2 3 accessing enantiopure endocyclic sulfoximines through 4 catalytic cycloisomerization of oxygenated propargyl-5 6 sulfinamides 7

Article abstract of DOI:10.1002/adsc.201801408

In this study, a novel strategy to access endocyclic sulfoximines in an enantiopure form is reported. The approach is based on a silver nitrate-catalyzed cyclo-isomerization reaction of oxygenated propargylic sulfinamides and provides efficiently 5-membered endocyclic sulfoximines (isothiazole 1-oxide). These new heterocyclic scaffolds can be isolated or directly converted into cyclic sulfinamides via Lewis acid-mediated sulfur deal-kylation reactions.

Full text of DOI:10.1002/adsc.201801408

Title: Accessing Enantiopure Endocyclic Sulfoximines Through
Catalytic Cycloisomerisation of Oxygenated Propargyl-
Sulfinamides
Authors: Pascale Cividino, Charlie Verrier, Christian Philouze,
Sébastien Carret, and Jean-François Poisson
This manuscript has been accepted after peer review and appears as an
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of the final Version of Record (VoR). This work is currently citable by
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201801408
Link to VoR: http://dx.doi.org/10.1002/adsc.201801408

10.1002/adsc.201801408
Advanced Synthesis & Catalysis
COMMUNICATION
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Accessing Enantiopure Endocyclic Sulfoximines Through
Catalytic Cycloisomerization of Oxygenated Propargyl-
Sulfinamides
Pascale Cividino,a Charlie Verrier,a Christian Philouze,a Sébastien Carreta and Jean-
François Poissona*
a
Université Grenoble Alpes, Département de Chimie Moléculaire, CNRS UMR 5250, 38000 Grenoble, France
Phone: (+33) 476635986; e-mail: jean-francois.poisson@univ-grenoble-alpes.fr
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Following our studies on the synthesis of
enantiopure oxygenated propargyl-sulfinamides,[12]
we envisioned that these unique substrates could
provide an easy access to unprecedented enantiopure
5-membered endocyclic sulfoximines, through a
simple cycloisomerization reaction, capitalizing on
the activation of the electron-rich oxygenated triple
Abstract. In this study, a novel strategy to access
endocyclic sulfoximines in an enantiopure form is reported.
The approach is based on a silver nitrate-catalyzed cyclo-
isomerization reaction of oxygenated propargylic
sulfinamides and provides efficiently 5-membered
endocyclic sulfoximines (isothiazole 1-oxide). These new
heterocyclic scaffolds can be isolated or directly converted
into cyclic sulfinamides via Lewis acid-mediated sulphur
dealkylation reactions.
bond by π-acidic transition metal catalysts.[13]
Me
Me
S
Keywords: Cyclization, Homogenous catalysis, Silver,
Sulfoximine, Sulfinamide, Acetylenic ethers
O
N
C
N
O
S
N
PPh2
F3C
N
Ph
iBu
Sulfoxalor (insecticide)
Ir Catalyzed
hydrogenation
Bolm
The preparation and functionalization of
sulfoximine derivatives have found an increasing
interest over the past decades.[1] These mono-aza
analogs of sulfones, presenting a sulfur-centered
chirality, have found successful applications in
organic synthesis as directing-groups,[2] chiral
auxiliaries[3] or chiral ligands in metal catalysis.[4]
They have also entered the realm of agrochemical
sciences with the insecticide sulfoxalor, the so far
sole marketed sulfoximine derivative, as well as in
the field of medicinal chemistry as bio-isosteres of
sulfones, carboxylic acids or amidines (Figure 1).[5]
In many cases, and especially for the use of
sulfoximine in catalysis, the control of the absolute
configuration of the sulfur center proved of major
importance. Despite this growing interest, only a few
methods are currently available for the synthesis of
enantiopure sulfoximines, relying mainly on
resolution of racemic mixtures,[6] the stereospecific
imidation of enantioenriched sulfoxides[7] and
oxidation of enantioenriched sulfimides,[8] or
imidative kinetic resolution of racemic sulfoxides.[9]
Owing to the interest of heterocyclic compounds in
medicinal chemistry, different strategies to access
cyclic sulfoximines have also been developed,
especially for the synthesis of 6-membered and
benzo-fused derivatives.[10] The preparation of 5-
membered cyclic sulfoximines remains less
explored[11] and their synthesis in enantiopure form is
limited to rather rare examples.[11c,e,f,h]
Dow chemical
O
Br
NH
O
O
S
Me
S
S
Me
P
N
N
Ph
Cox-2 inhibitor
Bolm
Rh Catalyzed
hydrogenation
Bolm
O
Me
MeO
MeO
S
N
Me
N
N
O
O
Me
N
S
