Iodine(III)-mediated cyclization of unsaturated O-alkyl hydroxamates: Silyl-assisted access to α-vinyl and α-(2-silylvinyl) lactams

Article abstract of DOI:10.1055/s-0031-1290750

The embodiment of lactam rings within a wealth of physiologically active natural products and pharmaceutical agents ensures that the development of synthetic methods, which facilitate the preparation of these saturated N-heterocycles, is of critical importance. Herein the development of a versatile method for the synthesis of 4 to 8-membered -vinyl and -(2-silylvinyl) lactams involving the iodine(III)-mediated oxidative cyclization of unsaturated O-alkyl hydroxamates, which encompass an allylsilane, is reported. Importantly, the outcome of this transformation can be effectively controlled through variation of the substitution pattern at the silicon center. While allyltrimethylsilanes undergo ring closure with desilylation to form -vinyl lactams, the corresponding triisopropyl and triphenylsilanes cyclize without loss of the larger silyl group to form E-vinylsilanes with excellent stereoselectivity. From a mechanistic standpoint, it is proposed that this reaction proceeds via concerted alkene addition of a singlet nitrenium ion (or its equivalent) to form a bicyclic N-acyl-N-alkoxyaziridinium ion, which undergoes eliminative ring opening. Georg Thieme Verlag Stuttgart New York.

Full text of DOI:10.1055/s-0031-1290750

SPECIAL TOPIC
▌1199
special topic
Iodine(III)-Mediated Cyclization of Unsaturated O-Alkyl Hydroxamates:
Silyl-Assisted Access to α-Vinyl and α-(2-Silylvinyl) Lactams
α-Vinyl Lactams via Nitrenium-Allylsilane Addition
Duncan J. Wardrop,* Maria V. Yermolina, Edward G. Bowen
University of Illinois at Chicago, Department of Chemistry, 845 West Taylor Street, Chicago, IL 60607-7061, USA
Fax +1(312)9660431; E-Mail: wardropd@uic.edu
Received: 20.02.2012; Accepted: 24.02.2012
In this regard, we recently reported a versatile alkene ox-
amidation method for the preparation of α-hydroxyalkyl
lactams 3, which is believed to take place via the concert-
ed intramolecular alkene addition of acylnitrenium ions 4
Abstract: The embodiment of lactam rings within a wealth of phys-
iologically active natural products and pharmaceutical agents en-
sures that the development of synthetic methods, which facilitate
the preparation of these saturated N-heterocycles, is of critical im-
portance. Herein the development of a versatile method for the syn- to form bicyclic aziridinium ions 5 (Scheme 1).11 In most
thesis of 4 to 8-membered α-vinyl and α-(2-silylvinyl) lactams
involving the iodine(III)-mediated oxidative cyclization of unsatu-
cases, concerted ion pair collapse of these highly reactive
species occurs solely at the less encumbered α-position to
rated O-alkyl hydroxamates, which encompass an allylsilane, is re-
yield α-trifluoroacetoxyalkyl lactams 6. The nitrenium
ported. Importantly, the outcome of this transformation can be
ion intermediates in this case appear to be singlet in nature
effectively controlled through variation of the substitution pattern at
and are generated under mild conditions, through the che-
moselective N-oxidation of unsaturated O-alkyl hydrox-
amates 1 with phenyliodine(III) bis(trifluoroacetate)
(PIFA).12 In the current article, we report on the develop-
ment of a versatile synthetic method for the preparation of
4–8-membered α-vinyl and α-(2-silylvinyl) lactams,
which involves the oxidative cyclization of O-alkyl hy-
droxamates that encompass an allylsilane moiety rather
than a simple alkene.
the silicon center. While allyltrimethylsilanes undergo ring closure
with desilylation to form α-vinyl lactams, the corresponding triiso-
propyl and triphenylsilanes cyclize without loss of the larger silyl
group to form E-vinylsilanes with excellent stereoselectivity. From
a mechanistic standpoint, it is proposed that this reaction proceeds
via concerted alkene addition of a singlet nitrenium ion (or its
equivalent) to form a bicyclic N-acyl-N-alkoxyaziridinium ion,
which undergoes eliminative ring opening.
Key words: nitrenium ion, allylsilane, hypervalent iodine, O-alkyl
hydroxamate, aziridinium
R
H
Allylsilanes are versatile nucleophiles, which undergo re-
giocontrolled addition and substitution with a broad range
electrophiles.1 While the role of electron-deficient carbon,
oxygen, and sulfur species in this context has been exten-
sively investigated, there are comparatively few examples
of the reaction of nitrogen-based electrophiles with allyl-
silanes. Of the various transformations reported to date,
including nitrene-mediated aziridination,2 addition to ar-
yldiazonium ions3 and azo compounds,4 the cycloaddition
of azides,5 and nitration with nitronium ion salts,6,7 the re-
action of allylsilanes with nitrenium ions (R2N+) is the
least well studied. Indeed, only two examples of this pro-
cess have previously been reported. Takeuchi has exam-
ined the reaction of arylnitrenium ions with cyclic allylic
1. PIFA
R
+
O
O
N
N
2. NH3
MeOH
O
NH
MeO
R
OH
MeO
MeO
3a (R = Me)
3b (R = H)
1a (R = Me)
1b (R = H)
2
R
H
2
3
TFA
PhI(OTFA)2
R
NH3
MeOH
Ph-I
+
TFA
0% 91%
E1/2
R
Me 18% 58%
α
β
H
SN2
O
–OCOCF3
OMe
[2+1]
+
N
N
O
p
R
OTFA
N
σ
+
MeO
MeO
4 (1A1)
O
8
silanes in the presence of AlCl3 while Abramovitch has
6
5
employed allyltrimethylsilane as a nucleophilic trap for
the photolytically generated 1,2,4-triazolyl cation.9 The
paucity of studies in this area, in common with the limited
synthetic deployment of nitrenium ions in general, has
historically arisen because of a lack of methods for the
generation of these highly electron-deficient species un-
der mild conditions.10
Scheme 1 Iodine(III)-mediated oxidative cyclization of unsaturat-
ed O-alkyl hydroxamates
Our interest in the reaction of nitrenium ions with allylsi-
lanes arose during the development of the aforementioned
oxamidation methodology and specifically with the ob-
servation that, in contrast to disubstituted olefin 1b, tri-
substituted alkene 1a, underwent cyclization to form α-
vinyl lactam 2 in addition to the expected oxamidation
product 3a (Scheme 1).11a From a mechanistic standpoint,
the formation of compound 2 was rationalized in terms of
the eliminative ring opening of the sterically encumbered
SYNTHESIS 42170012, 44,81199–1207
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1
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DOI: 10.1055/s-0031-1290750; Art ID: SS-2012-C0180-ST
© Georg Thieme Verlag Stuttgart · New York

1200
D. J. Wardrop et al.
SPECIAL TOPIC
aziridinium ion 5 (R = Me).13 That extended exposure of As summarized in Table 1, allylsilane preparation via
trifluoroacetate 6, the first-formed product of substitutive cross-metathesis was readily accomplished through the
ring opening, to trifluoroacetic acid did not change the use of the Grubbs second-generation catalyst (Grubbs II,
product ratio 2:3a added credence to our assumption that 15),19 using a three-fold excess of the appropriate allylsi-
2 arises directly from 5 rather than through the elimination lane 13 in CH2Cl2 (0.5 M) at reflux. In all cases, but 14a
of ester 6.
