No abstract

No abstract

Chiral spirooxindole is the core structure of a large number of natural and unnatural products with biological activities. However, the construction of trispirocyclic oxindoles remains challenging because of the difficulty in the assembly, the complex skeleton, and control of the stereoselectivities of the multiple quaternary stereocenters. Herein, we present the organic base/Au­(I)-catalyzed sequential asymmetric 1,2-addition/cascade hydroamination/HDA/deisobutene reactions for the elaboration of various trispirocyclic N,O-ketal tethered oxindoles and bisoxindoles in excellent optical purities (91–99% ee). Key to the success of this methodology is Au­(I)-catalyzed hetero-Diels–Alder reactions utilizing N-Boc-iminooxindoles as the heterodienes.

Polyketide oligomers containing the structure of tetracyclic isochroman comprise a large class of natural products with diverse activity. However, a general and stereoselective method towards the rapid construction of this structure remains challenging due to the inherent instability and complex stereochemistry of polyketide. By mimicking the biosynthetic pathway of this structurally diverse set of natural products, we herein develop an asymmetric hetero-Diels–Alder reaction of in-situ generated isochromene and ortho-quinonemethide. A broad range of tetracyclic isochroman frameworks are prepared in good yields and excellent stereoinduction (up to 95% ee) from readily available α-propargyl benzyl alcohols and 2-(hydroxylmethyl) phenols under mild conditions. This direct enantioselective cascade reaction is achieved by a Au(I)/chiral Sc(III) bimetallic catalytic system. Experimental studies indicate that the key hetero-Diels-Alder reaction involves a stepwise pathway, and the steric hindrance between in-situ generated isochromene and t-Bu group of Sc(III)/N,N’-dioxide complex is responsible for the enantioselectivity in the hetero-Diels–Alder reaction step.