Nitroxide Radicals: Properties, Synthesis and Applications - Stable Radicals: Fundamentals and Applied Aspects of Odd-Electron Compounds - page 204

NC

NC

N

140 ° C 3d or
MW 30 min.

N

O

+

NC

50 %

Scheme 5.47 Alkoxyamine addition to phenyl isonitrile

P(O)(OEt) 2

O O

O

N t- Bu 110 ° C, 12h

t- BuOH

+

t- Bu

O O

O O

60 %

SG 1

SG 1

ratio: 85 / 15

Scheme 5.48 Thermal homolysis of SG1-based alkoxyamine affording spiro-lactone with high stereoselectivity

However, TEMPO-based alkoxyamines present some drawbacks, such as high temperature of cleavage,
long reaction times, and hydrogen abstraction side reactions. To overcome these limitations, it has been
shown that steric effects from the nitroxide part play an important role on the reaction outcome and that
by using hindered nitroxides, such as SG1 (Scheme 5.48), such drawbacks can be overcome. 233,234

5.6.6.3 Reactions with organometallic compounds

The reactions of several classes of organometallic species with two equivalents of nitroxides have been
reported since the 1970s. 235

=

Li, Mg,
Zn, Cu, Sm, Ti, Zr) with TEMPO was demonstrated to proceed through the initial attack of TEMPO on
the metal atom to generate a carbon-centered radical that is subsequently trapped by the second equivalent
of TEMPO (Scheme 5.49).
TEMPO was also used as oxidant in transition metal-catalyzed reactions. Copper-catalyzed C-N and
C-O bond cross-couplings of secondary amines and phenols with arylboronic acid using TEMPO as oxidant
were successfully developed (Scheme 5.50). 236

The treatment of various organometallic compounds RM (with M

+ R M

+ R

N
O

N
O

+

M

R +

N
O

N
O

R

Scheme 5.49 Generation of radicals from organometallic species and subsequent trapping by TEMPO