(Table 1, entry 1) and 14d (entry 3), cross-metathesis pro-
ceeded with reasonable to high selectivity for the E-iso-
mer. In cases where the Z-isomer was not detected by 1H
or 13C NMR spectroscopy, a selectivity of greater than
25:1 is suggested. In other cases, chromatographic isomer
separation was not possible and silane mixtures were nec-
essarily carried forward. While the low diastereoselectiv-
ity observed during the formation of 14d was unexpected,
Gouverneur has previously noted that the O-benzyl ana-
logue of β,γ-unsaturated ester 12a undergoes cross-
metathesis with only moderate selectivity (dr = 3:1).17f
In order to tap this unanticipated reaction manifold, we
decided to explore the cyclization of allylsilane-based
substrates 7 as a means to purposely promote eliminative
ring opening and thus formation of α-vinyl lactams 11
(Scheme 2). In this case, it was anticipated that upon con-
certed alkene addition of nitrenium ion 8,14 the presence
of a silylmethyl substituent in the resulting aziridinium
ion 9 would not only promote elimination to β-silyl carbo-
cation 10 through intercession of the β-effect,1 but also
disfavor substitutive ring opening at the neighboring α-
position by virtue of its steric encumbrance. A priori, it
was uncertain whether N-oxidation of the hydroxamate
group in 7 could be achieved selectively since allylsilanes
are known to undergo electrophilic substitution with io-
dine(III)-based reagents.15,16
Table 1 Preparation of Allylsilanes 14 via Cross-Metathesisa
Si(R1)3
O
O
13 (3 equiv)
MeO
MeO
n
n
15 (2.5 mol%)
CH2Cl2, reflux
R2
Si(R1)3
R2
12 (R2 = H)
14 (R2 = H)
R2
R2
PIFA
n
n
E/Z ratioc
Entry
12
n
R
14
Yield
(%)b
Si(R1)3
+
O
NH
MeO
O
N:
Si(R1)3
MeO
7
8
1
a
b
dd
e
f
0
1
2
3
4
1
2
3
1
2
3
Me
Me
Me
Me
Me
i-Pr
i-Pr
i-Pr
Ph
a
b
d
e
f
92
90
87
85
80
75
68
57
83
74
37
2:1
R2
2
>25:1
>25:1
8:1
α
Si(R1)3
R2
R2
n
n
n
β
3
+
O
O
N
N
N
+
OMe
MeO
MeO
4
O
Si(R1)3
9
10
11
5
10:1
2:1
Scheme 2 Nitrenium-alkene addition: silyl-assisted access to α-vi-
nyl lactams
6
g
h
i
g
h
i
7
6:1
Our investigation commenced with the development of a
general route to unsaturated O-alkyl hydroxamates 7. As
outlined in Scheme 3, our approach to these substrates
centered on the installation of the allylsilane moiety
through cross-metathesis between ω-unsaturated esters 12
(R2 = H) and simple, commercially available allylsilanes
13. The cross-metathesis of these nucleophilic alkenes is
often efficient and has been successfully employed for the
direct assembly of more complex allylsilanes in a number
of cases.17,18
8
6:1
9
j
j
>25:1
>25:1
>25:1
10
11
k
l
Ph
k
l
Ph
a Conditions: 12, 13 (3 equiv), Grubbs-II (15; 2.5 mol%), CH2Cl2 (0.5
M), reflux.
b Isolated yields, after purification by flash chromatography.
c Isomer ratio determined by 1H NMR spectroscopy.
d For the preparation of hydroxamate 7c, see Table 2 and Scheme 4.
O
cross-metathesis
O
(catalyst 15)
MeO
MeO
Introduction of the hydroxamate ester functionality neces-
sary for the generation of the nitrenium ion intermediate
was now accomplished by saponification of 14 and amide
coupling. The latter step was accomplished by conversion
of the carboxylic acids to the corresponding mixed anhy-
drides, using isobutyl chloroformate, and in situ coupling
with methoxylamine hydrochloride in the presence of tri-
ethylamine (Table 2).
Si(R1)3
n
n
R2
Si(R1)3
R2
12
14
R2
1. NaOH
N
N
n
Mes
Ph
Mes
Si(R1)3
Cl
2. coupling
O
NH
MeO
Ru
Cl
PCy3
7
15
Trisubstituted E-allylsilane 7c was not prepared through
cross-metathesis, but rather from compound 16, through
Scheme 3 General strategy for the preparation of unsaturated O-al-
kyl hydroxamate substrates 7
Synthesis 2012, 44, 1199–1207
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
α-Vinyl Lactams via Nitrenium-Allylsilane Addition
1201
cause substrate protodesilylation.1 Accordingly, trimeth-
ylsilyl-substituted substrates 7a–f were simply treated
with a slight excess of phenyliodine(III) bis(trifluoroace-
tate) in CH2Cl2 at 0 °C (Table 3). In all cases, cyclization
proceeded rapidly and was complete within 30 minutes, at
which point the reactions were treated with a solution of
anhydrous ammonia in methanol to destroy excess PIFA,
neutralize the trifluoroacetic acid generated during this re-
action, and solvolyze any ester addition products.
