Divergent Synthesis of Functionalized Spiroindanediones via CdI2/MgI2-Catalyzed Multiple Cyclocondensation Modes

Abstract Divergent synthesis enables rapid construction of structurally diverse compound libraries from the same universal substrates and is a current research hotspot. Here, the self-(3 + 2), (2 + 1), and (1 + 1 + 1) cyclocondensations of 2-arylidene-1,3-indanediones 1 were realized, respectively, by simply tuning the catalyst species and reaction temperature. The protocols enable access to various spiroindanediones 2, 4, and 5 in good to excellent yields (up to 91%). The products 2 can be further transformed into novel functionalized derivatives 3 by placing them in methanol/methanol-d4 (up to 89% yield, all >20:1 dr). Two core catalytic cyclocondensation pathways are proposed, including the CdI2-catalyzed (3 + 2) cyclocondensation initiated by O-Michael addition and the MgI2-promoted (2+1) cyclocondensation triggered by Michael addition.