Abstract
Abstract The nucleophilic substitution on a propargylic alcohol, ether or ester by a carbon or heteroatom nucleophile involving the generation of a carbocation by a strong Lewis acid, stabilization of the propargylic cation via the formation of hexacarbonyldicobalt alkyne complex, and final liberation of alkyne moiety by oxidation with cerium ammonium nitrate or N ‐methylmorpholine N ‐oxide is generally referred to as the Nicholas reaction. The Lewis acid BF 3 OEt 2 is the most commonly used acid for this reaction. All the favorable conditions and mechanism of the reaction have been discussed. It has been found that the application of an Evans's oxazoline enolate in coupling with a propargylic cation generates high stereoselectivity. This reaction has been used for the preparation of cyclic ethers and macrocycles.
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