A [3+2] - [4+2] - [3+2] cycloaddition sequence of isoquinolinium ylide

A unique [ 3 + 2] - [ 4 + 2] - [ 3 + 2] cycloaddition sequence of isoquinolinium ylide with aromatic aldehydes and indan-1,3-dione is investigated to afford polycyclic compounds with ten stereogenic centers in moderate to high yields. In this three-component reaction, the isoquinolinium salt has a triple function as a 1,3-dipole, an electron-rich dienophile and an electron-deficient diene. The observance of only one diastereomer verified the very high regio- and diastereo-selectivity,and the mechanistic rationale for the stereoselectivity is also discussed.