Free-radical carbo-oximation of olefins and subsequent radical-ionic cascades

Article abstract of DOI:10.1016/j.tet.2013.09.051

A sequential carbo-formylation cascade has been developed, involving a free-radical carbo-oximation process, followed by the hydrolysis of the oxime ether. For this purpose, we designed a new SEM O-protected sulfonyl oxime, which enable both rapid radical addition and hydrolysis under mild conditions. The resulting aldehyde-esters were then engaged in various nucleophilic cascades, such as Sakurai allylations or domino-Mukaiyama aldol condensation/ lactonizations. Addition of an amine and TMSCN similarly led after Strecker reaction/lactamization to α-cyano-piperidinones in good overall yield. Finally, a Pictet-Spengler/lactamization sequence was devised, which open a new entry toward the tricyclic core of eburnan alkaloids.

Full text of DOI:10.1016/j.tet.2013.09.051

Tetrahedron 69 (2013) 10073e10080
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Free-radical carbo-oximation of olefins and subsequent radical-ionic
cascades
*
ꢀ ꢀ
Yannick Landais , Frederic Robert, Edouard Godineau, Laurent Huet, Nachiket Likhite
ꢀ
University of Bordeaux, Institute of Molecular Sciences, UMR-CNRS-5255, 351 cours de la liberation, 33405 Talence Cedex, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 August 2013
Received in revised form 13 September 2013
Accepted 17 September 2013
Available online 24 September 2013
A sequential carbo-formylation cascade has been developed, involving a free-radical carbo-oximation
process, followed by the hydrolysis of the oxime ether. For this purpose, we designed a new SEM O-
protected sulfonyl oxime, which enable both rapid radical addition and hydrolysis under mild conditions.
The resulting aldehyde-esters were then engaged in various nucleophilic cascades, such as Sakurai al-
lylations or domino-Mukaiyama aldol condensation/lactonizations. Addition of an amine and TMSCN
similarly led after Strecker reaction/lactamization to a-cyano-piperidinones in good overall yield. Finally,
a PicteteSpengler/lactamization sequence was devised, which open a new entry toward the tricyclic core
of eburnan alkaloids.
Keywords:
Radical
Multicomponent reactions
Oximes
Ó 2013 Elsevier Ltd. All rights reserved.
Mukaiyama aldol
PicteteSpengler reaction
1. Introduction
R
Addition of functionalized carbon fragments across the olefinic
p-system offers a straightforward access to valuable intermediates
for organic synthesis. Such a transformation may be handled
through a multicomponent approach, using organometallic cataly-
sis.1 Several studies have thus been reported, although their scope of
application is restricted by the nature of the added fragments.1 Free-
radical multicomponent reactions (MCR) are more flexible and fulfill
some of the stringent criteria for an efficient carbo-functionalization
of olefins.2 Radical MCRs have thus attracted a considerable
Fig. 1. Free-radical 3-component processes with sulfones.
allylsulfones5d,7,9 hold a prominent place, due to the efficient
attention. Addition of carbon-radical species across the p-system of
b
-fragmentation of the sulfonyl moiety.10 Sulfones also allow the
electron-deficient olefins is a well documented and reliable trans-
incorporation of other R3 substituents on the olefinic backbone
(CN, SPh, Cl, N3, etc..).7,11
formation.3 In contrast, it is only recently that addition of carbon
fragments across the
p-bond of non-activated olefins through
Pioneering studies by Kim and co-workers12 showed that sulfonyl
oximes are also excellent radical acceptors, enabling the in-
corporation of an oxime onto a carbon framework. Based on this
work, we recently developed a free-radical formal [2þ2þ2]-process
involving sulfonyl oximes as electrophilic radical traps.13 Addition, of
a nucleophilic alkyl radical or an allylzinc species onto the oxime,
issued from the 3-component reaction, led to the one-pot formation
of 5,6-disubstituted piperidinones in good yields and high diaster-
eoselectivities. The present work describes our studies on the gen-
eralization of this carbo-oximation of olefins as a formal carbo-
formylation process. Carbo-formylation of an olefin under radical
conditions has been described by Ryu et al. using carbon monoxide
as the radical trap.14 The use of Kim’s sulfonyl oxime 1a constitutes
a more practical surrogate to toxic CO,12,15 which generally requires
free-radical pathways has received intense scrutiny, resulting in
the description of useful transformations, such as for instance
carbo-alkynylation,4 carbo-allylation,2,5 and carbo-alkenylation of
olefins.5d,e,6,7 These processes also illustrate the importance of the
influence of polar effects in free-radical MCRs.2c Such reactions
proceed through the preliminary addition of an electron-poor radi-
cal issued from A to the less hindered end of an olefin B, forming
a new nucleophilic radical, which can then be trapped by an
electrophilic partner C (Fig. 1).7 Various electrophilic species may
be envisioned, but sulfones including vinyl-,7,8 alkynyl-,4,7 and
* Corresponding author. Tel.: þ33 5 40002289; fax: þ33 5 40006286; e-mail
address: y.landais@ism.u-bordeaux1.fr (Y. Landais).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.09.051

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Y. Landais et al. / Tetrahedron 69 (2013) 10073e10080
relatively high pressure, and therefore specific autoclave equip-
ment.14 We report herein the synthesis and the use in multicom-
ponent reactions of the new SEM-protected sulfonyl oxime 1b,
which enables facile hydrolysis of the oxime under mild conditions.
