Enantioselective, Lewis Base-Catalyzed Sulfenocyclization of Polyenes
作者:Zhonglin Tao、Kevin A. Robb、Kuo Zhao、Scott E. Denmark
DOI:10.1021/jacs.8b01660
日期:2018.3.14
Homogeranylarenes and ortho-geranylphenols undergo polycyclization in good yield, diastereoselectivity, and enantioselectivity. The stereodetermining step is the generation of an enantiomericallyenrichedthiiraniumion from a terminal alkene and a sulfenylating agent in the presence of a chiral Lewis basic catalyst. The use of hexafluoroisopropyl alcohol as the solvent is crucial to obtain good yields
Brønsted acids (Chiral LBBAs) have been designed as new organocatalysts for biomimeticenantioselectivecyclization. A salt of a chiral phosphonous acid diester with FSO3H catalyzes the enantioselectivecyclization of 2-geranylphenols to give the desired trans-fused cyclized products with high diastereo- and enantioselectivities (up to 98:2 dr and 93% ee).
Chiral phosphite-urea bifunctional catalysts have been developed for the enantioselective bromocyclization of 2-geranylphenols with N-bromophthalimide (NBP) for the first time.
The first catalyticasymmetric bromonium ion-induced polyene cyclization has been achieved by using a chiral BINOL-derived thiophosphoramide catalyst and 1,3-dibromo-5,5-dimethylhydantoin as an electrophilic bromine source. Bromocyclization products are obtained in high yields, with good enantiomeric ratios and high diastereoselectivity, and are abundantly found as scaffolds in natural products.