From ynamides to highly substituted benzo[b]furans: gold(I)-catalyzed 5-endo-dig-cyclization/rearrangement of alkylic oxonium intermediates.
A series of arylynamides with alkyloxy groups at the ortho position of the aryl group was prepared through a short alkylation/cross-coupling/amidation sequence. The gold-catalyzed conversion of these substrates combined both C-O and C-C formation steps, thus providing benzofurans with amine functionalities at the 2-position and alkyl groups at the 3-position. Cross-over experiments showed that the alkyl-migration step was an intermolecular process. X-ray crystal-structure analysis of two of the products supported our structural assignment. In some cases, the corresponding benzofurans without the alkyl group at the 3-position were obtained as side-products, which were formed through a competing protodeauration process.
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany), Fax: (+49) 711-685-4205.
Maria Camila
MC
Blanco Jaimes
Vanessa
V
Weingand
Frank
F
Rominger
A Stephen K
AS
Hashmi
cyclization; gold; heterocycles; rearrangement; ynamides