We finally describe the post-functionalization of the carbo-
formylation products, which provides a rapid access to lactones, af-
ter Mukaiyama aldol or Sakurai allylation reactions or more complex
piperidinones using PicteteSpengler processes (Scheme 1).
reproducible yields of the 3-component adducts were obtained
(60e80%). The final oximes 4aet were easily isolated through
chromatography over silica gel. A broad variety of substituents on
the olefin is compatible with the reaction conditions, including
electron-rich olefins, such as allylsilanes (3f, entry 7) and enol
ethers (3b, entry 2,6,8), but also simple alkyl olefins (3ced, entry
3e4). Trisubstituted olefins also reacted well leading to tertiary
formaldoximes (entries 10e12, 20). In contrast, vinyl-phthalimide
3e (entry 5) led to a poor yield. The scope of the xanthate pre-
cursors was investigated and functional groups, such as esters, ke-
tones, and thioesters, all provided the desired products in good
yields showcasing the tolerance of the process towards the nature of
the xanthate.16 Activated esters bearing good leaving groups, such
as C6F5O performed also well under the reaction conditions (entry
6). Although the present work based on phenylsulfonyl oximes
generates undesired stannylated by-products, this procedure was
found more efficient, in terms of yields, than the one using ethyl-
sulfonyl oximes, which does not require the use of (Bu3Sn)2.7,13a
The reaction was extended to new sulfonyl oximes 7aeb, readily
available from the corresponding a-sulfonyl nitrile 5. The treatment
of the latter with isoamyl nitrite under basic conditions12,17 led to
the desired oxime 6, which was O-protected18 to afford 7aeb in
good overall yield (Scheme 2). The carbo-oximation of vinyl pivalate
3b under the conditions described above, with oxime ethers 7aeb
and iodoester 8 gave the desired nitriles 9aeb in excellent yields.
Scheme 1. 3-Component carbo-oximation and post-functionalization.
2. Results and discussions
The 3-component carbo-oximation process was first carried out
using Kim’s sulfonyl oxime 1a12a (2 equiv), an excess of the olefin 3
(5 equiv), a xanthate precursor 2 (1e1.2 equiv), and (Bu3Sn)2
(1.5 equiv) in benzene (degassed) as a solvent. The reaction was
initiated using di-tert-butylhyponitrite (DTBHN) (10 mol %). The
results are summarized in Table 1 below. Generally good and
Table 1
Free-radical carbo-oximation of olefins with sulfonyl oxime 1a
Entry Xanthate 2 R1
Olefin R2
R3
Product Yielda
1
2
3
4
5
6
7
8
2a
2a
2b
2a
2a
2cb
2d
2d
2d
2d
2d
2d
2e
2e
2e
2e
2e
2e
2e
2e
PhO
PhO
EtO
PhO
PhO
3a
3b
3c
3d
3e
OAc
OPiv
C6H13
e(CH2)5e
NPht
OPiv
CH2SiMe3
OPiv
Me 4a
72
70
64
73
32
64
60
61
60
68
67
61
68
71
71
74
66
69
58
72
Scheme 2. Synthesis of oximes 7aeb and their 3-CR reactions.
