Insights into the gold-catalyzed propargyl ester rearrangement/tandem cyclization sequence: radical versus gold catalysis-Myers-Saito- versus Schmittel-type cyclization.
A detailed study of the gold-catalyzed tandem 1,3-carboxy migration/allene-enyne cycloisomerization was undertaken. It was found that after the initial allene formation the selectivity of the reaction is strongly influenced by the polarization of the remaining alkyne. Depending on the substitution pattern of the starting diynes, either a Schmittel- or a Myers-Saito-type cyclization was triggered. The 6-endo-dig Myers-Saito-type cyclization gave access to benzo[b]fluorenes, while the Schmittel pathway (5-exo-dig) delivered benzofulvenes as final products. In special cases a yet unknown pathway was opened by the ambiphilic nature of the allene moiety. In these cases completely different products were obtained by the nucleophilic attack of the alkyne moiety onto the allene that can also act as an electrophile. Mechanistic studies revealed that diradical pathways can be ruled out for this type of tandem cyclization reactions and it is shown that both steps of the reaction cascade are catalyzed by the gold complex.
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de.
Eva
E
Rettenmeier
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de.
Max M
MM
Hansmann
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de.
Alexander
A
Ahrens
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de.
Katharina
K
Rübenacker
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de.
Tapish
T
Saboo
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de.
Joy
J
Massholder
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de.
Christian
C
Meier
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de.
Matthias
M
Rudolph
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de.
Frank
F
Rominger
Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg (Germany) http://www.hashmi.de. hashmi@hashmi.de.|Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia). hashmi@hashmi.de.
A Stephen K
AS
Hashmi
alkynes; allenes; benzo[b]fluorenes; gold; propargylic carboxylates