Highly Regio-, Diastereo-, and Enantioselective 1,6- and 1,8-Additions of Azlactones to Di- and Trienyl N-Acylpyrroles
摘要:
A vinylog of Michael addition (1,6-addition) of azlactones to delta-substituted dienyl N-acylpyrroles been developed with virtually complete 1,6-diastereo-, and enantioselectivities by means of chiral P-spiro triaminoiminophosphorane as a catalyst. This system has been successfully extended to an unprecedented bis-vinylog of Michael addition (1,8 addition) of azlactones to zeta-substituted trienyl N-acylpyrroles with high levels of regio- and stereocontrol.
Unique site-selectivity control in asymmetric Michael addition of azlactone to alkenyl dienyl ketones enabled by P-spiro chiral iminophosphorane catalysis
and enantioselective 1,6-addition of azlactone to various alkenyl dienylketones has been achieved under P-spiro chiral triaminoiminophosphorane catalysis. This site-selectivity control relies on the distinct ability of the conjugate acids of iminophosphoranes, aminophosphonium ions, to precisely differentiate between the three electrophilic reaction sites of alkenyl dienylketones, which is further demonstrated
distinct catalysts. Cinchonidine‐derived thiourea catalyzes the 1,4‐addition of prochiral azlactone enolates to enynyl N‐acyl pyrazoles in a highly diastereo‐ and enantioselective manner to give stereochemically defined alkynes, while P‐spiro chiral triaminoiminophosphorane catalytically controls the stereoselective 1,6‐addition and the consecutive γ‐protonation of the vinylogous enolate intermediate