H
H
4b
4c
4d
4e
4f
4g
4h
4i
Hydrolysis of oxime ethers (Bn, Me) often requires rather harsh
conditions, producing the desired aldehyde along with the reactive
hydroxylamine H2NOR0 (Scheme 3, pathway (a)). As the reaction is
formally reversible, excess aqueous formaldehyde is generally
employed to trap H2NOR0 and shift the equilibrium in the desired
direction.12,15 Although these conditions have a broad scope, the
presence of large quantities of aqueous formaldehyde may not be
compatible with other functional groups in the substrate. We thus
designed a second generation of oxime ethers, which could be
converted into the corresponding aldehyde under mild conditions,
without the recourse to aqueous formaldehyde (Scheme 3, path-
way (b)). It was foreseen that the SEM (2-(trimethylSilyl)Ethox-
yMethyl ether) group19 should be well adapted for this purpose. Its
deprotection typically achieved with Brønsted acids, such as TFA20
would produce the desired aldehyde, a silylated derivative, ethyl-
ene (both likely volatile by-products), but also an equivalent of
H
H
H
H
H
(C6F5)O 3b
Me
Me
Me
Me
Me
Me
PhS
PhS
PhS
PhS
PhS
PhS
PhS
PhS
3f
3b
3c
3d
3g
3h
3f
3b
3c
3d
3g
3h
3i
9
C6H13
10
11
12
13
14
15
16
17
18
19
20
e(CH2)5e
e(CH2)4e
Et
CH2SiMe3
OPiv
4j
4k
4l
Et
H
H
H
4m
4n
4o
4p
4q
4r
4s
C6H13
e(CH2)5e
e(CH2)4e
Et
(CH2)3OTBDMS
(CH2)2OTBDMS Me 4t
Et
H
3j
a
Isolated yield after chromatography over silica gel.
The a-bromoester was used instead of the xanthate.
b

Y. Landais et al. / Tetrahedron 69 (2013) 10073e10080
10075
formaldehyde and H2NOH. It was anticipated that formaldehyde
and hydroxylamine would condense to form the formaldoxime,
overall acting as a driving force towards the clean formation of the
desired aldehyde. Trans-oximation between deprotected oxime
and formaldehyde may also occur.
overall yield in six steps from 10 on a multigram scale. Simple O-
protection with SEMCl18 was also performed with readily available
oxime 6 and 16, providing the corresponding SEM-oxime ethers 15
and 17 in excellent yields.
The compatibility of these new oximes toward radical conditions
using tin as a mediator, was tested with the addition of isopropyl
iodide onto oximes 15 and 17. The latter were found to be slightly
morereactivethanthebenzylatedanalogue1a, leadingtothedesired
products 18aeb in good yield in less than 1.5 h. With these results in
hand, the three-component process was then studied using iodide 8
orxanthates2das radicalprecursors, a range ofolefins3 asaboveand
sulfonyl oxime 1b. Better yields were consistently obtained using
2 equiv of oxime (Table 2). The scale-up of the reaction required the
reaction to be performed using a 0.4e0.5 M concentration in iodide
or xanthate, in order to get three-component adducts in good yields.
The reaction conditions were found to be compatible with esters
(entry 2e3, 16, 20), silyl ethers (entry 10), Boc protected amines
(entry 12), but surprisingly, no reactionwas observed when a free OH
group was present in the olefin (entry 11). Similarly, no reaction was
observed with styrenes, vinyl ethers (entry 14), and allylic acetates,
which is surprising as these olefins were shown to be compatible
partners, for instance, in carbo-alkenylation,6 a multicomponent
process run under similar conditions (Scheme 5).
Scheme 3. Hydrolysis of oxime ethers.
We prepared the corresponding sulfonyl oxime 1b using the six-
steps sequence depicted below (Scheme 4).12a The SEM-protected
hydroxylamine 11, which is not commercially available was pre-
pared from N-hydroxyphthalimide 10 in two-steps.21 Formylation
of 11 afforded the formaldoxime ether 12, which was then chlori-
nated to give 13. Introduction of the sulfonyl group was carried out
through a two-steps sequence via the intermediate thioxime ether
14. The required sulfonyl oxime 1b was finally obtained in a 35%
Scheme 5. Radical additions to SEM sulfonyl oximes 15 and 17.
Table 2
Free-radical carbo-oximation of olefins with SEM sulfonyl oxime 1b
Entry Xanthate or
R1
Olefin R2
R3
Product Yielda
iodide 2
1
2
3
4
5
6
7
8
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
8 (X¼I)
PhO 3f
PhO 3b
PhO 3b
PhO 3c
PhO 3c
PhO 3d
PhO 3d
PhO 3g
PhO 3g
PhO 3k
PhO 3l
PhO 3m
PhO 3n
PhO 3o
PhO 3h
PhO 3p
CH2SiMe3
OPiv
OPiv
C6H13
C6H13
e(CH2)5e
e(CH2)5e
e(CH2)4e
e(CH2)4e
(CH2)2OTBDPS
(CH2)2OH
e(CH2)2NBoc(CH2)2e
e(CH2)2O(CH2)2e
OEt
H
H
H
H
H
19a
19b
19b
19c
19c
19d
19d
19e
19e
19f
d
82c
76b
73c
54b
69c
62b
77c
48b
69c
76c
0
9
10
11
12
13
14
15
16
17
18
19
20
Me
Me
19g
19h
d
61c
68c
0
H
Et
Et
Me
H
19i
19j
19k
19l
19m
19n
78c
80c
68c
52c
74c
64c
(CH2)2OBz
CH2SiMe3
C6H13
e(CH2)5e
OPiv
2d (X¼xanth.) Me 3f
2d (X¼xanth.) Me 3c
2d (X¼xanth.) Me 3d
2d (X¼xanth.) Me 3b
H
H
a
Isolated yield after chromatography over silica gel.
