Tetrahydrofuran synthesis using gold

Other nucleophiles that have been used in this context are acetylides (alkynes). The addition of those to iminium cations generated in situ from aldehydes and secondary amines accomplishes a gold(III)-catalyzed three-component coupling for the synthesis of propargylamines, as can be observed in equation (124). The reactions are performed in water or in tetrahydrofuran (THF) when supported catalysts are employed.Chiral prolinol derivatives as... 

Extension of the method to the synthesis of enantiomerically enriched tetrahydrofurans or tetrahydropyrans was possible by using chiral phosphine ligands on the gold catalyst. In the presence of chiral gold pre-catalyst [Au2 (.S)-3,5-r-Bu-4-MeO-MeOBIPHEP Cl2] and AgOTs, prochiral allenes afforded the desired heterocycles with high enantioselectivity (Scheme 4-101). 

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