From: Norwid-Rasmus Behrnd (behrndnr$##$yahoo.de)
Date: Fri Dec 05 2003 - 07:26:17 EST
Dear Hui Tong,
the transformation mentioned by you is called Corey-Fuchs-homologation. There is a
similarity between this reaction and the Wittig-Reaction.
In the first step, you transform your aldehyde in a dibromoalkene by use of
triphenylphosphine and tetrabromomethane (here, the new carbon-atom is introduced) in dry
dichloromethane at about 0 °C. Mix the phosphine and the bromide at about 0 °C in the
solvent and wait for at least 15 min to form the reagent, after add the aldehyde. A
yellow-reddish coloration is a good sign. You'll isolate the product first by adding
pentane which precipitates the formed triphenylphosphine oxide and filtering the mixture
through a pad of celite and after by chromatography.
The secound step is performed at lower temperatures (ca. - 78 °C): by adding two equiv.
of n-BuLi you form a terminal acetylide which may by trapped by an electrophile: in your
case adding water leads to terminal alkine. But by change of the electrophile, you may
synthesize internal alkines, too.
The original work : Corey, E. J.; Fuchs, P. L.Tetrahedron Lett. 1972, 36, 3769-3772.
An article, showing it's appliction within a total synthesis: "Studies Directed toward
the Total Synthesis of Discodermolide: Asymmetric Synthesis of the C1-C14 Fragment"
Arefolov A.; Anek, J. S.
Org. Let. 2002 Vol. 4, No. 14, 2397-2400.
Good luck,
Norwid
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