Table 2 Preparation of Unsaturated O-Alkyl Hydroxamates 7a
O
O
MeO
1. NaOH
MeO
N
n
n
H
R2
Si(R1)3
R2
Si(R1)3
2. coupling
7
14
R1
R2
E/Z ratioc
Entry 14
n
7
Yield
(%)b
1
a
b
c
d
e
f
0
1
2
2
3
4
1
2
3
1
2
3
Me
Me
Me
Me
Me
Me
i-Pr
i-Pr
i-Pr
Ph
H
H
Me
H
H
H
H
H
H
H
H
H
a
b
c
d
e
f
74
85
89
67
88
63
67
36
61
53
47
48
2:1
As is apparent from Table 3, this reaction is characterized
by broad substrate scope and provides efficient access to
4–7- and even 8-membered lactams; only in the case of
azocanone 11f was a by-product formation noted. In this
regard, secondary allylic alcohol 19 is thought to arise
2
>25:1
>25:1d
>25:1
8:1
3
4
5
Table 3 Scope of O-Alkyl Hydroxamate Cyclization: Trimethyl
Allylsilanesa,b
6
10:1
2:1
R2
R2
α
R2
SiMe3
n
7
g
h
i
g
h
i
PIFA
n
β
n
O
N
N
O
NH
8
6:1
–OCOCF3
+
MeO
OMe
O
MeO
SiMe3
9
6:1
7
9
11
10
11
12
j
j
>25:1
>25:1
>25:1
Entry
1
Product
Yield (%)
67
k
l
Ph
k
l
Ph
N
O
OMe
a Conditions: (1) NaOH (4 equiv), EtOH–H2O (1:1), reflux, 2 h; (2)
RCO2H, i-BuOCOCl, Et3N, CH2Cl2, –40 °C → r.t., 12 h, then
MeONH2·HCl (1.2 equiv), Et3N, r.t., 12 h.
11a
b Isolated yield over two steps, after purification by flash chromatog-
raphy.
O
N
2
3
72
72
MeO
c Isomer ratio of determined by 1H NMR spectroscopy.
d Compound 7c was prepared via the route shown in Scheme 4.
11b
O
N
the highly stereoselective Ireland–Claisen rearrangement
of allylic acetate 17 following the method reported by
Cane (Scheme 4).20
MeO
11c
OAc
OH
Ac2O, DMAP
LDA, THF
O
N
4
5
91
87
SiMe3
SiMe3
MeO
–78 °C to r.t.
12 h
Et3N, CH2Cl2
16 h, r.t.
11d
17 (94%)
16
O
O
i-BuOCOCl
Et3N, CH2Cl2
MeO
N
N
O
HO
H
MeO
SiMe3
then
SiMe3
MeONH2⋅HCl
11e
18 (84%, dr >25:1)
7c (89%, dr >25:1)
Scheme 4 Stereoselective synthesis of trisubstituted allylsilane 7c
+
OH
11f (42%);
19 (24%)
6
NH
N
O
O
Having successfully assembled a group of substrates bear-
ing various silyl and alkene substituents and also chain
lengths, our goal was now to validate the feasibility of the
nitrenium ion cyclization. While our alkene oxamidation
methodology calls for the co-addition of trifluoroacetic
acid as a means to improve cyclization efficiency,11a we
opted to forgo this modification in light of its potential to
MeO
MeO
11f
19
a Conditions: 7, PIFA (1.2 equiv), CH2Cl2 (0.15 M), 0 °C; then NH3–
MeOH, 20 min.
b Isolated yield of α-vinyl lactams, after purification by flash chroma-
tography.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1199–1207

1202
D. J. Wardrop et al.
SPECIAL TOPIC
from 7f through direct attack of PIFA at the allylsilane to
form an allyl-λ3-iodane. Nucleophilic displacement of io-
dobenzene with trifluoroacetate and hydrolysis, would
then lead to the observed by-product.21
Table 4 Scope of O-Alkyl Hydroxamate Cyclization: Triisopropyl-
and Triphenylallylsilanesa
R2
PIFA
R2
R2
n
n
n
+
Si(R1)3
O
O
N
N
As indicated in Table 4, the cyclization of triisopropyl and
triphenylsilane substrates 7g–l, although more complex
than that of their trimethylsilyl congeners, led to the wel-
come formation of E-vinylsilanes 20. For example, while
exposure of heptenamide 7h (Table 4, entry 2) to PIFA
lead to the formation of α-vinyl piperidinone 11d and
anti-oxamidation product 21h, the major component of
this reaction proved to be E-vinylsilane 20h, which was
generated in high yield and was readily separable from the
minor products. Similar observations were noted during
the formation of piperidinone 20k (entry 5) and the azep-
anone systems 20i and 20l (entries 3 and 6), but not pyr-
rolidinones (entries 1 and 4). In the case of hexenamides
7g and 7j, cyclization exclusively generated anti-oxami-
dation addition product 21g and α-vinyl lactam 11b, re-
spectively. Notably, the formation of 21g, in common
with the other addition products shown in Table 4, oc-
cured with complete stereocontrol. In light of our previous
observations,11 this process is assumed to proceed with
overall anti stereochemistry.
O
NH
MeO
OH
MeO
MeO
R2
Si(R1)3
7 (R1 = i-Pr, Ph;
R
20 [R2 = H, Si(R1)3]
21 (dr >25:1)
2 = H)
11 (R2 = H)
Product(s) (Yield, %)b
Entry
7
g
H
+
O
N
O
Si(i-Pr)3
N
MeO
1
OH
MeO
11b (15%)
21g (61%)
H
+
O
N
O
N
MeO
Si(i-Pr)3
MeO
OH
2
3
h
Si(i-Pr)3
20h (74%)
21h (12%)
+ 11d (6%)
+
H
N
N
MeO
Si(i-Pr)3
O
O
i
MeO
OH
In order to account for the patterns of divergent, silyl-de-
pendent reactivity highlighted in Tables 3 and 4, we have
formulated the mechanistic rationale shown in Scheme 5.
While we cannot discount the possibility that, in the case
of allyltrimethylsilanes 7a–f, product 11 forms through
direct, concerted SE′-reaction of the nitrenium ion inter-
mediate 8 (pathway A), the stereospecific formation of
anti-addition products 22 in the case of triisopropyl and
triphenylsilanes suggests the intermediacy of aziridinium
ion 9. Upon formation, this strained bicyclic intermediate
appears to have three possible fates: a) ring opening via
concerted ion-pair collapse (pathway B); b) silyl-mediat-
ed ring opening with loss of the trialkylsilyl group (path-
way C); and c) β-eliminative ring opening without loss of
the silyl group and accompanying formation of E-vinylsi-
lanes 20 (pathway D).
