Communications
Keywords: cyclization · palladium · spiro compounds ·
.
tandem reactions
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Scheme 4. The proposed reaction pathway (see text for details).
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In conclusion, we have developed a novel palladium-
catalyzed intermolecular tandem reaction for the synthesis of
tetracyclic compounds with sequential high regioselectivity
and with reaction conditions compatible with sequential
transformations of various functional groups of easily acces-
sible substrates. It is noteworthy that the mechanism was
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Experimental Section
General procedure (Table 1, entry 1): Cs2CO3 (130.4 mg, 0.40 mmol)
was added to a solution of 3-(2-(2,2-di(ethoxycarbonyl)ethyl)phe-
nyl)prop-2-ynyl ethyl carbonate 1a (75.2 mg, 0.20 mmol) in DMF
(2.0 mL). The mixture was stirred for 5 min and [Pd(PPh3)4] (11.5 mg,
0.01 mmol, 5 mol%), and 2-iodophenol 2a (66.0 mg, 0.30 mmol) were
added. The resulting mixture was then heated under an argon
atmosphere at 1008C. When the reaction was considered complete as
determined by thin-layer chromatography, the reaction mixture was
allowed to cool to room temperature and quenched with a saturated
aqueous solution of ammonium chloride, and the mixture was
extracted with ethyl acetate. The combined organic extracts were
washed with water and saturated brine. The organic layers were dried
over Na2SO4 and filtered. Solvents were evaporated under reduced
pressure. The residue was purified by chromatography on silica gel to
afford 3a 51.4 mg (68%) as an oil.
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Received: May 21, 2007
Published online: August 7, 2007
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2007, 46, 7068 –7071