G. R€uedi, H.-J. Hansen / Tetrahedron Letters 45 (2004) 5143–5145
5145
tube furnace (1 m long), a condenser unit with a cooling
trap at the outlet side and a Kugelrohr oven as the
evaporation unit at the inlet side. A quartz tube (110 cm
long, 2.5 cm i.d.) which fitted into the furnace, was
connected to a trap (cooled with liquid N2) on one side
and to a bulb placed in the Kugelrohr oven on the other.
The starting material 2a (2.10 g, 9.4 mmol) was placed in
the bulb equipped with a capillary inlet device for the inert
flow gas (N2 flow 0.8–1.2 L/h) and a magnetic stirrer. After
evacuation ofthe apparatus with a high-vacuum oil pump
(2–4 Â 10ꢁ2 mbar) 2a was distilled directly through the
preheated reactor tube (620 °C reactor temperature; esti-
mated contact time <1 s). After all of the starting material
had been distilled (ca. 30 min), the apparatus was vented
and the frozen products were transferred to a bulb using
Et2O as solvent. The resulting solution was dried over
anhydrous MgSO4, filtered, and evaporated under reduced
pressure (>95% recovery). Purification by flash chroma-
tography on silica gel (hexane/AcOEt 60:1) afforded
recovered starting material 2a (1.32 g, 63%), 3a (0.48 g,
23%), and 4a (84 mg, 4%). Data of( E/Z)-3a: 1H NMR
(300 MHz, CDCl3): d 5.33–5.20 (m, 2H, H–C(5,6)), 2.61–
2.27 (m, 4H, CH2(2,15)), 2.05–1.95 (m, 4H, CH2(4,7)),
1.67–1.55 (m, 4H, CH2(3,14)), 1.38–1.23 (m, 12H); 13C
NMR (75 MHz, CDCl3): d 212.4, 211.7, 132.2, 131.4,
130.1, 129.2, 42.0, 41.5, 41.2, 40.8, 31.3, 30.0, 28.2, 27.1,
26.9, 26.8, 26.4, 26.2, 25.2, 24.7, 24.5, 24.0, 22.4, 22.3, 21.9;
Elemental analysis: calcd for C15H26O (222.37): C 81.02, H
11.78; found: C 80.92, H 11.75. Data of (E/Z)-4a: mp
procedure, no work-up, continuous process) and the low
price ofthe C-12 starting material. Our future efforts are
directed at enhancing the scope and selectivity ofthis
novel (n þ 3) ring expansion reaction.
Supplementary material: Experimental details and com-
plete spectral data ofthe compounds 2a–4a, and 6–8 are
given as Supplementary material.
Acknowledgement
This work was generously supported by the Swiss
National Science Foundation.
References and notes
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1
15 °C. H NMR (300 MHz, CDCl3): d 6.38–6.19 (m, 1H,
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H–C(14)), 6.10–5.91 (m, 1H, H–C(13)), 5.72–5.50 (m, 1H,
H–C(12)), 5.12–4.89 (m, 2H, CH2(15)), 2.41 (t, J ¼ 7:6 Hz,
2H, CH2(3)), 2.12 (s, 3H, H3C(1)), 2.10–1.98 (m, 2H,
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€
8. We thank Givaudan Research Ltd. Dubendorf(Switzer-
land) for expert olfactory evaluation.
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