New Cycloaddition Reactions of Anionically Activated Dipoles Daesung Lee, Department of Chemistry, University of Illinois at Chicago, IL 60607 New reactions of anionic dipoles: Based on the high reactivity of lithium trimethylsilyldiazomethane, various unprecedented transformations were developed including pyrazoline synthesis. The cycloadducts could undergo facile N–N bond cleavage under proteolytic conditions, giving free -amino ketones with a -cyanide substituent. .
OH
O
-78 ¡C, 20 min; SiO2
H N N
2
e
q
u
i
N N
72%
O
N2
NH2
2. N–N cleavage
CN O
O OMe
+
NH2
R H N N
2 equiv
-78 ¡C, 20 min to 25 °C; SiO2 R = H, 81% R = Cl, 93% R = OMe, 79%
.
1. Cycloaddition
92%
SiMe3
Li
Cl
O
v
SiMe3
1 equiv
O SiMe3
91% SiMe3
O
H O
Ph
CN
NH2 CN
94%
Ph
R
.
Application to natural product synthesis: The cycloaddition to form a pyrazoline followed by the N–N bond cleavage can be effectively employed for the synthesis of natural products containing -amino ketones and esters. O
O MeO
OTs
O
N2
N
MeO
Br
Li
Br OMe
Me3Si
MeO
N
MeO Br
Br
H N
NC TsOH
3 steps
Br
! =
Me
O N
H N
HO Br
SiMe3
Amathaspiramide D
OMe Br
OMe Br .
