Gold-Catalyzed Cyclization of Nonterminal Propargylic Amides to Substituted Alkylideneoxazolines and -oxazines

作者：Hashmi A Stephen K^*; Schuster Andreas M; Schmuck Martin; Rominger Frank

来源：European Journal of Organic Chemistry, 2011, 2011(24): 4595-4602.

DOI：10.1002/ejoc.201100342

• Alder-ene reaction
• Cyclization
• Alkynes
• Amides
• Gold
• Oxazoles
• Oxazines

The substrate scope of the gold-catalyzed cyclization of nonterminal propargylic amides to oxazolines and oxazines was investigated. Sixteen alkyl-substituted and 35 aryl-substited substrates were prepared by a very variable route from tri-methylsilyl-(TMS-)protected, nonterminal propargylamines. Steric and electronic influences of the substituents on product selectivity were studied. A chloromethyl substituent on the alkyne shows an efficient 1,4-elimination to deliver vinyl-oxazoles. A second alkynyl group, tethered to the alkyl group at the alkyne, in some cases led to a gold catalysis/Alderene domino reaction. With Barluenga's reagent the iodoalkylideneoxazoline can be formed in excellent yield. In contrast to the palladium-catalyzed protocols, the gold-catalyzed conditions for the cyclization of nonterminal propargylic amides are much milder, thus, for example, no special precautions are needed to prevent isomerization of the oxazolines to the aromatic oxazoles.

• 出版日期2011-8