1 equiv of oxime 1b was used.
2 equiv of oxime 1b was used.
b
c
The reaction was next extended to a
-cyano xanthate 20,16 which
was shown to react with chloro-olefins 21aeb. This last result
demonstrates that the tin-mediated process is compatible with the
Scheme 4. Preparation of sulfonyl oxime SEM ethers 1b, 15, and 17.

10076
Y. Landais et al. / Tetrahedron 69 (2013) 10073e10080
presence of halogens, leading to the desired 3-component products
22aeb, albeit in moderate yields (Scheme 6).
3c, 3d, 3f, 3n
Scheme 6. Radical additions of a-cyano xanthates to SEM sulfonyl 1b.
We then studied the conversion of these SEM-oximes into the
corresponding aldehydes under various conditions. Fluoride sour-
ces (CsF, TBAT, TBAF),19,20 and acidic conditions were investigated to
trigger the conversion of oximes 19 into their corresponding al-
dehydes. While fluoride sources led to no reaction,22 efficient
deprotection was observed using TFA in CH2Cl2 (1:4 ratio) or
HFepyridine. At 0 ꢀC, the conversion was complete within two
hours and the crude yield of the aldehyde, after work-up, typically
reached 70e80%. Our attempt to purify aldehyde-esters 23aee
through chromatography led to some loss of material, but reason-
able isolated yields (ca. 40e60%) were however obtained (Scheme
7). In most cases, aldehydes were pure enough to be used in sub-
sequent transformations without further purification (vide infra).
3c, 3d, 3n
Scheme 7. Hydrolysis of 3-component products 19.
Scheme 8. Free-radical-3CR/oxime hydrolysis/Sakurai allylation or Mukaiyama aldol/
lactonization cascades.
We next evaluated the further transformation of 23aee, result-
ing overall from a formal carbo-formylation of olefins. The func-
tional groups embedded in 23aee, should provide, via simple
transformations, an access to functionalized cyclic substrates in
a limited number of operations. For instance, addition of a nucleo-
phile onto aldehydes 23 should provide an alcohol, which would
lactonize under suitable conditions, to afford 5,6-disubstituted
lactones. HosomieSakurai allylation23 and Mukaiyama aldol24
processes were first selected for this purpose using, respectively,
allyltrimethylsilane 3f and silyl enol ethers 25a (R3¼Ph) and 25b
(R3¼t-Bu) as nucleophiles (Scheme 8). Since the purification of the
aldehydes was inevitably hampered by some degradation on silica
gel, preliminary studies were designed as to carry out the following
sequence: free-radical 3-CR/oxime hydrolysis/Sakurai reaction in
a single pot, without purification of any intermediates. Such a pro-
tocol however did not produce the desired products in reasonable
yield. The free-radical process likely generates various by-products,
which interfere with the subsequent transformations. To address
this drawback, the 3-component products 19 were hydrolyzed us-
ing the method described above (using a 1:4 TFAeCH2Cl2 mixture)
and the resulting crude materials were purified through a short pad
of silica gel doped with KF,25 in order to remove tin residues. The
intermediate aldehydes were then isolated in reasonable overall
yields over two-steps (ca. 50%), and importantly, pure enough to be
used in subsequent Sakurai and Mukaiyama reactions. Hoso-
mieSakurai allylations conducted on these purified materials, in the
presence of a stoichiometric amount of TiCl4, produced the
expected lactones 24aed in good overall yield (50e60%) in three
steps from iodide 8. These overall yields indicate that the allylation
step proceeds very efficiently (>90%), albeit with poor diaster-
eocontrol (Scheme 8). This two-pot operation was next extended to
the Mukaiyama aldol, again using as originally described,24 TiCl4 to
mediate the reaction. Ketolactones 26aed were obtained with
slightly lower overall yields from 8 (30e40%), illustrating the
somewhat lower efficiency of the silyl enol ether 25aeb addition.
We next evaluated the behavior of these aldehydes with primary
amines in order to determine their level of performance in
Strecker26 and PicteteSpengler27 protocols. Treatmentof aldehydes,
issued from the multicomponent process between iodide 8, olefins 3
and sulfonyl oxime 1b, with benzylamine and then TMSCN28 pro-
vided the expected cyano-amides 27aec (Scheme 9). The latter are
versatile intermediates in particular for the generation of highly
reactive acyl-iminium species.29 Cyano-amides 27aec were isolated
in 40e60% overall yield in three steps/two-pot operation from 8.
