Phosphine-Catalyzed (3 + 2) Annulation of δ-Hydroxyl Allenylic Alcohols with Pyrazolinone-Derived Ketimines

The phosphine-catalyzed (3 + 2) annulation reaction of δ-hydroxyl-substituted allenylic alcohols with pyrazolinone-derived ketimines has been developed, giving a variety of spiro dihydropyrrole-dihydropyrazolone derivatives in high yields with good diastereoselectivities. Various unsaturated pyrazolinone-derived ketimines and diverse allenylic alcohols worked well under mild reaction conditions, 31 examples were provided with up to 97% of yield and >20:1 diastereoselectivity. The scale-up reaction and further transformations of the product were successfully acheived, three derivation experiments showed the feasibility of the annulation product. These results revealed that the current reaction could be a useful tool for the synthesis of spiro dihydropyrrole-dihydropyrazolone derivatives. In addition, we also investigated the asymmetric version of this (3 + 2) annulation of allenylic alcohols with pyrazolinone-derived ketimines, up to 86% ee of chiral product was obtained with the use of chiral bifunctional phosphine catalyst.