Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters |
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| Authors: | Maria Camila Blanco?Jaimes Alexander Ahrens Daniel Pflästerer Dr Matthias Rudolph Prof?Dr A Stephen K Hashmi |
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| Affiliation: | 1. Organisch‐Chemisches Institut, Ruprecht‐Karls‐Universit?t Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany), Fax: (+49)?711‐685‐4205;2. Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia) |
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| Abstract: | Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. |
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| Keywords: | alkynes allenes furans gold lactones |
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