Accessing Phase-Transfer Catalysts and a Phosphoramidite Ligand via the Asymmetric Intramolecular Hydroamination Reaction

Within the last few years, our group has developed the intramolecular, asymmetric hydroamination (HA) reaction to a point where essentially enantiopure products can be obtained. The question then arose as to whether we can apply the reaction in useful ways beyond the synthesis of natural/pharmaceutically relevant products. In the present paper, we incorporate a select few HA products for the production of new chiral phase-transfer catalysts. These species are synthesized in one or two synthetic steps from new spirocyclic HA products and are applied in a classical substitution reaction, showing negligible enantioselectivity. In a second application, we introduce a novel phosphoramidite ligand, obtained by combining BINOL (1,1′-bi-2-naphthol) and an optically pure HA product with phosphorous trichloride. The representative ligand shows high enantioselectivity and activity in the rhodium-catalyzed conjugate addition reaction (Hayashi–Miyaura reaction).