobenzene
diacetate 1e nor 4-methoxyiodobenzene diacetate 1g pro-
duced a significant amount of the corresponding ortho-ally-
liodoarene products (Table 1, entries 12 and 14). 3-Methylio-
dobenzene diacetate 1c gave an improved result over the
parent iodobenzene diacetate 1a (Table 1, entry 10), where-
as 2-methyl- and 4-methyliodobenzene diacetates (1b and
1d) produced comparable results to the parent iodobenzene
diacetate 1a (Table 1, entries 9 and 11). In addition, l3-io-
danes 1h and 1i, containing 3-trifluoromethyl- and 3-bromo-
substituents provided only a trace amount of the desired
products, although this was not completely unexpected
(Table 1, entries 15 and 16). These studies indicated that an
electron-donating group at the meta-position is required to
favor the [3,3]-sigmatropic rearrangement reaction. In addi-
tion, 3-methoxyiodosylbenzene (9), prepared by alkaline hy-
drolysis[21] of 1 f, gave a comparable experimental outcome
to 1 f (Table 1, entry 17). However, the use of 3-methoxy-
Entry
l3-Iodanes
Lewis acid
Ratio
(4/5/6)[b]
Yield
[%][c]
AHCTUNGTRENNUNG
1[7]
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
7
7
7
7
7
7
1a
8
1b
1c
1d
1e
1 f
1g
1h
1i
9
BF3·Et2O
BF3·Et2O
none
SnCl4
TiCl4
not reported
(36)
n.d.
0
0
0
0.24:0:1[d]
–
–
–
–
ZnCl2
0
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
BF3·Et2O
0.1:0:1[d]
0.2:0:1[e]
0.17:0:1[e]
0.32:0.22:1
0.08:0:1[g]
–
n.d.
n.d.
n.d.
80[f]
n.d.
trace
68 (55)
trace
trace
trace
65 (52)
n.d.
3.8:0.9:1
–
–
–
4.5:1.1:1
1.4:0.4:1
10
[a] Reaction conditions: [bisACHTNUTRGNEUNG(acetoxy)iodo]arene (0.6 mmol), allyltrime-
1
thylsilane (0.9 mmol), Lewis acid (0.72 mmol). [b] Estimated by H NMR
analysis of the crude products. [c] Combined isolated yield of regioisom-
ers 4 and 5. The isolated yield of major isomer 4 is reported in parenthe-
ses. n.d.=not determined. [d] Ratio of ortho-allyliodobenzene 4a to iodo-
benzene 6a. [e] Ratio of 2-allyl-6-methyliodobenzene 4b to 2-methylio-
dobenzene 6b. [f] Combined isolated yield of 4c, 5c and 6c. [g] Ratio of
2-allyl-4-methyliodobenzene 4d to 4-methyliodobenzene 6d.
AHCTUNGTRENNUNG
(bis(trifluoroacetoxy)iodo)benzene (10)[22] provided an infe-
rior result (Table 1, entry 18), probably because the strongly
electron-withdrawing nature of trifluoroacetate promotes
the reductive elimination reaction. Therefore, iodoarene di-
acetates will be prepared and studied in the RICR reactions
because they are more readily available and more stable
than their iodosylarene counterparts.
