[1,3]-Transfer of Chirality during the Nicholas Reaction in γ-Benzyloxy Propargylic Alcohols

✍ Scribed by David D. Díaz; Miguel A. Ramírez; Víctor S. Martín

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 331 KB
• Volume: 12
• Category: Article
• ISSN: 0947-6539
• DOI: 10.1002/chem.200501127

✦ Synopsis

Abstract

A highly regio‐ and stereoselective intramolecular [1,5]‐hydrogen‐transfer process is described. Treatment of γ‐benzyl‐protected Co~2~(CO)~6~‐α,γ‐acetylenic diols with BF~3~⋅OEt~2~ provides bis‐homopropargylic alcohols. The reaction occurs within seconds, tolerates a wide range of functionalities, and provides good yields. When the ether group is located at a stereochemically defined carbon atom, the rearrangement occurs with high stereoselectivity, transferring the chirality of the carbinol center to the newly created stereocenter. The cleavage of the benzyloxy group is totally regioselective when additional benzyl ethers are present. The scope and limitations of this novel process in densely substituted substrates are evaluated, and possible competitive reactions and/or stereochemical influences are also described. A mechanism based on a highly ordered chair‐like transition state substantiated by a theoretical study is also included.