A. Zhou, C. U. Pittman, Jr. / Tetrahedron Letters 45 (2004) 8899–8903
8903
CH3
N
S
Cl
C
O
C O
Et3N, THF
20 mins
CH3
N
S
+
S
O
O
84%
C
C
C
C
N
Cl
Cl
H3C
O
O
CH3
N
S
15
Scheme 4. The reaction of cyclic ketene-N,S-acetals with 1,3,5-benzenetricarbonyl trichloride.
chlorides to form ketene by loss of HCl would dominate,
leading to other side reactions.
associated with this article can be found, in the online
The reactions of N-methyl cyclic ketene-N,S-acetals 2
with diacid chlorides, which have no a-protons, proceed
readily in the same way to form the bis-a,b-unsaturated
ketones 14a–c in high yields (Table 5). Using diacid
chlorides with a-protons (succinyl chloride and glutaryl
dichloride) did not afford the analogous products. Com-
pound 14b was obtained as a pair of racemic diastereo-
mers, which have almost equivalent NMR chemical
shifts. Reacting 2 with 1,3,5-benzenetricarbonyl chloride
led to the tris-a,b-unsaturated ketone 15 in 84% isolated
yield; using a ratio of 2a/triacid chloride/Et3N = 3.6:1:4
(Scheme 4).
References and notes
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´
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Partial support of this work by the National Science
Foundation, Grant No EPS 012618 and by Mississippi
State University is acknowledged.
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Supplementary data
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The detailed synthetic and isolation procedures and the
full spectral identifications of all compounds are
provided in supplementary data. Supplementary data