ACHTUNGTRENNUNG(phenyl)iodoniumACHTUNGTRENNUNG(III) complex (see 2), a reaction that com-
petes with the reductive iodonio-Claisen rearrangement. If
so, acceleration of the [3,3]-sigmatropic rearrangement or
suppression of reductive elimination should favor formation
of ortho-allyliodobenzene 4a. It is well-known that a related
pericyclic reaction, the Claisen rearrangement, can be accel-
erated by electron-withdrawing or electron-donating sub-
stituents.[15] In addition, the anionic oxy–Cope rearrange-
ment was found to be approximately 1010 to 1017 times faster
than the neutral oxy–Cope rearrangement,[16] probably be-
Because 3-methoxyiodobenzene diacetate 1 f was identi-
fied as a promising substrate for this RICR reaction, further
optimization of the reaction conditions was carried out by
using this substrate (Table 2). Our investigations resulted in
the discovery that acetonitrile is a superior solvent for this
rearrangement, which significantly increased the proportion
of the ortho-allyliodoarenes (4 f and 5 f) formed relative to
iodoarene 6 f (Table 2, entry 2). Presumably, acetonitrile sta-
bilizes the iodoniumACTHNUTRGNE(NUG III) species (see 2, Scheme 1) through
cause of weakening of the adjacent C C bond by the
coordination[23] to the iodine center and thus suppresses the
reductive elimination reaction. Lowering the temperature
also slightly improved the reaction outcome (Table 2,
entry 5). Further optimization led to the discovery that
using a mixed solvent (CH2Cl2/CH3CN (1:1), À508C) pro-
vided the optimal reaction conditions, under which the de-
À
oxygen anion, as suggested by the density functional theory
(DFT) calculations.[17] Furthermore, the introduction of a
thioalkoxy group on the C4 or C6 position[18,19] or additional
unsaturated substituents on the terminal position has been
found to accelerate anionic oxy–Cope rearrangements.[20]
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Reductive Iodonio-Claisen Rearrangement
COMMUNICATION
Table 2. Optimization of the reaction conditions of the RICR reaction
Table 3. RICR reactions involving complex substituted l3-iodanes.[a]
involving 1 f.[a]
Entry
Reaction conditions
4 f/5 f/6 f[b]
Yield
[%][c]
1
2
3
4
5
6
7
MeOH, À258C
–
trace
CH3CN, À258C
9.1:2.2:1
–
0.9:0.15:1
5.6:0.9:1
8.3:1.9:1
10:1.6:1
n.d.[d]
trace
THF, À258C
Et2O, À258C
n.d.[d]
n.d.[d]
n.d.[d]
86 (74)
CH2Cl2, À808C
CH2Cl2/CH3CN (1:9), À258C
CH2Cl2/CH3CN (1:1), À508C
[a] Reaction conditions: [bisACHTNUTRGNEUNG(acetoxy)iodo]arene (0.6 mmol), allyltrime-
thylsilane (0.9 mmol), BF3·Et2O (0.72 mmol). [b] Estimated by 1H NMR
analysis of the crude products. [c] Combined isolated yield of regioisom-
ers 4 f and 5 f. Isolated yield of major isomer 4 f is reported in parenthe-
ses. n.d.=not determined. [d] Based on the analysis of the crude reaction
mixtures, these conditions provided similar or inferior yields to entry 7,
but with less of the desired product 4 f. Consequently, these crude mix-
tures were not further purified.
Entry
l3-Iodanes
4/5/6[b]
Yield
[%][c]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1j
1k
1l
1m
1n
1o
1p
1q
1r
1s
1t
1u
1v
1w
8.3:2.6:1
3.2:1.2:1
1.1:0.2:1
4.0:1.2:1
1.33:0:0:1
10:0:1
16.7:0.17:1
33:6.6:1
2.9:0:1
3.0:0.06:1
2.5:0:1
5.6:0.97 :1
7.14:0:1
2.34:2.08:1
93 (66)
59 (42)
90[d]
76[e]
85[f]
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
sired 2-allyl-5-methoxyiodobenzene was isolated in 74%
yield (Table 2, entry 7). When l3-iodanes 1a–e and 1g–i
were investigated under these optimal conditions, the corre-
sponding iodoarenes (6a–e and 6g–i, respectively) were still
produced as the major component in the product mixtures.
These results indicate that the steric and electronic nature
of the aromatic l3-iodanes is the dominant factor influencing
the [3,3]-sigmatropic rearrangement reaction.
85 (68)
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
75 (64)
73 (41)
N
[a] Reaction conditions: [bisACHTNUTRGNEUNG(acetoxy)iodo]arene (0.6 mmol), allyltrime-
1
thylsilane (0.9 mmol), Lewis acid (0.72 mmol). [b] Estimated by H NMR
analysis of the crude products. [c] Combined isolated yield of regioisom-
ers 4 and 5. The isolated yield of major isomer 4 is reported in parenthe-
ses. [d] Combined yield of an inseparable mixture of 4l, 5l and 6l.
[e] Combined yield of an inseparable mixture of 4m, 5m and 6m.
[f] Combined yield of an inseparable mixture of 4n and 6n.
Next, we studied the scope of this reductive iodonio-Clais-
en rearrangement reaction with respect to complex iodoar-
ene diacetates containing electron-donating groups at the
C3 position. Thus, complex di-, tri-, and tetrasubstituted aro-
matic l3-iodanes 1j–t containing alkoxy, acetamido, and car-
bamate functionalities at C3 were prepared from their io-
doarene precursors 6j–t by following standard proce-
dures.[24,25] Under the optimized conditions, these l3-iodanes
reacted with allyltrimethylsilane to give their corresponding
ortho-allylarenes in synthetically useful to good yields
(Table 3, entries 1–11). 2-Allyl-5-tert-butoxyiodobenzene 4k
was produced in only a moderate yield, probably because of
the instability of the tert-butoxy group in the presence of
BF3·Et2O (Table 3, entry 2). Iodoarene diacetates 1r and 1s,
containing an arylbromide, worked well in this RICR reac-
tion, providing ortho-allyliodoarenes in which an aromatic
bromide functionality may enable further transformations
(Table 3, entries 10 and 11). In addition, indoline-derived io-
doarene diacetate 1u and tetrahydroquinoline-derived io-
doarene diacetates 1v and 1w were also prepared[25] and in-
vestigated in this type of pericyclic reaction. The structures
of tetrahydroquinoline-derived iodoarene diacetates 1v and
1w were unambiguously confirmed by analysis of the single-
crystal X-ray diffraction pattern.[25] These bicyclic aromatic
ortho-allyliodoarenes 4u–w in moderate to good yields
(Table 3, entries 12–14).
