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

Abstract

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.