Gold-catalyzed cyclization of tert-butyl allenoate:: general synthesis of 2,4-functionalized butenolides

AuCl3 efficiently catalyzes cyclization of tert-butyl allenoates into gamma-butenolides. Advantage of directly using allenic ester precursor instead of corresponding acid is demonstrated in the synthesis of a variety of 2,4-disubstituted butenolides. A low catalyst loading and mild reaction condition makes this process an attractive alternative over conventional methods using strong Lewis acids. (c) 2005 Elsevier Ltd. All rights reserved.