7940
F. Liang et al. / Tetrahedron Letters 48 (2007) 7938–7941
O
S
O
S
Acknowledgements
O
S
R2NH2
OPh
R2HN
NHR2
Financial support of this research by National Natural
Sciences Foundation of China (20672019) and Science
Foundation for Young Teachers of Northeast Normal
University (20060313 and 20070305) is gratefully appre-
ciated. We would like to thank the referees for their
valuable suggestion on the proposed mechanism.
DMSO
120 oC
2h
1h
Scheme 2. Synthesis of thiomalonamides 2h.
a new and convenient route towards various functional-
ized thioamides of type 2. It should be noted that the
substrates with only one electron-withdrawing acetyl
or benzoyl group (1i and 1j) could not undergo the frag-
mentation reaction explored here, same as the substrates
without any acetyl groups (1k). In these cases, the sub-
strates were recovered quantitatively (Table 1, entries
20–22). In addition, the fragmentation reaction of six-
membered 2-acetylmethylene 1,3-dithiane with primary
amine under identical conditions was not observed.
Supplementary data
Supplementary data associated with this article can be
References and notes
On the basis of the experimental results, a plausible
mechanism for the formation of thioamides 2 is pro-
posed, as depicted in Scheme 3. Initially, a SNV (nucle-
ophilic vinylic substitution) type reaction11,12 leads to
the fragmentation of 1,3-dithiolane, giving rise to the
formation of the intermediate A. Driven by two strong
electron-withdrawing groups, an intramolecular elimi-
nation of thiirane takes place and intermediate B is
formed.13 Finally, thioamides 2 were produced through
a regioselective deacetylation (B!C!2).14 Such a type
of deacetylation is similar to that reported by Avery
and co-workers.14a
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O
O
O
O
OH
S
O
R1
R3NH2
R1
NHR3
R1
S
S
SH
S
NHR3
S
B
A
1a-g
(Thiirane)
R3NH2
H
O
R3HN
R3HN
O
O
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Am. Chem. Soc. 2005, 127, 4578–4579; (b) Dong, D.; Bi,
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O
R1
R1
NHR3
2a-g
NHR3
S
S
C
Scheme 3. Proposed mechanism for the formation of thioamides 2a–g.