Si(i-Pr)3
20i (64%)
21i (18%)
+ 11e (4%)
O
O
N
4
5
j
MeO
11b (54%)
+
N
O
O
N
k
MeO
MeO
SiPh3
20k (58%)
11d (29%)
+
H
N
N
MeO
SiPh3
O
6
l
MeO
OH
In the case of the trimethylsilyl-substituted substrates, at-
tack of trifluoroacetate at the less sterically encumbered
silicon center of 9, or stabilized β-silyl carbocation 10,
and accompanying desilylation appears to be favored over
ion pair collapse at the α-position, as initially anticipated.
Nucleophilic attack at the more crowded silicon center of
triisopropyl and triphenylsilyl-substituted 9 (or 10),22 on
the other hand, is slower and as a result, β-elimination
through proton loss to form ene-type products 20 predom-
inates.23 In contrast to simple alkenes,11a ion pair collapse
while observed in these systems, is not the predominant
pathway, perhaps as a result of the steric influence of the
adjoining β-silyl group. The reason for the lack of vinylsi-
lane formation during the cyclization of substrates 7g and
7j (Table 4, entries 1 and 4) remains unclear and await fur-
ther investigation.
SiPh3
20l (36%)
21l (16%)
+ 11e (17%)
a Conditions: 7, PIFA (1.2 equiv), CH2Cl2 (0.15 M), 0 °C; then NH3–
MeOH, 20 min.
b Isolated yields, after purification by flash chromatography.
In summary, we have successfully developed a versatile
synthetic method for the preparation of 4- to 8-membered
α-vinyl and α-(2-silylvinyl) lactams involving the che-
moselective iodine(III)-mediated oxidative cyclization of
unsaturated O-alkyl hydroxamates which encompass an
allylsilane. Importantly, the outcome of this transforma-
tion can be effectively controlled through variation of the
silyl substitution pattern. While allyltrimethylsilanes un-
dergo ring closure with desilylation to form α-vinyl lac-
Synthesis 2012, 44, 1199–1207
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
α-Vinyl Lactams via Nitrenium-Allylsilane Addition
1203
R2
R1
Allylsilane Cross-Metathesis; General Procedure A
R2
n
To a stirred solution of alkene (1 equiv) and allylsilane (3 equiv) in
anhyd CH2Cl2 (0.5 M) under an atmosphere of N2 at r.t. was added
the Grubbs second-generation catalyst (Grubbs II) (2.5 mol%) in a
single portion. The resulting solution was heated at reflux over-
night, or until TLC (eluent: EtOAc–hexanes, 1:9) showed complete
consumption of starting material, allowed to cool to r.t. and then fil-
tered through a plug of Celite. The filter cake was washed with a
mixture of EtOAc and hexanes (1:9, 20 mL), the combined filtrates
concentrated under reduced pressure, and the resulting residue pu-
rified by flash chromatography over silica gel to provide the desired
product (see Supporting Information for the individual preparation
of the products).
SE'
R1
R1
n
O
Si
N
+
N:
O
A
MeO
8
H
MeO
11
C
[2+1]
– (R1)3SiOTFA
small R1
R1
R2
R1
R1
α
R2
n
Si
β
–OCOCF3
R1
Si
n
O
+
N
ionization
N
H
+
MeO
–OCOCF3
OMe
O
H
R1
10
R1
9
Ester Saponification; General Procedure B
A solution of ester (1 equiv) and aq NaOH (1 M, 4 equiv) in a mix-
ture of EtOH (0.2 M) and H2O (0.2 M) was heated at reflux for 2 h,
or until TLC (eluent: EtOAc–hexanes, 1:10) showed complete con-
sumption of starting material. After cooling to r.t., the reaction mix-
ture was acidified to pH 4–5 with aq HCl (1 M) and quickly
extracted with EtOAc (5 ×). The combined organic extracts were
then dried (Na2SO4), filtered, and concentrated under reduced pres-
sure. The resulting residue was purified by flash chromatography
over silica gel to afford the desired product (see Supporting Infor-
mation for the individual preparation of the products).
SN2
R2
D
B
– TFA
large R1
R2
n
n
R1
Si
O
O
N
N
R1
OTFA R1
R1
Si
MeO
MeO
R1
R1
22
20
Scheme 5
Mechanistic rationale for divergent, silyl-dependent
Amide Coupling; General Procedure C
aziridinium ion ring opening
To a stirred solution of carboxylic acid (1 equiv) in anhyd CH2Cl2
(0.12 M) under an atmosphere of N2 at –40 °C (CO2/MeCN) was
added i-BuOCOCl (1.05 equiv) and Et3N (1 equiv). After stirring
for 10 min, the cold bath was removed and the reaction mixture
stirred for 12 h at r.t., or until TLC (eluent: EtOAc–hexanes, 1:8)
showed complete consumption of starting material. MeONH2·HCl
(1 equiv) and Et3N (1 equiv) were then added and the mixture stirred
for a further 12 h before being quenched with aq HCl (1 M). The bi-
phasic mixture was extracted with EtOAc (3 ×) and the combined
organic extracts were dried (Na2SO4), filtered, and concentrated un-
der reduced pressure. The resulting residue was purified by flash
chromatography over silica gel to provide the desired product (see
Supporting Information for the individual preparation of the prod-
ucts).
tams, the corresponding triisopropyl and triphenylsilanes
cyclize without loss of the larger silyl group to form E-vi-
nylsilanes with excellent stereoselectivity. The α-vinyl N-
alkoxylactams, and corresponding NH lactams,24 avail-
able through these divergent transformations are valuable
building blocks for the preparation of complex natural
products.25 Application of our methodology in this con-
text is in progress and will be reported in due course.
All nonaqueous reactions were carried out in oven- or flame-dried
glassware under an atmosphere of dry nitrogen, unless otherwise
noted. Except as otherwise indicated, all reactions were magnetical-
ly stirred and monitored by analytical TLC using Merck pre-coated
silica gel plates with F254 indicator. Visualization was accomplished
by UV light and/or KMnO4 solution. Flash column chromatography
was performed according to the method of Still26 using silica gel 60
(mesh 230–400) supplied by E. Merck. Yields refer to chromato-
graphically and spectrographically pure compounds, unless other-
wise noted. CH2Cl2 and Et3N were distilled from CaH2 under an
atmosphere of dry N2. Sat. solutions of ammonia in MeOH (NH3–
MeOH) were prepared by bubbling anhyd gaseous NH3 through
cold (0 °C), anhyd MeOH for 20 min. Phenyliodine(III) bis(trifluo-
roacetate) [PIFA, PhI(OTFA)2)] was prepared from PhI(OAc)2 us-
ing the method reported by Loudon.27 All other reagents and
starting materials, unless otherwise noted, were purchased from
commercial vendors and used without further purification. All melt-
ing points were determined in unsealed Pyrex capillaries with a
Thomas Hoover Unimelt melting point apparatus and are uncorrect-
ed. IR spectra were recorded as thin films on NaCl plates using an
ATI Mattson Genesis series FTIR spectrophotometer. 1H NMR and
13C NMR spectra were recorded on a Bruker Avance 400 (400 MHz
1H, 100 MHz 13C) or a Bruker Avance 500 (500 MHz 1H, 125 MHz
13C) spectrometer. Chemical shift values (δ) are reported in ppm rel-
ative to residual CHCl3 (δ = 7.27 for 1H; δ = 77.23 for 13C). High-
resolution electrospray ionization (HRMS-ESI) mass spectra were
obtained on a Micro Mass QTOF II instrument at the University of
Illinois Research Resources Center.