With the objective of accessing more complex structural
motifs, our aldehydes were submitted to a PicteteSpengler-lac-
tamization cascade.30 The tricyclic framework obtained using
this strategy is present in many bioactive compounds including
natural alkaloids, such as protoemetinol 2831 and eburnamine
29.32 In practice, the aldehydes resulting from the free-radical 3-
component reaction/oxime ether hydrolysis were reacted with
tryptamine 30 in CH2Cl2 at room temperature, leading to the

Y. Landais et al. / Tetrahedron 69 (2013) 10073e10080
10077
isomer possessing the cis relative configuration as determined by
1H NMR. The PicteteSpengler-lactamization tandem process was
then extended to less reactive homoveratrylamine 32. The al-
dehydes issued from the free-radical 3CR were reacted with 32
following, as above, a one-pot protocol, without isolation of the
imine intermediate. The imine preformation required heating in
toluene at reflux for 2 h. TFA was then added to the resulting
imine and heating was then continued for a further 3 h. The
desired tricyclic substrates 33aee were isolated in 29e42%
overall yields over three steps from iodide 8. It is noteworthy
that 33a and 33b were obtained as single isomers. The cis-con-
figuration is likely the result of an iminium-enamine equilibrium
during the PicteteSpengler process, due to relatively harsh
acidic conditions. This contrasts with the stereocontrol obtained
for 31a issued from the same reaction with tryptamine, but
under milder conditions.
Scheme 9. Free-radical-3CR/oxime hydrolysis/Strecker/lactamization cascade.
corresponding imine intermediate, which did not required to be
isolated. In situ addition of TFA then triggered the Pictete-
Spengler-lactamization cascade,33 generating the tricyclic com-
pounds 31aee in reasonable overall yield over three steps
(Scheme 10). Diastereocontrol was again poor, with major
Finally, a combination between the free-radical carbo-oxima-
tion/oxime hydrolysis cascade and an intramolecular aldol re-
action was envisaged, which would offer a straightforward access
to
g
-substituted cyclohexenones.34 It was anticipated that hy-
drolysis under acidic conditions of SEM-protected oximes 19ken
bearing a methyl ketone (Table 2), followed by treatment of the
resulting keto-aldehyde with a base would produce the desired
cyclohexenones (Scheme 11). Unfortunately, all our efforts to
hydrolyze oximes 19ken using various conditions (TFAeCH2Cl2,
HCl, PTSA) met with failure. The presence of the methyl ketone in
these compounds likely interferes with the hydrolysis process.
Alternatively, the hydrolysis of the oxime benzyl ether in 3-
component adducts 4jek (Table 1), using an excess of formalde-
hyde was attempted.12,15 To our delight, under these conditions,
the corresponding aldehydes were formed in 50e60% isolated
yield. These were then treated either with base (KOH, MeOH) or
with acid conditions (conc. HCl in THF), affording in each case
reasonable yields of the desired g,g-substituted cyclohexenones
34aeb.
Scheme 11. Oxime hydrolysis/intramolecular aldolisation cascade.
3. Conclusion
In summary, a sequential carbo-formylation protocol involving
a 3-component radical carbo-oximationehydrolysis process was
developed. In order to avoid trans-oximation, which interferes with
the hydrolysis of the oxime ether, a new SEM-O-protected sulfonyl
oxime was prepared, and successfully used in the 3-component
radical carbo-oximation process. Its hydrolysis under mild condi-
tions allowed the carbo-oximation/oxime hydrolysis to be carried
out in a single pot. The resulting aldehydes were then elaborated
further, through a series of cascade reactions based on the distinct
and enhanced reactivity of the aldehyde over the ester functional
group. Sakurai allylation and Mukaiyama aldol reactions on the
aldehydes, immediately followed by spontaneous lactonization, led
to a series of lactones in good overall yield. In a similar fashion,
a Strecker reaction offered a straightforward access to cyano-
piperidinones, precursors of useful acyl-iminium reagents. A Pic-
teteSpengler-lactamization cascade on these aldehyde-esters with
tryptamine and homoveratrylamine was also devised, which de-
livered a number of piperidinones bearing polycyclic framework
Scheme 10. Free-radical-3CR/oxime hydrolysis/PicteteSpengler/lactamization cascade.

