C–H Activation Induced by Oxidative Addition of N–O Bonds in Oxime Esters: Formation of Rhodacycles and Cycloaddition with Alkynes

The reaction of oxime
esters with a rhodium­(I) precursor to form
five-membered rhodacycles via N–O bond cleavage followed by
C–H bond activation has been investigated by isolating these
complexes. Kinetic studies on the formation of rhodacycles show that
the reversible oxidative addition of the N–O bond in the oxime
ester to RhCl­(PPh3)3 occurs at room temperature.
The E-isomer of the oxime ester was found to undergo
rhodacycle formation faster than the Z-isomer, which
suggests that the geometry of the oxime esters reflects the geometry
of intermediates during C–H activation. The rhodacycle reacted
with an alkyne to construct an isoquinoline ring in both stoichiometric
and catalytic conditions, despite its basic stability in air, in moisture,
and even during heating, which demonstrates the potential of the rhodacycle
as an intermediate for further catalytic transformation of oxime esters.