Chemistry Reference
In-Depth Information
OMe
TBSO
MeO
CO
2
Me
TBSO
N
2
131
132
Rh
2
(
R
-DOSP)
4
2,2-DMB, 50°C
Rh
2
(
S
-DOSP)
4
2,2-DMB, 50°C
OMe
OMe
TBSO
TBSO
CO
2
Me
CO
2
Me
TBSO
TBSO
43% yield
91% ee
44% yield
92% ee
OMe
OMe
133
ent-
133
OMe
OMe
HO
HO
O
O
OH
HO
HO
OMe
54
OMe
134
(+)-Imperanene
(-)-Conidendrin
Scheme 4.34.
Synthetic applications of benzylic C- H insertion.
4.2.4.4. Allylic C-H Insertion
Double bonds can also act as activating groups due to
hyperconjugative interactions with adjacent C-H bonds. Furthermore, allylic stabiliza-
tion of the intermediate positive charge buildup in the insertion transition state is also
very favorable [3]. Mono- and
cis
-disubstituted double bonds are also prone to undergo
cyclopropanation reactions with metal carbenoids [85]. Muller and Tohill established
that donor/acceptor carbenoids derived from aryldiazoacetates undergo C- H insertion
preferably when competing cyclopropanation is possible [230]. For acceptor and accep-
tor/acceptor carbenoids, cyclopropanation is a much more favorable process. Conse-
quently, donor/acceptor carbenoids are excellent for this type of reactivity and have been
utilized extensively in allylic C-H activation chemistry [3,230].