Oxidative Cyclization of O-Alkyl Hydroxamates; General Pro-
cedure D
To a stirred solution of unsaturated O-alkyl hydroxamate (1.0
equiv) in anhyd CH2Cl2 (0.1 M) at 0 °C was added solution of fresh-
ly prepared PIFA (1.2 equiv) in CH2Cl2 (0.1 M) via a cannula. After
stirring for 30 min, or until TLC (eluent: EtOAc–hexanes, 1:1)
showed complete consumption of starting material, a sat. solution of
ammonia in anhyd MeOH (2 mL/mmol) was added, the reaction al-
lowed to warm to r.t., and stirred for 15 min. The resulting mixture
was concentrated under reduced pressure and purified by flash chro-
matography over silica gel to yield the observed products.
(±)-1-Methoxy-4-vinylazetidin-2-one (11a)
Following General Procedure D, reaction of 7a (400 mg, 1.78
mmol) with PIFA (921 mg, 2.14 mmol) in CH2Cl2 (29 mL) fol-
lowed by addition of sat. methanolic ammonia (11 mL) furnished a
crude product, which was purified by flash chromatography over
silica gel (EtOAc–hexanes, 1:1) to provide the title compound as a
colorless oil (179 mg, 67%).
IR (film): 2939, 1776, 1461, 1429, 1313, 1193, 1043 cm–1.
1H NMR (400 MHz, CDCl3): δ = 5.93–5.84 (apt ddd, J = 18.8, 10.4,
8.4 Hz, 1 H), 5.50–5.45 (d, J = 17.9 Hz, 1 H), 5.35–5.32 (d, J = 10.3
Hz, 1 H), 4.33–4.29 (m, 1 H), 3.80 (s, 3 H), 2.96–2.91 (dd, J = 13.7,
7.9 Hz, 1 H), 2.51–2.48 (dd, J = 13.7, 2.4 Hz, 1 H).
13C NMR (100 MHz, CDCl3): δ = 163.6, 135.4, 120.6, 64.3, 59.1,
39.2.
© Georg Thieme Verlag Stuttgart · New York
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D. J. Wardrop et al.
SPECIAL TOPIC
HRMS-EI: m/z calcd for C6H9NO2 + Na [M + Na]+: 150.1309;
found: 150.1314.
2.56–2.51 (m, 1 H), 5.47–2.42 (m, 1 H), 2.04–1.99 (m, 1 H), 1.90–
1.85 (m, 1 H), 1.75–1.69 (m, 3 H), 1.62–1.57 (m, 1 H).
13C NMR (125 MHz, CDCl3): δ = 174.2, 135.8, 116.9, 77.2, 64.3,
62.5, 35.9, 32.8, 25.1, 23.1.
HRMS-EI: m/z calcd for C10H17NO2 + Na [M + Na]+: 206.2372;
found: 206.2380.
(±)-1-Methoxy-5-vinylpyrrolidin-2-one (11b)
Following General Procedure D, reaction of 7b (250 mg, 1.05
mmol) with PIFA (541 mg, 1.26 mmol) in CH2Cl2 (17.5 mL) fol-
lowed by addition of sat. methanolic ammonia (6.6 mL) furnished a
crude product, which was purified by flash chromatography over
silica gel (EtOAc–hexanes, 1:1) to provide the title compound as a
colorless oil (124 mg, 72%).
(±)-1-Methoxy-8-vinylazocan-2-one (11f) and (±)-7-Hydroxy-N-
methoxynon-8-enamide (19)
Following General Procedure D, reaction of 7f (150 mg, 0.54
mmol) with PIFA (276 mg, 0.64 mmol) in CH2Cl2 (9 mL) followed
by addition of sat. methanolic ammonia (3.4 mL) furnished a crude
product, which was purified by flash chromatography over silica gel
(EtOAc–hexanes, 1:1) to provide the title compounds 11f (47 mg,
42%) and 20 (29 mg, 24%) as colorless oils.
IR (film): 3413, 3081, 2981, 2939, 1720, 1425, 1247, 1058 cm–1.
1H NMR (400 MHz, CDCl3): δ = 5.79–5.73 (apt ddd, J = 17.0, 12.2,
5.2 Hz, 1 H), 5.35–5.34 (dd, J = 17.0, 1.0, 1.0 Hz, 1 H), 5.25–2.23
(d, J = 10.0 Hz, 1 H), 4.17–4.11 (apt ddd, J = 7.7, 7.2, 7.2 Hz, 1 H),
3.75 (s, 3 H), 2.39–2.17 (m, 3 H), 1.78–1.75 (m, 1 H).
13C NMR (100 MHz, CDCl3): δ = 171.7, 136.6, 119.2, 63.4, 60.9,
27.1, 22.9.
HRMS-EI: m/z calcd for C17H11NO2 + Na [M + Na]+: 164.1575;
found: 164.1573.
11f
IR (film): 2931, 2859, 1668, 1423, 1232, 1049 cm–1.
1H NMR (400 MHz, CDCl3): δ = 5.96–5.88 (app ddd, J = 17.2,
10.5, 4.7 Hz, 1 H), 5.31–5.25 (m, 2 H), 4.49–4.44 (m, 1 H), 3.77 (s,
3 H), 2.57–2.41 (m, 2 H), 2.04–1.91 (m, 1 H), 1.91–1.83 (m, 1 H),
1.76–1.68 (m, 4 H), 1.63–1.57 (m, 1 H).
13C NMR (100 MHz, CDCl3): δ = 174.2, 135.8, 116.9, 64.3, 62.5,
32.8, 25.1, 23.1.