To gain insight into the mechanism of this reductive iodo-
nio-Claisen rearrangement reaction, we performed a reac-
tion between 3-methoxyliodobenzene diacetate 1 f and a
deuterated (E)-allyldimethylphenylsilane 11[26] under the op-
timal condition, which provided a mixture of products 12,
13, and 6 f (12/13/6 f=9.5:1.6:1, Scheme 2). The desired
ortho-allyliodoarene 12, in which deuterium was completely
incorporated at the terminal position of the alkene, was iso-
lated in 76% yield. In addition, the stereochemistry of the
alkene in both products 12 and 13 was found to be com-
pletely scrambled (E/Z=1:1).[27] We also carried out a reac-
tion between 4-methoxyiodobenzene diacetate 1g and deu-
terated allylsilane 11 under similar conditions, which pro-
duced mainly 4-iodoanisole 6g and deuterated allyl acetate
14, together with a trace amount of ortho-allyliodoarene 4g
(Scheme 2).[28] It should be noted that deuterium was incor-
porated at only the allylic position of allyl acetate 14.
bis
ACHTUNGTRENNUNG(acetoxy)iodoarenes also underwent reductive iodonio-
Claisen rearrangement reactions to provide complex bicyclic
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J. Zhu and H. R. Khatri
bipyramidal complex 17 in
which the aryl and acetate li-
gands occupy the axial position.
Reductive elimination of com-
plex 17 may lead to the forma-
tion of iodoarene 6 and allyl
acetate 14 as byproducts. As in-
dicated by the experimental re-
sults, the [3,3]-sigmatropic rear-
rangement is accelerated if Y is
an electron-donating group,
which leads to the isolation of
ortho-allyliodoarenes as the
major products.
Scheme 2. Reductive iodonio-Claisen rearrangements involving deuterated allyldimethylphenylsilane 11.
To demonstrate the potential
utility of complex ortho-allylio-
doarenes, we have carried out a
concise synthesis of broussin,
an antifungal natural product
isolated from wounded xylem
tissues of paper mulberry
shoots by Takahashi and co-
workers.[30] As depicted in
Scheme 4, ortho-allyliodoarene
4k underwent hydroboration–
oxidation to give alcohol 18 in
63% yield, which was subse-
quently oxidized (PCC/CH2Cl2)
to the corresponding aldehyde
19 (81%). Addition of 4-me-
Scheme 3. Proposed mechanism.
The experimental results involving deuterated allyldime-
thylphenylsilane support the proposed mechanism involving
the iodonio-Claisen rearrangement as shown in Scheme 3.[29]
Accordingly, the reaction of deuterated allylsilane with l3-
iodane in the presence of BF3·Et2O should provide pseudo-
thoxyphenylmagnesium bromide to aldehyde 19 at À788C
provided alcohol 20 (90%), which gave dihydrobenzopyran
À
21 (87%) upon palladium-catalyzed intramolecular C O
bond formation.[31] Final removal of tert-butyl ether protect-
ing group in 21 by using trifluroacetic acid in dichlorome-
thane in the presence of triisopropylsilane gave the natural
product (Æ)-broussin in 39% yield.
trigonal-bipyramidal allylaryliodoniumACTHNUTRGNEUNG
(III) complex 15[7] in
which both the allyl and acetate ligands occupy the axial po-
sitions.[23] Complex 15 will undergo [3,3]-sigmatropic rear-
rangement and subsequent rearomatization to provide
In conclusion, we have developed a reductive iodonio-
Claisen rearrangement involving complex aromatic hyperva-
ortho-allyliodoarene
12
(III) complex 15 may equilibrate with its
isomer 16,
as
the
major
product.
