Synthesis of 2-Sulfonyl Indenes and Indanes.

In this paper, we developed facile and high-yield synthetic routes for the preparation of 2-sulfonyl indenes and indanes, including: (i) Amberlyst-15-promoted Knoevenagel reaction of β-ketosulfones and arylaldehydes in refluxing toluene; (ii) Grignard reagent (R'MgBr) or reducing reagent (NaBH) promoted regio- and/or stereocontrolled 1,4-addition or 1,4-/1,2-reduction of the resulting sulfonyl chalcones in THF or MeOH/THF at 25 °C; and then (iii) Amberlyst-15 mediated intramolecular Friedel-Crafts annulation of the corresponding β-ketosulfones or β-hydroxysulfones in toluene at reflux. This present method describes a highly efficient (3 + 2) annulation via the formation of two carbon-carbon (C-C) bonds. The DFT calculations were utilized to rationalize the regioselectivity of the addition reaction.