10078
Y. Landais et al. / Tetrahedron 69 (2013) 10073e10080
found for instance in eburnan alkaloids. All these cascades were
carried out using a three-step sequence from readily available
material, in a two-pot operation, thus limiting the number of pu-
rification steps.
dropwise to the heterogeneous reaction mixture. After total
consumption of the starting oxime, saturated aqueous solution
of NaHCO3 (10 mL) was carefully added and the mixture was
extracted with dichloromethane (3ꢁ10 mL). The organic phase
was dried over MgSO4, filtered, and concentrated in vacuo to
give a yellow oil, which was then subjected to silica gel chro-
matography (Petroleum ether/EtOAc 100:0/95:5) to yield 14
as a colorless oil (198 mg, 78%). Rf¼0.65 (Petroleum ether/
EtOAc 90:10). IR (neat, NaCl) nmax (cmꢂ1) 2953, 2879, 1568,
4. Experimental section
4.1. General procedure for the three-component carbo-oxi-
mation with sulfonyl oxime (1a) (Table 1). Three-component
adducts (4aet)
1486, 1247, 1107, 1004. 1H NMR (300 MHz, CDCl3)
d (ppm)
7.38e7.19 (m, 6H), 5.14 (s, 2H), 3.70 (t, J¼8.2 Hz, 2H), 0.91 (t,
To a solution of xanthate 2aee (0.21 mmol, 1.2 equiv), sulfonyl
oxime 1a (0.42 mmol, 2 equiv), (Bu3Sn)2 (1.5 equiv), and the alkene
3aej (4e5 equiv) in degassed benzene (1.8 mL, 0.1 M relative to 1a)
at 60 ꢀC was added DTBHN (di-tert-butylhyponitrite) (5 mol %)
every 90 min. After usually 2e4 additions, TLC indicated complete
consumption of the oxime component. Concentration in vacuo,
followed by purification by flash chromatography (silica gel with
10% KF (w/w), Petroleum ether/EtOAc) afforded oxime 4aet as
colorless oils.
J¼8.2 Hz, 2H), ꢂ0.03 (s, 9H). 13C NMR (75 MHz, CDCl3)
d (ppm)
146.4, 131.8, 131.1, 128.9, 128.1, 96.8, 66.6, 17.4, ꢂ1.8. HRMS
(ESI) calcd for
306.0954.
C
13H21NO2SSiNa [MþNaþ] 306.0963, found
4.2.3. Phenylsulfonylmethanal O-(2-(trimethylsilyl)ethoxy) methyl
oxime (1b). In a dry two-neck round-bottom flask equipped with
a condenser was dissolved oxime 14 (80 mg, 0.28 mmol) in dry
dichloromethane (5 mL). NaHCO3 (59 mg, 0.70 mmol), and m-
CPBA (195 mg, 1.12 mmol) were carefully added to the vigor-
ously stirred solution. The resulting heterogeneous mixture was
then heated to reflux overnight. The final white and heteroge-
neous mixture was partitioned between NaOH 10% and
dichloromethane. After the mixture had became clear, it was
poured into a funnel and the layers were separated. The aqueous
layer was washed with dichloromethane (3ꢁ10 mL). The com-
bined organic phases were dried over anhydrous MgSO4, filtered
and concentrated in vacuo. The crude residue was purified by
silica gel chromatography (Petroleum ether/EtOAc 95:5/90:10)
to afford 1b as a colorless oil (78 mg, 88%). Rf¼0.34 (Petroleum
ether/EtOAc 90:10). IR (neat, NaCl) nmax (cmꢂ1) 3614, 3060,
4.1.1. 4-Acetoxy-5-benzyloxyimino-4-methyl-pentanoic acid phenyl
ester (4a). Compound 4a was obtained according to the general
procedure described above from xanthate 2a (64 mg, 0.25 mmol,
1 equiv), sulfonyl oxime 1a (138 mg, 0.5 mmol, 2 equiv), iso-
propenyl acetate 3a (0.16 mL, 1 mmol, 4 equiv), (Bu3Sn)2 (0.19 mL,
0.38 mmol), and DTBHN (4 mg, 0.04 mmol, 10 mol %) added by
5 mol % portion every 1.5 h, in degassed benzene (1.5 mL). Con-
centration in vacuo, followed by purification by flash chromatog-
raphy (silica gel with 10% KF (w/w), Petroleum ether/EtOAc
95:5/90:10) afforded oxime 4a as a colorless oil (106 mg, 72%).
