A New Entry to the Stereoselective Introduction of an Ethynyl Group by a Radical Reaction: Synthesis of the Potential Antimetabolite 2′‐Deoxy‐2′‐C‐ethynyluridine

Atom-transfer 5-exo cyclization and subsequent elimination occur when ethynyldimethylsilyl ethers of iodohydrins are treated with Et3B followed by tetrabutylammonium fluoride (TBAF) to give the corresponding cis-configured α-hydroxy ethynyl compounds in high yield (see scheme). This is the first example of the use of a radical reaction to introduce an ethynyl group.