lent iodineACTHNGUETRNNU(G III) compounds and allyltrimethylsilane to pro-
duce synthetically valuable ortho-allyliodoarenes. It was
Allylaryliodonium
conformational
N
which will lead to the formation
of the minor product, ortho-al-
lyliodoarene 13 due to the dis-
favored steric and electronic ef-
fects. In this [3,3]-sigmatropic
rearrangement, the deuterium
will be incorporated at the ter-
minal carbon atom of the
alkene and it is expected that
the olefin stereochemistry will
be scrambled, as observed in
the experiments. On the other
Scheme 4. Reagents and conditions: i) BH3·SMe2, then H2O2, NaOH. ii) pyridinium chlorochromate (PCC),
hand,
complexes 15 or 16 may isomer-
ize to another pseudotrigonal- 08C.
allylaryliodoniumACTHNGUTER(NNUG III)
CH2Cl2; iii) 4-methoxyphenylmagnesium bromide, À788C; iv) Pd
A
phino-1,1’-binaphthyl (24 mol%), Cs2CO3, toluene, 808C; v) CF3CO2H (5%) in CH2Cl2, triisopropylsilane,
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Reductive Iodonio-Claisen Rearrangement
COMMUNICATION
[11] In ref. [7], Oh and co-workers detected the formation of ortho-ally-
liodobenzene as a byproduct; however, no discussion was reported
regarding its formation.
[12] A related Claisen-type rearrangement involving hypervalent sulfur
was reported to provide ortho-allylarylsulfides. See: A. J. Eberhart,
J. E. Imbriglio, D. J. Procter, Org. Lett. 2011, 13, 5882–5885.
[13] a) A. Padwa, H. Lipka, S. H. Watterson, S. S. Murphree, J. Org.
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[14] C.-Y. Liu, P. Knochel, Org. Lett. 2005, 7, 2543–2546.
[15] A. M. Martꢂn Castro, Chem. Rev. 2004, 104, 2939–3002.
[16] D. A. Evans, A. M. Golob, J. Am. Chem. Soc. 1975, 97, 4765–4766.
[17] H. Baumann, P. Chen, Helv. Chim. Acta 2001, 84, 124–130.
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[21] H. Saltzman, J. G. Sharefkin, Org. Synth. 1963, 43, 60–61.
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found that an electron-donating group at the meta-position
is required to favor the [3,3]-sigmatropic rearrangement
over reductive elimination. Experimental results involving
deuterated allylsilane support the reaction mechanism in-
volving a [3,3]-sigmatropic rearrangement. This method has
also been successfully applied to the concise synthesis of an
antifungal natural product, broussin. The development and
application of related reductive iodonio-Claisen rearrange-
ments in organic synthesis is currently underway and will be
reported in due course.
Acknowledgements
The startup funding from The University of Toledo is gratefully acknowl-
edged. We thank Dr. Kristin Kirschbaum and Mr. Nicholas Amato for
single-crystal X-ray diffraction analysis, Professors Mark Mason and
Steve Sucheck for helpful suggestions, and Mr. James Dunaway and Mr.
Christopher Lopez for experimental assistance.
[23] M. Ochiai in Topics in Current Chemistry, Vol. 224, Hypervalent
Iodine Chemistry: Modern Developments in Organic Synthesis (Ed.:
T. Wirth), Springer, Berlin, 2003, pp. 5–68.
Keywords: allylation
compounds · iodine · pericyclic reaction · rearrangement
·
aryl iodide
·
hypervalent
[24] A. McKillop, D. Kemp, Tetrahedron 1989, 45, 3299–3306.
[25] See the Supporting Information for experimental details.
[26] D. Orain, J.-C. Guillemin, J. Org. Chem. 1999, 64, 3563–3566.
1
[27] The E/Z ratio of 1:1 was determined by H NMR analysis.
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Received: June 8, 2012
Revised: July 10, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
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These are not the final page numbers!

J. Zhu and H. R. Khatri
I(o)dide behind the wheel: Aromatic
hypervalent iodineACTHNUGRTNEUNG(III) compounds
Hypervalent Iodine
reacted with allyltrimethylsilane in the
presence of a Lewis acid to give ortho-
allyliodoarenes through a reductive
iodonio-Claisen rearrangement (see
scheme). An meta-electron-donating
group in the l3-iodanes was indispensa-
ble to favor the [3,3]-sigmatropic rear-
rangement over reductive elimination.
The method was successfully used for
the concise synthesis of an antifungal
natural product, broussin.
H. R. Khatri, J. Zhu* ........ &&&& — &&&&
Synthesis of Complex ortho-Allylio-
doarenes by Employing the Reductive
Iodonio-Claisen Rearrangement
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www.chemeurj.org
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!