Asymmetric Cross [10+2] Cycloadditions of 2‐Alkylidene‐1‐indanones and Activated Alkenes under Phase‐Transfer Catalysis

Isobenzofulvene species are versatile synthons in organic chemistry, which have been employed in diverse challenging higher‐order cycloaddition reactions. Here, the first chemoselective and asymmetric cross [10+2] cycloaddition reaction between activated 2‐alkylidene‐1‐indanones and a variety of electron‐deficient alkenes has been developed, relying on the in situ generation of dearomative 1‐hydroxyl isobenzofulvene anion intermediates under the catalysis of a newly designed bulky cinchona‐derived phase‐transfer compound. An array of fused frameworks with multifunctionalities were generally furnished in excellent diastereo‐ and enantioselectivity, even at 1 mol % catalyst loadings. Higher‐order cycloaddition: The activated 2‐alkylidene‐1‐indanones can form dearomative 1‐hydroxyl isobenzofulvene anions under mild phase‐transfer conditions, and undergo highly chemoselective cross formal [10+2] cycloaddition reactions with a diversity of electron‐deficient alkenes. An array of polyhydrocyclopenta[a]indene frameworks with multiple functionalities were generally furnished in excellent diastereo‐ and enantioselectivity by employing a newly developed cinchona‐based ammonium salt, even at 1 mol % loadings.