N
N
S
O
Ph
Ph
Carboxypeptidase A inhibitor
O
Cu Catalyzed
Diels-Alder reactions
Tsay
Bolm
Me
Me
HN
O
S
Ph
S
N
N S
O
O
CYP24
Ph
Ph
hydroxylase
inhibitor
Posner
Pd Catalyzed
allylic substitution
Harmata
HO
OH
Figure 1. Examples of bioactive sulfoximines and
sulfoximine-based chiral ligands for asymetric catalysis
This study began with sulfinamide 3a, obtained in
a single step from the corresponding enantiopure tert-
1
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10.1002/adsc.201801408
Advanced Synthesis & Catalysis
butanesulfinylimine 1a by diastereoselective addition
of the in situ generated lithio acetylenic ether,
obtained by reaction of dichloroenol ether 2a with n-
butyllithium. A variety of -acid metals were tested
in dichloromethane for their ability to promote a
9
3b
3b
AgNO3 DCM
AgNO3 THF
Full conversion to methyl cinnamate was observed.
30
30
40-83[c]
92
10
[a]
[b]
[c]
Recovery of the starting sulfinamide.
reproducibility was observed.
Low
cyclisation.
Disappointingly,
a
very
fast
decomposition of the somewhat sensitive starting
sulfinamide acetylenic ether 3a was observed with
PtCl2, PdCl2, AuNTf2 or AgNO3 (Table 1, entries 1-
4); the presence of cinnamic derivatives in the crude
mixture seemed to point out a cleavage of the C-N
bond under the reaction conditions. Indeed,
performing the reaction in MeOH provided almost
quantitatively methyl cinnamate (Table 1, entry 5),
the result of the cleavage of the carbon-nitrogen bond
along with the loss of the asymmetric sulfur center
(Scheme 1, chart A). We then hypothesized that
introducing a less labile group on the oxygen atom
could prevent this side reaction pathway, and a
similar screening was conducted with sulfinamide 3b,
bearing a cyclohexyl ether instead of a tert-butyl
ether. This substrate proved more robust, as it could
be fully recovered in the presence of platinum (II)
dichloride (Table 1, entry 6). However, the use of
palladium (II) chloride or gold(I) triflimide did not
yield the expected heterocycle: a fast disappearance
of the sulfinamide was observed, along with the
generation of several unidentified byproducts (Table
1, entries 7 and 8). To our delight, when a catalytic
amount of silver(I) nitrate was employed, the
sulfoximine 4b could be obtained after 30 minutes of
reaction. However, we could not solve a problem of
poor reproducibility in this solvent with yields
varying from 40 to 83 % (Table 1, entry 9). Changing
the solvent from dichloromethane to anhydrous THF
was highly rewarding, with a very clean reproducible
The structure of ent-4b was unambiguously
ascertained by X-Ray diffraction showing an opposite
absolute configuration at the sulfur atom, due to
priority changes, as a result of the nucleophilic attack
on the acetylenic ether, sign of the direct interaction
of the sulfur lone pair with the activated triple bond
(Scheme 1). This X-ray was crucial to rule out a
putative formation of a six-membered ring, arising
from the nucleophilic attack of the oxygen atom of
the sulfinamide on the activated triple bond. A
mechanistic proposal to explain the results of metal
activation is depicted on Scheme 1. The silver ion
coordinates the electron-rich triple bond,[14]
enhancing its electrophilicity toward a nucleophilic
attack by the sulfur atom. A 5-endo dig cyclisation
occurs, thus generating intermediates of type I. In the
case of Ia, the tert-butyl group is labile enough to
promote
a Meyer-Schuster type rearrangement
providing a cinnamyl derivative of type II, that
subsequently degrades in DCM or generate methyl
cinnamate in MeOH, via nucleophilic displacement
of the sulfur-containing moiety (Scheme 1, case A).
In the case of Ib, its higher stability allows for a
protonation of the Csp2-silver bond (either by H-shift
or intermolecularly), along with the formation of the
N-S double bond of sulfoximine 4b (Scheme 1, case
B).
reaction, yielding 4b in 92
%
yield after
chromatography, as the sole product of the reaction
(Table 1, entry 10).
Table 1. Formation of sulfinamide 3, and optimisation of
the cycloisomerization reaction.
R1O
Cl
Cl
2a,b
n-BuLi
(2 eq.)
O
S
O
Cat
(10 mol%)
S
R1OCºCLi
S
N
HN
O
N
OR1
THF
-78 °C
Solvent
rt
Ph
Ph
Ph
OR1
4a,b
1a
R1 = t-Bu 3a
Cy 3b
Entry Substrate Cat.
Solvent Time Yield [%]
1
2
3
4
5
6
7
8
PtCl2
PdCl2
DCM
DCM
60
60
60
30
0
0
0
0
3a
3a
3a
3a
3a
3b
3b
3b
AuNTf2 DCM
AgNO3 DCM
AgNO3 MeOH 30
PtCl2
PdCl2
0[a]
0[b]
0
DCM
DCM
60
90
60
AuNTf2 DCM
0
2
This article is protected by copyright. All rights reserved.