Rf¼0.22 (Petroleum ether/EtOAc 90:10). 1H NMR (300 MHz, CDCl3)
d
(ppm) 7.71 (s, 1H), 7.43e7.23 (m, 8H), 7.12e7.10 (m, 2H), 5.13 (s,
2H), 2.65 (t, J¼7.9 Hz, 2H), 2.45e2.25 (m, 2H), 2.06 (s, 3H), 1.67 (s,
3H). 13C NMR (75 MHz, CDCl3)
(ppm) 171.4, 169.8, 152.1, 150.7,
2962, 1699, 1446, 1306. 1H NMR (300 MHz, CDCl3)
d (ppm) 8.10
(s, 1H), 7.94e7.52 (m, 5H), 5.17 (s, 2H), 3.60 (t, J¼7.9 Hz, 2H), 0.85
d
(t, J¼7.9 Hz, 2H), ꢂ0.05 (s, 9H). 13C NMR (75 MHz, CDCl3)
137.4, 129.5, 128.4, 128.0, 125.9, 121.5, 79.9, 76.3, 33.8, 29.0, 22.8,
21.8. HRMS (LSIMS) calcd for C21H23NO5Na [MþNaþ] 392.1474,
found 392.1459.
d
(ppm) 149.7, 137.6, 134.4, 129.3, 128.1, 99.1, 67.3, 17.8, ꢂ1.5.
HRMS (ESI) calcd for C13H21NO4SSiNa [MþNaþ] 338.0865, found
338.0852.
4.2. Preparation of sulfonyl oxime (1b)
4.3. General procedure for the three-component carbo-oxi-
mation with sulfonyl oxime (1b) (Table 2). Three-component
adducts (19aen)
4.2.1. N-((2-(Trimethylsilyl)ethoxy)methoxy)formimidoyl
chloride
(13). In a dry two-neck round-bottom flask equipped with
a condenser was dissolved oxime 12 (37 mg, 0.21 mmol) in
anhydrous DMF (3 mL). NCS (42 mg, 0.31 mmol) was then added
and the resulting mixture was heated to 45 ꢀC. After total
consumption of the starting material, the yellow mixture was
partitioned between water (10 mL) and diethylether (10 mL)
and the layers were separated. The aqueous layer was extracted
with diethylether (3ꢁ10 mL). The combined organic phases
were dried over anhydrous MgSO4, filtered and concentrated in
vacuo. The crude residue was purified by silica gel chromatog-
raphy (Petroleum ether/EtOAc 100:0/95:05) to afford 13 as
a yellow oil (31 mg, 70%). Rf¼0.72 (Petroleum ether/EtOAc
75:25). IR (neat, NaCl) nmax (cmꢂ1) 3083, 2954, 2896, 1725, 1595,
In a dry two-neck round-bottom flask equipped with a con-
denser and a magnetic stirrer were successively added oxime 1b (1
or 2 equiv, See Table 2), iodoester 8 (1 equiv) and the desired alkene
partner (4e5 equiv) in benzene (0.4 M). Argon was then bubbled
directly into the flask for 30 min (Bu3Sn)2 (1.5 equiv) was then
injected and the flask was heated to 60 ꢀC. DTBHN was added after
5 min, then every 90 min if required (TLC). After total consumption
of the starting iodide, the resulting mixture was concentrated in
vacuo and purified by silica gel chromatography (Petroleum ether/
EtOAc) to afford the desired product.
1249. 1H NMR (200 MHz, CDCl3)
2H), 3.66 (t, J¼8.6 Hz, 2H), 0.89 (t, J¼8.6 Hz, 2H), ꢂ0.03 (s, 9H).
d
(ppm) 6.99 (s, 1H), 5.13 (s,
4.3.1. Phenyl 2,2-dimethyl-10-((trimethylsilyl)methyl)-5,7-dioxa-8-
aza-2-silatridec-8-en-13-oate (19a). Prepared according to general
procedure described above. Purification over silica gel (Petroleum
ether/EtOAc 98:2/90:10) afforded 19a as a colorless oil (82%).
13C NMR (63 MHz, CDCl3)
d
(ppm) 125.2, 97.2, 66.0, 17.5, ꢂ1.8.
HRMS (ESI) calcd for C7H16ClNO2SiNa [MþNaþ] 403.2060, found
403.2061.
Rf¼0.83 (Petroleum ether/EtOAc 75:25). IR (neat, NaCl) nmax (cmꢂ1
)
2976, 2957, 2855, 2711, 1732, 1690, 1513, 1278, 939. 1H NMR
4.2.2. 9,9-Dimethyl-1-phenyl-4,6-dioxa-1-thia-3-aza-9-siladec-2-
ene (14). In a flame-dried 25 mL two-neck flask equipped with
a magnetic stirrer, PhSH (0.16 mL, 1.56 mmol) was added to
a slurry mixture of NaH (37 mg, 1.56 mmol) in dry THF (5 mL)
at 0 ꢀC. After 1 h, oxime 13 (189 mg, 0.9 mmol) was added
(300 MHz, CDCl3)
d
(ppm) 7.36 (t, J¼8.1 Hz, 2H), 7.26e7.17 (m, 2H),
7.10e7.03 (m, 2H), 5.10 (AB syst., Jab¼8.2 Hz, 2H), 3.69 (m, 2H),
2.64e2.47 (m, 3H), 2.05e1.85 (m, 2H), 0.97 (t, J¼8.4 Hz, 2H), 0.78 (d,
J¼7.4 Hz, 2H), 0.12 (s, 9H), 0.09 (s, 9H). 13C NMR (75 MHz, CDCl3)
d
(ppm) 171.5, 155.7, 150.6, 129.2, 125.6, 121.4, 96.5, 65.8, 35.8, 31.8,

Y. Landais et al. / Tetrahedron 69 (2013) 10073e10080
10079
31.0, 21.1, 18.0, ꢂ0.9, ꢂ1.4. HRMS (ESI) calcd for C21H37NO4SiNa
[MþNaþ] 446.2158, found 446.2159.
