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 (NaBH4) 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.