10.1002/adsc.201801408
Advanced Synthesis & Catalysis
A:
product 4m could still be obtained, albeit in a much
O
tBu
O
S
O
lower yield (47%).
tBu
tBu
S
HN
O
S
H
HN
HN
O
S
AgNO3
(10 mol%)
O
S
HN
R2
t-Bu
Ph
O
Ph
Ph
N
OR1
OtBu
Ag
Ia
Ag+
THF
rt
II
3a
R2
OR1
4a-m
3a-g
B:
O
O
S
tBu
S
AgNO3 (10 mol%)
HN
N
O
O
O
OCy
S
S
N
S
THF
rt, 30 min
Ph
N
N
Ph
OCy
OCy
OCy
OCy
ent-4b
Ag+
ent-3b
O
tBu
H
H+ shift
S
Br
N
4b: 92%
4c: 67%
4d: 89%
OCy
Ib
Ph
Ag
O
O
O
S
N
S
N
S
N
OPMP
OPMP
OPMP
Me
4e: 71%
4f: 26%
4g: 58%
O
O
O
S
N
S
N
S
N
OPMP
OPMP
OPMP
O
F
Br
4h: 52%
4i: 85%
4j: 36%
Scheme 1: Mechanistic proposal for the degradation of 3a
(A) and for the formation of 4b (B) in the presence of
silver nitrate; X-ray structure of sulfoximine ent-4b
(obtained from the enantiomer of 3b)
O
S
O
O
S
N
S
N
N
OPMP
OCy
OCy
Ph
With optimal cyclisation conditions in hand, a
variety of oxygenated propargyl sulfinamides were
prepared[12] from both aromatic and aliphatic
4k: 0%
4l: 80%
4m: 47%
Scheme
2.
Scope
of
the
silver
catalyzed
sulfinylimines
bearing
cyclohexyl
and
p-
cycloisomerization of oxygenated propargyl-sulfinamides
methoxyphenyl acetylenic ethers, in order to study
the scope of the reaction. The results of the silver-
catalyzed cycloisomerization to 5-membered cyclic
sulfoximines are summarized in Scheme 2.
Modifications on the aromatic part were well
tolerated, as the naphthyl (4c) and a p-bromophenyl-
substituted (4d) derivatives were obtained with
similar efficiencies compared to the phenyl one. The
use of p-methoxyphenyl (PMP) acetylenic ether
proved successful with different aromatic or
heteroaromatic substituents: phenyl, o-tolyl, m-
bromophenyl and p-fluorophenyl were all effective
for the formation of the cyclic sulfoximines (4e,g,h,i),
whereas the naphthyl and furyl proved less
compatible, with lower yields of the products (4f,
26 % and 4j, 36 %). Starting with alkyl substituents
at the propargylic position proved somewhat
puzzling: the PMP derivative (4k) could not be
obtained whereas the cyclohexyl cyclic sulfoximine
4l could be secured in very high yield (80 %). With
the dihydrocinnamyl derivative 3m, the cyclized
3.
We next turned our attention on exploring the
reactivity of these novel heterocyclic scaffolds.
Attempts to react compound 4b with organometallic
species such as MeLi or MeMgBr did not lead to any
nucleophilic addition, but treatment by Lewis acids
such as boron trifluoride triggered the loss of the tert-
butyl group attached to the sulfur atom, yielding the
cyclic sulfinamide 5b in high yield (Scheme 3).[15]
We could ascertain the relative configuration of the
product as cis with X-ray structures of two products
(5d and 5f).
MeLi
or
MeMgBr
O
no reaction
S
N
O
OCy
S
BF3.OEt2
THF
HN
OCy
–80 °C to rt
4b
5a: 96%
3
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10.1002/adsc.201801408
Advanced Synthesis & Catalysis
filtered over celite, washed with dichloromethane and
concentrated under reduced pressure. The crude material
was purified by flash chromatography on silica gel to
afford pure 4b-l.