90:10/70:30). Rf¼0.42 (Petroleum ether/EtOAc 75:25). IR (neat,
NaCl) nmax (cmꢂ1) 3453, 3041, 2912, 2859, 1742, 1622, 1459, 1201,
1043. 1H NMR (300 MHz, CDCl3)
d (ppm) 5.87e5.73 (m, 1H),
4.4. General procedure for the hydrolysis of the SEM-oxime.
Aldehyde (23aee)
5.19e5.06 (m, 2H), 4.06e3.94 (m, 1H), 2.58e2.25 (m, 4H), 1.89e1.65
(m, 3H), 0.73e0.51 (m, 2H), 0.04 (s, 9H). 13C NMR (75 MHz, CDCl3)
d
(ppm) 178.9, 178.7, 134.6, 117.8, 117.7, 67.5, 66.0, 40.0, 39.9, 39.1,
In a dry 10 mL round-bottom flask was dissolved the oxime 19
(0.1e0.2 mmol) in anhydrous dichloromethane (1.0 M). The color-
less solution was cooled to 0e5 ꢀC in an ice bath, then TFA (TFA/
CH2Cl2 1:4) was added dropwise under vigorous stirring. The ice-
bath was removed and the course of the reaction was monitored
by TLC. After total consumption of the starting oxime (1.5e2 h), the
slightly colored solution was directly concentrated under vacuum
to afford an oily residue, which was rapidly purified by flash
31.4, 31.3, 29.7, 28.4, 18.3, 16.4, ꢂ0.7, ꢂ0.8. HRMS (ESI) calcd for
C
12H22O2SiNa [MþNaþ] 249.1286, found 249.1290.
Acknowledgements
We gratefully acknowledge the ‘Agence Nationale de la
Recherche’ (ANR Blanc 07-3195-931), EU (IIF-Marie-Curie grant:
SEQ-MCR, Nꢀ251804), CNRS and MENRT for financial support.
ꢁ
chromatography over deactivated (Et3N) silica gel (60 A). The col-
umn was rapidly eluted with a mixture of Petroleum ether/EtOAc
(96:4/92:8) to isolate the expected aldehydes 23aee.
Supplementary data
Experimental procedures for compounds not described in the
experimental part can be found. Supplementary data related to this
article can be found at http://dx.doi.org/10.1016/j.tet.2013.09.051.
4.4.1. Phenyl 4-formyl-5-(trimethylsilyl)pentanoate (23a). Prepared
according to the general procedure described above from oxime
19a (162 mg, 0.38 mmol). Purification over silica gel (Petroleum
ether/EtOAc 98:2/90:10) afforded the desired compound as
a colorless oil (56 mg, 53%). Rf¼0.67 (Petroleum ether/EtOAc 90:10).
IR (neat, NaCl) nmax (cmꢂ1) 3423, 2953, 2715, 1759, 1723, 1594, 1493,
References and notes
1416, 1250, 1196, 841. 1H NMR (300 MHz, CDCl3)
d (ppm) 9.57 (d,
€
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Multicomponent Reactions In Multicomponent Radical Reactions; Zhu, J., Bien-
J¼2.6 Hz, 1H), 7.38 (t, J¼7.4 Hz, 2H), 7.23 (t, J¼7.4 Hz, 1H), 7.09e7.05
(m, 2H), 2.67e2.44 (m, 3H), 2.12e1.88 (m, 2H), 0.94 (dd, J¼7.1,
14.8 Hz, 1H), 0.63 (dd, J¼7.2, 14.9 Hz, 1H), 0.07 (s, 9H). 13C NMR
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In a dry two-neck round-bottom flask equipped with a con-
denser and a magnetic stirrer were successively added oxime 1b
(2 mmol), iodoester 8 (1 mmol) and the alkene 3 (5 mmol) in 1,2-
dichloroethane (2 mL). The reaction mass was degassed with ar-
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