Organic Letters
Letter
a
Table 1. Optimization of the Reaction Conditions
products 3a−h in yields ranging from 53 to 91%. Although the
number of examples was limited, the presence of electron-
withdrawing substituents on the arenes appeared to have a slight
negative effect on the yields of the corresponding products [for
example, 82% of 3b (with 4-Me) versus 53% of 3e (with 4-CN)].
Steric crowding played a minor role, as revealed by the yields of
entry
catalyst
additive
solvent
yield (%)
3
f−h (72−84%). Noteworthy, for 3-methoxy-substituted 3h,
1
2
3
4
5
6
7
8
9
Rh(cod)Cl2
CuCl2
DCE
DCE
DCE
DCE
acetone
THF
toluene
DCM
DCE
DCE
DCE
DCE
DCE
DCE
DCE
11
only one regioisomer was observed, presumably due to a higher
reactivity of the less congested C−H bond site. Sulfoximines
with S-alkyl groups other than methyl also reacted well, as shown
in the results for S-alkyl-S-phenylsulfoximines 3i−m with yields
of 58−85%. In light of the high reactivity of S-chloromethyl- and
trace
trace
75
60
45
38
65
11
trace
91
PdCl2
[Cp*RhCl2]
[Cp*RhCl2]
[Cp*RhCl2]
[Cp*RhCl2]
[Cp*RhCl2]
[Cp*RhCl2]
[Cp*RhCl2]
2
2
2
2
2
2
2
15
S-benzyl-substituted sulfoximines, the data for 3i and 3k with
yields of 83 and 85%, respectively, are remarkable. Branching at
the S-alkyl substituent as in 3m bearing an S-isopropyl group
seemed to hamper the product formation (58% yield). The
applicability of S,S-diarylsulfoximines was shown in conversions
of 2a with 1n and 1p, which afforded 3n and 3p/3p′ in yields of
60 and 67%, respectively. The latter product was obtained as a
1:1 mixture of positional isomers. The attempt to react
dibenzothiophene sulfoximine (1o) under the optimized
conditions failed, and thus, 3o remained inaccessible. This
result was in line with previous observations which revealed a
NaOAc
1
1
1
1
1
1
0
1
2
3
4
5
NaHCO3
[Cp*RhCl2]
2
PivOH
[Cp*RhCl2]
2
CH COOH
3
13
80
88
87
[Cp*RhCl2]
[Cp*RhCl2]
2
1-AdCOOH
PivOH
PivOH
b
2
c
[Cp*RhCl2]2
a
Reaction conditions: 1a (0.10 mmol), 2a (0.15 mmol), catalyst (3
mol %), AgSbF (12 mol %), and additive (0.10 mmol) in the given
solvent (1 mL) at 100 °C for 10 h. Under argon atmosphere. Use of
16
6
very particular reaction behavior of compounds of this type.
b
c
Using S-methyl-S-phenylsulfoximine (1a) as the reaction
partner, the applicability of other dioxazolones 2 was tested.
Again, the catalyses proceeded smoothly, providing the expected
products 3q−t in yields ranging from 72% (for 3r) to 86% (for
2
.0 equiv of 2a (0.20 mmol).
Under the optimized conditions (Table 1, entry 11), the
3
q).
On a 1 mmol scale, the reaction between 1a and 2a led to 3a in
substrate scope was evaluated. As shown in Scheme 2, the
process was very general, allowing a wide range of both
sulfoximines 1 and dioxazolones 2 to be converted with high
structural diversity. In the series of S-aryl-S-methylsulfoximines,
reactions with 2a proceeded well, providing the corresponding
8
1% yield.
To further understand the reaction pathway, several control
experiments were performed. Under standard conditions with
a and 2a as substrates, the presence of 2 equiv of TEMPO or
1
BHT decreased in yield of 3a from 91% (Table 1, entry 11) to 61
and 65%, respectively, indicating that the reaction did not
involve free radicals being trappable by such typical radical
scavengers (Scheme 3, reaction a). Reacting benzoyl-substituted
Scheme 2. Substrate Scope with Respect to Sulfoximines and
1
,4,2-Dioxazol-5-ones (0.1 mmol Scale)
Scheme 3. Control Experiments
sulfoximine 4a with 2a gave amidated product 5a in 71% yield
(
Scheme 3, reaction b) showing that N-substituted sulfoximines
could also be applied in this C−H bond activation process with
a and that, in the original system, the free NH group of the
2
sulfoximine was essential for the benzothiadiazine-1-oxide
formation.
10,17
Based on these results and previous reports,
a plausible
catalytic cycle is proposed in Scheme 4. Cationic rhodium
complex I generated by anion exchange of [Cp*RhCl ] with
2
2
B
Org. Lett. XXXX, XXX, XXX−XXX
Bolm, Carsten