Scheme 3. Reactivity of the cyclic sulfoximine 4b
Interestingly, this derivative could also be obtained
in a one-pot procedure, by directly treating the
cycloisomerization reaction mixture at –80 °C by the
Lewis acid. In this way, different cyclic sulfinamides
were rapidly prepared from the corresponding
propargylic sulfinamides (Scheme 4), using aromatic
and aliphatic substituents at both the propargylic
center and the acetylenic ether part. The phenyl,
naphthyl and tert-butyl cyclohexyloxy-tethered cyclic
sulfinamides 5b-d were all obtained in fair yields
over the two steps one pot process. With a PMP-ether,
the cyclic sulfinamides 5e-h bearing aromatic
substituents at the initial propargylic position were
obtained in good yields over the two steps.
Typical procedure for the one-pot synthesis of cyclic
sulfinamides 5b-h:
To a solution of 3b-l (0.1 mmol) in dry THF (0.06 M) at
room temperature was added silver nitrate (10 mol%, 0.01
mmol). After disappearance of the starting material (30 to
60 min), the reaction was cooled to 78 °C and BF3.Et2O
(1.1 eq) was added dropwise. The reaction mixture was
then allowed to warm to room temperature over one hour.
The reaction was quenched with diluted NaHCO3 and
extracted with AcOEt. The organic layer was washed with
water, brine, dried (Na2SO4), filtered and concentrated
under reduce pressure. The purification of the crude
material by flash chromatography on silica gel yielded the
pure cyclic sulfinamides 5b-h.
O
CCDC-1579950, 1579951, and 1579952 contains the
supplementary crystallographic data for compounds ent-4b,
5d, and 5f in this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
O
O
AgNO3
(10 mol%)
S
BF3.OEt2
S
HN
R2
t-Bu
S
N
HN
OR1
1
OR
–90 °C to rt
THF
rt, 30 min
R2
R2
OR1
5a-g
3a-k
Acknowledgements
O
S
O
O
S
S
HN
HN
HN
We gratefully acknowledge the ANR (project Lycomet ANR-11-
JS-07-006-01), and Labex ARCANE (ANR-11-LABX-0003-01) for
financial support. We also thank support from ICMG FR 2607,
Grenoble, through which NMR and MS analyses have been
performed.
OCy
OCy
OCy
5c: 49%
5a: 65%
5b: 45%
O
O
S
O
S
References
S
HN
HN
HN
OPMP
R
OPMP
OPMP
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O
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5d: 71%
5g: 53%
Scheme 4. Scope of the one pot preparation of cyclic
sulfinamides
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heterocycles
incorporating
an
enantiopure
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4
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10.1002/adsc.201801408
Advanced Synthesis & Catalysis
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5
This article is protected by copyright. All rights reserved.

10.1002/adsc.201801408
Advanced Synthesis & Catalysis
COMMUNICATION
Accessing Enantiopure Endocyclic Sulfoximines
Through Catalytic Cycloisomerization of
Oxygenated Propargyl-Sulfinamides
Adv. Synth. Catal. Year, Volume, Page – Page
Pascale Cividino, Charlie Verrier, Christian
Philouze, Sébastien Carreta and Jean-François
Poisson*
6
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