価数の異なる金触媒の戦略的な利用：プロパルギルアルコールをテンプレートとする合成における多様性を指向した環化反応の開発

抄録

Cyclization reactions oriented toward synthetic diversity using propargylic alcohols have been developed by employing difference of valence of gold catalysts. Thus, strategic use of oxophilic (hard) gold(III) and π-philic (soft) gold(I) catalysts provides access to two types of cyclic ethers/piperidines from propargylic alcohols via intramolecular reactions. Treatments of propargylic alcohols with an oxophilic gold(III) catalyst (AuBr₃) result in cyclization to furnish cyclic ethers/piperidines/azepane bearing an acetylenic moiety, due to activation of the propargylic hydroxyl group by coordination of gold(III). On the other hand, similar treatments of propargylic alcohols with a π-philic gold(I) catalyst (Ph₃PAuNTf₂) induce Meyer-Schuster rearrangement, triggered by activation of the triple bond by coordination of gold(I), to afford α,β-unsaturated ketones, which undergo intramolecular oxa-/aza-Michael addition to give cyclic ethers/piperidines/azepanes having a carbonyl group. Expanding this strategy of intramolecular reactions to intermolecular reactions, synthesis of oxazoles/dihydropyrans from propargylic alcohols with amides/dicarbonyl compounds was achieved via gold(III)-catalyzed propargylic substitution and cycloisomerization. In addition, synthesis of 1,3-diarylindenes was achieved via dehydrative Friedel-Crafts reaction followed by Nazarov-type cyclization from propargylic alcohols with aromatic rings by gold(III)-catalyst.