(±)-1-Methoxy-5-methyl-5-vinylpyrrolidin-2-one (11c)
Following General Procedure D, reaction of 7c (75 mg, 0.43 mmol)
with PIFA (222 mg, 0.52 mmol) in CH2Cl2 (7 mL) followed by ad-
dition of sat. methanolic ammonia (2.7 mL) furnished a crude prod-
uct, which was purified by flash chromatography over silica gel
(EtOAc–hexanes, 1:1) to provide the title compound as a colorless
oil (60 mg, 78%).
HRMS-EI: m/z calcd for C10H17NO2 + Na [M + Na]+: 206.2372;
found: 206.2380.
19
IR (film): 3342, 2958, 2919, 1716, 1683, 1457, 1430, 1378, 1257,
1170 cm–1.
1H NMR (500 MHz, CDCl3): δ = 5.87–5.82 (dd, J = 17.4, 10.7 Hz,
1 H), 5.26–5.20 (d, J = 10.5 Hz, 1 H), 5.18–5.14 (d, J = 4.2 Hz, 1
H), 3.85 (s, 3 H), 2.37–2.28 (m, 2 H), 2.03–1.91 (m, 1 H), 1.89–1.84
(m, 1 H), 1.44 (s, 3 H).
13C NMR (125 MHz, CDCl3): δ = 171.2, 140.1, 114.2, 64.8, 64.5,
30.4, 26.4, 22.7.
HRMS-EI: m/z calcd for C8H13NO2 + Na [M + Na]+: 178.1954;
found: 178.1956.
IR (film): 3031, 2934, 2866, 1660, 1421 cm–1.
1H NMR (400 MHz, CDCl3): δ = 5.96–5.88 (app ddd, J = 17.2,
10.5, 4.7 Hz, 1 H), 5.31–5.25 (m, 2 H), 4.49–4.44 (m, 1 H), 3.77 (s,
3 H), 2.57–2.41 (m, 2 H), 2.04–1.91 (m, 1 H), 1.91–1.83 (m, 1 H),
1.76–1.68 (m, 4 H), 1.63–1.57 (m, 1 H).
13C NMR (100 MHz, CDCl3): δ = 173.3, 135.4, 117.1, 69.4, 64.4,
62.5, 35.6, 29.9, 24.9, 22.4.
HRMS-EI: m/z calcd for C10H19NO3 + Na [M + Na]+: 224.2525;
found: 224.2518.
(±)-1-Methoxy-5-vinylpyrrolidin-2-one (11b) and (R*)-1-Hy-
droxy-(R*)-2-(triisopropylsilyl)ethyl-1-methoxypyrrolidin-2-
one (21g)
Following General Procedure D, reaction of 7g (125 mg, 0.39
mmol) with PIFA (201 mg, 0.47 mmol) in CH2Cl2 (7 mL) followed
by addition of sat. methanolic ammonia (2.4 mL) furnished a crude
product, which was purified by flash chromatography over silica gel
(EtOAc–hexanes, 1:1) to provide 11b (9.6 mg, 15%) and 21g (75.2
mg, 61%) as colorless oils.
(±)-1-Methoxy-6-vinylpiperidin-2-one (11d)
Following General Procedure D, reaction of 7d (120 mg, 0.52
mmol) with PIFA (269 mg, 0.63 mmol) in CH2Cl2 (9 mL) followed
by addition of sat. methanolic ammonia (3.3 mL) furnished a crude
product, which was purified by flash chromatography over silica gel
(EtOAc–hexanes, 1:1) to provide the title compound as a colorless
oil (84 mg, 91%).
IR (film): 2937, 1668, 1444, 1398, 1332, 1285, 1141, 1070, 967 cm–1.
1H NMR (500 MHz, CDCl3): δ = 5.85–5.79 (apt ddd, J = 24.0, 10.3,
7.0 Hz, 1 H), 5.82–5.23 (m, 2 H), 4.25 (m, 1 H), 3.73 (s, 3 H), 2.46–
2.43 (m, 2 H), 2.04–1.98 (m, 1 H), 1.86–1.79 (m, 2 H), 1.69–1.66
(m, 1 H).
13C NMR (125 MHz, CDCl3): δ = 167.7, 163.7, 117.8,62.7, 62.1,
33.3, 30.4, 18.4.
21g
IR (film): 3424, 2939, 2865, 1695, 1463, 1272, 1060, 883 cm–1.
1H NMR (400 MHz, CDCl3): δ = 3.93 (m, 1 H), 3.82 (s, 3 H), 3.71–
3.66 (m, 1 H), 2.71 (br s, 1 H), 2.39–2.22 (m, 1 H), 2.15–2.07 (m, 1
H), 1.95 (m, 1 H), 1.76–1.68 (m, 1 H), 1.04 (m, 21 H), 0.76 (m, 2 H).
13C NMR (100 MHz, CDCl3): δ = 170.7, 73.1, 66.3, 62.4, 61.9, 27.1,
19.0 (6 C), 12.8, 11.5 (3 C).
HRMS-ESI: m/z calcd for C8H13NO2 + Na [M + Na]+: 178.1841;
found: 178.1838.
HRMS-EI: m/z calcd for C16H34NO3Si [M + H]+: 316.2308; found:
316.2312.
(±)-1-Methoxy-7-vinylazepan-2-one (11e)
Following General Procedure D, reaction of 7e (122 mg, 0.46
mmol) with PIFA (237 mg, 0.55 mmol) in CH2Cl2 (7.6 mL) fol-
lowed by addition of sat. methanolic ammonia (2.9 mL) furnished a
crude product, which was purified by flash chromatography over
silica gel (EtOAc–hexanes, 1:1) to provide the title compound as a
colorless oil (77 mg, 87%).
(±)-1-Methoxy-6-vinylpiperidin-2-one (11d), (±)-6-[(E)-2-(Tri-
isopropylsilyl)vinyl]-1-methoxypiperidin-2-one (20h), and (R*)-
6-[(R*)-1-Hydroxy-2-(triisopropylsilyl)ethyl]-1-methoxypiperi-
din-2-one (21h)
Following General Procedure D, reaction of 7h (110 mg, 0.35
mmol) with PIFA (181 mg, 0.42 mmol) in CH2Cl2 (6 mL) followed
by addition of sat. methanolic ammonia (2.2 mL) furnished a crude
product, which was purified by flash chromatography over silica gel
IR (film): 2930, 2860, 1727, 1667, 1447, 1285, 1047 cm–1.
