Enantioselective Au(I)-Catalyzed Multicomponent Annulations via Tethered Counterion-Directed Catalysis

Gold­(I)
complexes of a chiral phosphoric acid-functionalized phosphine
of the CPA-Phos series enable the enantioselective multicomponent
reactions between aldehydes, hydroxylamines and cyclic yne-enones,
leading to 3,4-dihydro-1H-furo­[3,4-d]­[1,2]­oxazines. This represents a rare example of a highly enantioselective
multicomponent reaction in gold­(I) catalysis. The reactions proceed
at a low catalyst loading and provide high yields, total diastereoselectivity,
and enantiomeric excesses up to 99%. Silver-free conditions can be
applied. The method has a very broad scope as it applies to both aliphatic
and aromatic aldehydes and hydroxylamines, to a variety of cyclic
yne-enones, and to yne-enone-derived oximes. DFT calculations complement
this study to enlighten reactivity issues and mechanistic pathways.