Cobalt-Catalyzed Switchable [4 + 1] and [4 + 1 + 1]
Spirocyclization of Aromatic Amides with
2-Diazo-1H-indene-1,3(2H)-dione: Access to Spiro
Indene-2,1’-isoindolinones and Spiro Isochro-man-3,1’-isoindolinones
Abstract
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.