1H NMR (500 MHz, CDCl3): δ = 5.93–5.88 (apt ddd, J = 17.2, 10.6,
5.8 Hz, 1 H), 5.31–5.26 (m, 2 H), 4.47–4.44 (m, 1 H), 3.77 (s, 3 H),
Synthesis 2012, 44, 1199–1207
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
α-Vinyl Lactams via Nitrenium-Allylsilane Addition
1205
(EtOAc–hexanes, 1:1) to provide 11d (4 mg, 6%), 20h (81 mg,
74%), and 21h (15 mg, 12%) as colorless oils.
(±)-1-Methoxy-5-vinylpyrrolidin-2-one (11b)
Following General Procedure D, reaction of 7j (256 mg, 0.65
mmol) with PIFA (312 mg, 0.73 mmol) in CH2Cl2 (5.1 mL) fol-
lowed by addition of sat. methanolic ammonia (3.8 mL) furnished a
crude product, which was purified by flash chromatography over
silica gel (EtOAc–hexanes, 1:1) to provide the title compound as a
colorless oil (36 mg, 54%). For analytical and spectral data, see
above.
20h
IR (film): 2939, 2856, 1690, 1463, 1272, 1062, 896 cm–1.
1H NMR (500 MHz, CDCl3): δ = 6.06–6.01 (dd, J = 18.8, 6.6 Hz, 1
H), 5.80–5.77 (dd, J = 18.8, 1.0 Hz, 1 H), 4.27–4.26 (m, 1 H), 3.75
(s, 3 H), 2.48–2.45 (app ddd, J = 6.4, 6.4, 2.4 Hz, 2 H), 2.05–2.00
(m, 1 H), 1.86–1.79 (m, 2 H), 1.72–1.65 (m, 1 H), 1.10–0.99 (m, 21
H).
13C NMR (125 MHz, CDCl3): δ = 167.8, 146.1, 127.6, 65.4, 62.1,
33.4, 30.8, 19.2, 18.6 (6 C), 11.1 (3 C).
(±)-1-Methoxy-6-vinylpiperidin-2-one (11d) and (±)-(E)-1-
Methoxy-6-[2-(triphenylsilyl)vinyl]piperidin-2-one (20k)
Following General Procedure D, reaction of 7k (158 mg, 0.38
mmol) with PIFA (196 mg, 0.46 mmol) in CH2Cl2 (6.4 mL) fol-
lowed by addition of sat. methanolic ammonia (2.4 mL) furnished a
crude product, which was purified by flash chromatography over
silica gel (EtOAc–hexanes, 1:15) to provide 11d (27 mg, 29%) and
20k (113 mg, 58%) as colorless oils.
HRMS-EI: m/z calcd for C17H33NO2Si [M + H]+: 313.2367; found:
313.2359.
21h
IR (film): 3249, 2939, 2856, 1742, 1569, 1463, 1272, 1062 cm–1.
20k
1H NMR (500 MHz, CDCl3): δ = 3.82 (app ddd, J = 18.2, 3.8, 3.8
Hz, 1 H), 3.67 (s, 3 H), 3.66 (m, 1 H), 2.20–2.17 (m, 2 H), 1.64–1.39
(m, 4 H), 0.92 (m, 21 H), 0.82–0.75 (m, 2 H).
13C NMR (125 MHz, CDCl3): δ = 172.4, 71.5, 70.2, 67.8, 29.1, 28.7
(3 C), 19.9, 19.1, 18.6 (6 C), 13.5.
HRMS-EI: m/z calcd for C17H35NO3Si + Na [M + Na]+: 352.5402;
found: 352.5399.
IR (film): 3403, 3066, 30.46, 2958, 2929, 2858, 1725, 1666, 1461,
1427, 1274, 1124 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.52–7.51 (m, 6 H), 7.39–7.27 (m,
9 H), 6.46–6.43 (dd, J = 7.0. 0.5, 0.5 Hz, 1 H), 6.10–6.06 (app ddd,
J = 18.5, 0.5, 0.5 Hz, 1 H), 5.37 (app ddd, J = 17, 0.8, 0.8 Hz, 1 H),
3.72 (s, 3 H), 2.44–2.36 (m, 2 H), 2.34–2.27 (m, 2 H), 2.23–2.19 (m,
2 H), 1.83–1.761 (m, 2 H).
13C NMR (125 MHz, CDCl3): δ = 174.3, 146.1, 136.1 (6 C), 135.3
(3 C), 129.9 (3 C), 128.4 (6 C), 127.6, 126.1, 65.4, 62.1, 33.4, 30.8.
(±)-1-Methoxy-7-vinylazepan-2-one (11e), (±)-7-[(E)-2-(Triiso-
propylsilyl)vinyl]-1-methoxyazepan-2-one (20i), and (R*)-7-
[(R*)-1-Hydroxy-2-(triisopropylsilyl)ethyl]-1-methoxyazepan-
2-one (21i)
HRMS-ESI: m/z calcd for C26H27NO2Si + Na [M + Na]+: 437.1913;
found: 437.1918.
Following General Procedure D, reaction of 7i (158 mg, 0.48 mmol)
with PIFA (248 mg, 0.58 mmol) in CH2Cl2 (8 mL) followed by ad-
dition of sat. methanolic ammonia (3.0 mL) furnished a crude prod-
uct, which was purified by flash chromatography over silica gel
(EtOAc–hexanes, 1:1) to provide 11e (6.5 mg, 4%), 20i (115 mg,
64%), and 21i (34 mg, 18%) as colorless oils.
(±)-1-Methoxy-7-vinylazepan-2-one (11e), (±)-(E)-1-Methoxy-
7-[2-(triphenylsilyl)vinyl]azepan-2-one (20l), and (R*)-7-[(R*)-
1-Hydroxy-2-(triphenylsilyl)ethyl]-1-methoxyazepan-2-one
(21l)
Following General Procedure D, reaction of 7l (129 mg, 0.31 mmol)
with PIFA (160 mg, 0.37 mmol) in CH2Cl2 (6.0 mL) followed by
addition of sat. methanolic ammonia (1.9 mL) furnished a crude
product, which was purified by flash chromatography over silica gel
(EtOAc–hexanes, 1:1) to provide 11e (10 mg, 17%), 20l (50 mg,
36%), and 21l (23 mg, 16%) as colorless oils.
20i
IR (film): 3457, 2939, 2863, 1737, 1668, 1461, 1234, 1197, 1047,
997, 892 cm–1.
