Tetrahedron Letters
Methyltrioxorhenium/urea hydrogen peroxide catalyzed oxidation
of N-sulfinyl imines: A mild and highly efficient access to N-sulfonyl
aldimines, ketimines and
a-ketiminoesters
a,
Yu Tan a, Ru-Lin Ma a, Hua Lin b, , Xing-Wen Sun
⇑
⇑
a Department of Chemistry, Fudan University, 220 Handan Road, Shanghai 200433, PR China
b Biomedical Research Center of South China, College of Life Sciences, Fujian Normal University, Fuzhou 350117, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A mild and highly efficient access to N-sulfonyl imines through the oxidation of corresponding N-tert-
butylsulfinyl imines and N-p-tosyl-sulfinyl imines with UHP in the presence of catalytic amount MTO
was developed. Under mild reaction conditions, this highly selective reaction, provides a general and effi-
cient access to N-sulfonyl aldimines, ketimines and a-ketiminoesters in excellent yield. The unstable sul-
fonylimine intermediates can be afforded with high purity and ready for subsequent reaction without
Received 30 July 2020
Revised 29 September 2020
Accepted 18 October 2020
Available online xxxx
further purification. The application of this method was demonstrated by facile synthesis of quaternary
Keywords:
a-amino acids derivatives via allylation of obtained
a
-ketiminoesters.
Ó 2020 Elsevier Ltd. All rights reserved.
Methyltrioxorhenium
Urea hydrogen peroxide
N-Sulfinyl imines
N-Sulfonyl imines
Quaternary a-amino acids
N-Sulfonyl imines are versatile intermediates in a variety of
organic transformations [1], such as nucleophilic addition reac-
tions [2], hetero-Diels–Alder reactions [3], ene reactions [4], radical
reactions [5], as well as reductions [6], and other organic reactions
[7]. In light of the synthetic importance of sulfonylimines, a variety
of methods have been developed for their preparation [8]. The
direct condensation of aldehydes or ketones with sulfonyl amides
are most straightforward way to synthesize sulfonylimines. How-
ever, due to the weak nucleophilicity of sulfonamide, harsh condi-
tions are normally required and the scope are usually limited to
nonenolizable aldehydes. Ruano, J. L. G. and co-workers developed
a two-step process for obtaining N-sulfonylimines by reaction of
the corresponding aldehydes or ketones with sulfinamides and fol-
lowed by oxidation by dry m-CPBA [8]. The method features a
broad substrate scope, including aromatic and aliphatic carbonyl
compounds, even those containing enolizable protons. The tiny
flaw of this method is obviously, as a pure substance, m-CPBA
and efficient synthesis method of
derivatives remains elusive [10]. There are one report for the syn-
thesis of -sulfonyl ketimines esters by condensation methyl ben-
zoylformate and p-toluenesulfonamide catalyzed by TiCl4 in
CH2Cl2 under N2 to afford (Z)-Methyl 2-phenyl-2-(tosylimino)ac-
etate in 30% yield [10a,11].
During recent years, our research have been focusing on the
chemistry of N-tert-butanesulfinyl imines and enantioselective
arylation of N-sulfonyl imines for asymmetric synthesis of various
a-sulfonyl ketimines esters and
a
useful chiral amines [12]. N-Sulfonyl
substrates for the facile synthesis of plenty of
nucleophilic addition reactions have attracted our attention for a
long time. However, we found that the N-sulfonyl -iminoesters
are quite kinetically unstable and can be easily hydrolyzed to the
corresponding amines and -ketoesters during purification on sil-
ica gel. Therefore, a simple and efficient work-up or purification
a
-iminoesters as powerful
a-amino acids via
a
a
process for the synthesis of
desirable.
a-sulfonyl ketimines esters is a highly
can be detonated by shock or sparks.
as special N-sulfonyl imine derivatives, are useful synthetic inter-
mediates to provide -disubstituted -amino acids with a qua-
a-Sulfonyl ketimines esters,
Methyltrioxorhenium (MTO or CH3ReO3) has been widely used
as a catalyst in the formation of catalytically active peroxorhenium
species, with hydrogen peroxide or urea hydrogen peroxide com-
plex (UHP) as a stoichiometric oxidant [13]. During our studies in
a,a
a
ternary carbon center, which are important building blocks in
pharmaceutical research [9]. Despite their importance, the general
synthesis of N-sulfonyl
a-iminoesters, we noticed that organic
disulfides with either alkyl or aryl substituent can be oxidized to
thiosulfinates, thiosulfinate or sulfonic acids by hydrogen peroxide
in nearly quantitative yield under MTO catalysis [14]. Therefore,
⇑
Corresponding authors.
Sun).
0040-4039/Ó 2020 Elsevier Ltd. All rights reserved.
Please cite this article as: Y. Tan, Ru-Lin Ma, H. Lin et al., Methyltrioxorhenium/urea hydrogen peroxide catalyzed oxidation of N-sulfinyl imines: A mild
a
Tan, Yu
