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LETTER
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O
S
O
S
O
O
S
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OMe
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-MeOH
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Scheme 2 A proposed mechanism for the reaction of 3 with 2
In summary, two a,a-diacetyl cyclic ketene dithioacetals,
2a and 2b, have been developed as novel, non-thiolic,
odorless, efficient dithiol equivalents (1,3-propanedithiol
and 1,2-ethanedithiol) in the thioacetalization. In the pres-
ence of 2a and 2b, a wide range of carbonyl compounds,
aldehydes and ketones, have been converted into corre-
sponding dithioacetals, dithianes 4 and dithiolanes 5 in
high yields. Besides the generality in thioacetalization, 2a
and 2b exhibit significantly high chemoselectivity to pro-
tect an aldehyde in presence of a ketone. The novel thio-
acetalization is associated with simple procedure, mild
conditions and high yields, which leads it to the conve-
nient protocol for the syntheses of thioacetals and the pro-
tection of carbonyl compounds in laboratory and makes it
of great potential application in industry as well. Indeed,
the attempt to increase the reaction scale to prepare 50 g
of 2-phenyl-1,3-dithioane 4a from 2a and 3a was success-
ful. Further investigations of the application of the novel
reagents and the scope of the novel thioacetalization
reaction are in progress.
(9) (a) Choi, E. B.; Youn, I. K.; Pak, C. S. Synthesis 1988, 792.
(b) Mellor, J. M.; Schofield, S. R.; Korn, S. R. Tetrahedron
1997, 53, 17151.
(10) All dithioacetals 4, 5 and 9 prepared in the present work are
known compounds and were identified by 1H NMR, IR
spectroscopy and elemental analyses, the data for these
compounds are in good agreement with that in literatures.
Acknowledgment
Financial supports of this research by the NNSFC (20272008) and
the Key Project of Chinese Ministry of Education (03059) are
greatly acknowledged.
Synlett 2004, No. 6, 999–1002 © Thieme Stuttgart · New York