Enantioselective Cyclizations of Silyloxyenynes Catalyzed by Cationic Metal Phosphine Complexes

The discovery of complementary methods for enantioselective
transition metal-catalyzed
cyclization with silyloxyenynes has been accomplished using chiral
phosphine ligands. Under palladium catalysis, 1,6-silyloxyenynes bearing
a terminal alkyne led to the desired five-membered ring with high
enantioselectivities (up to 91% ee). As for reactions under cationic
gold catalysis, 1,6- and 1,5-silyloxyenynes bearing an internal alkyne
furnished the chiral cyclopentane derivatives with excellent enantiomeric
excess (up to 94% ee). Modification of the substrate by incorporating
an α,β-unsaturation led to the discovery of a tandem cyclization.
Remarkably, using silyloxy-1,3-dien-7-ynes under gold catalysis conditions
provided the bicyclic derivatives with excellent diastereo- and enantioselectivities
(up to >20:1 dr and 99% ee).