M. Pohmakotr et al. / Tetrahedron Letters 44 (2003) 7937–7940
Table 2. Preparation of compounds 6–9
7939
cis-4
Ar1
Ar2
% Yieldsa
6
7
8
9
cis-4a
cis-4b
cis-4c
cis-4e
cis-4f
cis-4i
cis-4j
cis-4k
Ph
Ph
Ph
Piperonyl
Piperonyl
4-MeOPh
4-MeOPh
4-MeOPh
Ph
6a, 85
6b, 95
6c, 90
6b, 93
6d, 94
6c, 96
6e, 95
6f, 93
7a, 85
7b, 86
7c, 88
8a, 83
8b, 89
8c, 82
9a, 70
9b, 82
9c, 75
Piperonyl
4-MeOPh
Ph
Piperonyl
Ph
b
b
b
–
–
–
7d, 86
8d, 80
9d, 74
b
b
b
–
–
–
Piperonyl
4-MeOPh
7e, 89
7f, 83
8e, 84
8f, 82
9e, 75
9f, 76
1
a Isolated yields. All compounds were fully characterized by IR, MS, 300 MHz H and 75 MHz 13C NMR spectra as well as by elemental analyses
or HRMS.
b The reactions were not performed.
yield. On the other hand, tetrahydrofurotetrahydro-
furans 9 were prepared in good overall yields by a
simple three-step synthesis starting from cis-dihydro-
furans 4. Catalytic hydrogenation (10% Pd on C) of
cis-4a in ethyl acetate at rt afforded a good yield (85%)
of the all-cis-7a as the sole isomer. Reduction of 7a
with LiAlH4 in THF at rt for 30 min gave 8a in 83%
yield after chromatography on silica gel. Treatment of
8a with p-toluenesulfonyl chloride in pyridine10 at rt
overnight furnished the expected tetrahydrofurotetra-
hydrofuran 9a in 70% yield. The 1H and 13C NMR data
of 9a were consistent with reported values.11 Thus, the
formation of 9a as the sole product and in good yield
confirmed the all-cis-stereochemistry in 7a. Under the
same reaction sequence and conditions, tetra-
hydrofurotetrahydrofurans 7b–f were prepared in good
yields from cis-2,3-dihydrofurans 4b, 4c, 4f, 4j and 4k,
respectively.
References
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Acknowledgements
We thank the Thailand Research Fund for financial
support (BRG/22/2544) to M.P. and the award of a
Senior Research Scholar to V.R. A.I. thanks the Min-
istry of University Affairs for a scholarship. Thanks are
also made to the Higher Education Development Pro-
ject: Postgraduate Education and Research Program in
Chemistry (PERCH) for support. We are grateful to
Professor Paul Knochel, LMU, Munich, Germany, for
the HRMS and CHN determination of some
compounds.