Abstract
Wilkinson’s catalyst [RhCl(PPh3)3] catalyzed
a cycloisomerization of allenynes which possess geminal
methyls on the allene terminus and an intramolecular ene-type reaction
proceeded to give various cross-conjugated trienes. Thermal Diels-Alder
reaction of the obtained triene was examined to give a bicyclic
compound in a high yield.
Key words
alkynes - allenes - catalysis - ene
reactions - rhodium
References
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A typical experimental procedure is
as follows (Table
[1]
, entry
9): Under an argon atmosphere, RhCl(PPh3)3 (3.7
mg, 4.0 µmol) was placed in a flask. A degassed toluene
solution (4 mL) of allenyne 1a (42.5 mg,
0.200 mmol) was added, then the mixture was stirred at 90 °C
(bath temperature) for 5 h. Solvent was removed under a reduced
pressure, then the resulting crude products were purified by thin
layer chromatography to give pure 2a (30.8
mg, 0.145 mmol, 73%). 2a: IR (neat)
3025, 2970, 2818, 1493, 1445 cm-1; 1H NMR
(300 MHz, CDCl3) δ = 1.96 (dd, J = 0.9 Hz, 1.5 Hz, 3 H), 4.30
(d, J = 3.2 Hz, 2 H), 4.58 (s,
2 H), 4.96-4.99 (m, 1 H), 5.08-5.11 (m, 1 H),
5.75 (t, J = 3.2 Hz, 1 H), 6.53
(s, 1 H), 7.12-7.35 (m, 5 H); 13C
NMR δ = 23.2, 65.2, 65.8, 115.2, 124.0, 126.1,
126.8, 128.1, 128.9, 131.9, 136.5, 140.5, 143.5; HRMS found m/z 212.1208,
calcd for C15H16O: 212.1201. The stereochemistry
of 2a was determined by the NOESY spectrum
in which NOEs between Ha and phenyl protons, and Hb and
Me protons were observed (Figure
[1]
).
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Using 0.5 mol% catalyst, 2a was obtained in 14% yield and 1a (58%) was recovered.
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carbonylative coupling of allenynes was reported:
Brummond KM.
Kerekes AD.
Wan H.
J. Org. Chem.
2002,
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5156 ; and references cited therein
