Fe(III)Halides as Effective Catalysts in Carbon-Carbon Bond Formation:Synthesis of l,5-Dihalo-1,4-dienes,alpha,beta-Unsaturated Ketones,and Cyclic Ethers

摘要

Iron(III)halides have proven to be excellent catalysts in the coupling of acetylenes and aldehydes.When terminal acetylenes were used the main products obtained were l,5-dihalo-1,4-dienes with CE,Z)-stereochemistry contaminated in some cases with(E)-alpha,beta-unsaturated ketones.The former carbonyl derivatives were the sole products isolated when nonterminal aromatic alkynes were used.When homopropargylic alcohols were used,a Prins-type cyclization occurred yielding 2-alkyl-4-halo-5,6-dihydro-2H-pyrans.In addition,anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization with homoallylic alcohols.Isolation of an intermediate acetal,calculations,and alkyne hydration studies provide substantiation of a proposed mechanism.