1H NMR (500 MHz, CDCl3): δ = 6.09–6.06 (dd, J = 19.1, 3.8 Hz, 1
H), 5.82–5.78 (dd, J = 19.1, 3.8 Hz, 1 H), 4.29–4.25 (m, 1 H), 3.77
(s, 3 H), 2.55–2.51 (app ddd, J = 8.6, 6.0, 1.2 Hz, 1 H), 2.43–2.37
(app ddd, J = 14.5, 11.6, 1.9 Hz, 1 H), 2.11–2.07 (m, 1 H), 1.91–
1.86 (app ddt, J = 12.0, 6.5, 3.5, 3.5 Hz, 1 H), 1.77–1.72 (m, 2 H),
1.68–1.65 (m, 1 H), 1.59–1.54 (m, 1 H).
13C NMR (125 MHz, CDCl3): δ = 172.4, 144.8, 126.4, 66.4, 62.3,
35.9, 32.8, 25.2, 23.2, 19.1 (6 C), 11.1 (3 C).
HRMS-ESI: m/z calcd for C18H35NO2Si + Na [M + Na]+: 348.2335;
found: 348.2335.
20l
IR (film): 3068, 2956, 2929, 2858, 1725, 1664, 1461, 1429, 1274,
1110 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.55–7.36 (m, 15 H), 6.48–6.44
(dd, J = 19.1, 3.8 Hz, 1 H), 6.16–6.12 (dd, J = 19.1, 3.8 Hz, 1 H),
4.56 (m, 1 H), 3.75 (s, 3 H), 2.55–2.51 (app ddd, J = 8.6, 6.0, 1.2 Hz,
1 H), 2.43–2.37 (app ddd, J = 14.5, 11.6, 1.9 Hz, 1 H), 2.11–2.07
(m, 1 H), 1.91–1.86 (app ddt, J = 18.0, 6.5, 3.5, 3.5 Hz, 1 H), 1.77–
1.72 (m, 2 H), 1.68–1.65 (m, 1 H).
13C NMR (125 MHz, CDCl3): δ = 172.5, 148.6, 136.1 (6 C), 135.3
(3 C), 129.9 (3 C), 128.4 (6 C), 126.4, 66.2, 62.4, 35.9, 32.6, 25.3,
23.1.
HRMS-ESI: m/z calcd for C27H29NO2Si + Na [M + Na]+: 450.1865;
found: 450.1868.
21i
FTIR (film): 3407, 2939, 2863, 1644, 1461, 1045, 895 cm–1.
1H NMR (500 MHz, CDCl3): δ = 4.37–4.35 (app ddd, J = 10.0, 3.5,
3.5 Hz, 1 H), 3.87 (s, 3 H), 3.66–3.64 (app ddd, J = 9.0, 2.5, 2.5 Hz,
1 H), 2.58–2.52 (app ddd, J = 14.5, 11.6, 1.9 Hz, 1 H), 2.46–2.41
(app ddd, J = 14.5, 11.6, 1.9 Hz, 1 H), 2.00–1.93 (m, 1 H), 1.88–
1.80 (m, 1 H), 1.75–1.60 (m, 2 H), 1.59–1.52 (m, 1 H), 1.13–1.04
(m, 21 H), 1.01–0.96 (dd, J = 14.5, 10.0 Hz, 1 H), 0.79–0.75 (dd,
J = 15.0, 3.5 Hz, 1 H).
13C NMR (125 MHz, CDCl3): δ = 173.0, 70.8, 69.3, 63.6, 35.1, 28.9,
26.6, 25.2, 23.2, 19.0 (6 C), 11.4 (3 C).
HRMS-EI: m/z calcd for C18H38NO3Si [M + H]+: 345.2630; found:
345.2621.
21l
IR (film): 3407, 2939, 2863, 1644, 1461, 1045 cm–1.
1H NMR (500 MHz, CDCl3): δ = 7.61–7.27 (m, 15 H), 4.15–4.10
(m, 1 H), 3.75 (s, 3 H), 3.65–3.58 (m, 1 H), 2.33–2.30 (m, 2 H),
1.82–1.75 (m, 4 H), 1.68–1.52 (m, 4 H).
13C NMR (125 MHz, CDCl3): δ = 173.0, 146.1, 136.1 (6 C), 135.3
(3 C), 129.9 (3 C), 128.4 (6 C), 127.6, 69.3, 63.6, 35.1, 26.6, 25.2,
23.2.
HRMS-EI: m/z calcd for C27H31NO3Si + Na [M + Na]+: 468.1971;
found: 468.1969.
© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1199–1207

1206
D. J. Wardrop et al.
SPECIAL TOPIC
Interscience: Hoboken N.J., 2004, 593. (g) Borodkin, G. I.;
Shubin, V. G. Russ. Chem. Rev. 2008, 77, 419.
(h) Kikugawa, Y. Heterocycles 2009, 78, 571.
Acknowledgment
This work was supported by National Institutes of Health
(GM59517).
(11) (a) Wardrop, D. J.; Bowen, E. G.; Forslund, R. E.; Sussman,
A. D.; Weerasekera, S. L. J. Am. Chem. Soc. 2009, 132,
1188. (b) Bowen, E. G.; Wardrop, D. J. Org. Lett. 2010, 12,
5330. (c) Wardrop, D. J.; Bowen, E. G. Org. Lett. 2011, 13,
2376.
Supporting Information for this article is available online at
http://www.thieme-connect.com/ejournals/toc/synlett.onmorinftIangoimnuSpinorttfoIangiStupor
(12) For the generation of nitrenium ions through iodine(III)-
mediated N-oxidation, see: (a) Wardrop, D. J.; Basak, A.
Org. Lett. 2001, 3, 1053. (b) Wardrop, D. J.; Zhang, W. Org.
Lett. 2001, 3, 2353. (c) Wardrop, D. J.; Burge, M. S.; Zhang,
W.; Ortiz, J. A. Tetrahedron Lett. 2003, 44, 2587.
(d) Wardrop, D. J.; Landrie, C. L.; Ortiz, J. A. Synlett 2003,
1352. (e) Wardrop, D. J.; Burge, M. S. J. Org. Chem. 2004,
69, 1230. (f) Wardrop, D. J.; Zhang, W. M.; Landrie, C. L.
Tetrahedron Lett. 2004, 45, 4229. (g) See reference 10h.
(h) See reference 11.
References
(1) For reviews of the chemistry of allylsilanes, see: (a) Colvin,
E. W. Chem. Soc. Rev. 1978, 7, 15. (b) Hosomi, A. Acc.
Chem. Res. 1988, 21, 200. (c) Fleming, I.; Dunogués, J.;
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© Georg Thieme Verlag Stuttgart · New York
Synthesis 2012, 44, 1199–1207