Herein we report a condition-controlled divergent synthesis of spiro
indene-2,1’-isoindolinones and spiro isochroman-3,1’-isoindolinones
through cobalt-catalyzed formal [4 + 1] and [4 + 1 + 1]
spirocyclization of aromatic amides with
2-diazo-1H-indene-1,3(2H)-dione. When the reaction is
carried out under air in ethyl acetate, spiro indene-2,1’-isoindolinones
are formed through Co(II)-catalyzed C−H/N−H [4 + 1]
spirocyclization. When the reaction is run under O2 in
CH3CN, on the other hand, spiro
isochroman-3,1’-isoindolinones are generated through Baeyer-Villiger
oxidation of the in situ formed spiro indene-2,1’-isoindolinones with
O2 as a cheaper and environmental-friendly oxygen
source. In general, these protocols have advantages such as using
non-precious and earth-abundant metal catalyst, no extra additive, high
efficiency and regioselectivity. A gram-scale synthesis and the removal
of the directing group further highlight its utility.
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