PhS
Br
Bu3SnH
MeO2C
CO2Me
AIBN
MeO2C
CO2Me
Map it out. Use the ester bound carbon as the starting point. We can see that there is a bond that
will be formed between C-5 and C-3
PhS
5 Br
5
3
4
2
3
4
MeO2C 1 CO2Me
2
MeO2C 1 CO2Me
Start the problem. Use AIBN to generate a tin radical (see radical handout 1), then form the bond using
a multiple bond addition reaction.
Br atom
extraction
multiple bond
addition
•SnBu3
PhS
PhS
PhS
Br
•
3
5
5
MeO2C
CO2Me
3
MeO2C
•
5
CO2Me
MeO2C
3
CO2Me
Map out the carbon atoms that you have not yet connected. It becomes apparent that C-6 needs to be connected
to C-5. Use a multiple bond addition to accomplish it.
multiple bond
addition
8
PhS
•
7
6
7
3
5
MeO2C
8
PhS
CO2Me
6
•
5
MeO2C
3
CO2Me
Finish the problem with a fragmentation reaction (the reverse of multiple bond addition). Then abstract a hydrogen
to regenerate Bu3Sn•
fragmentation
PhS
6
8
7
•
8
+
7
5
5
MeO2C
H
6
CO2Me
MeO2C
CO2Me
PhS•
SnBu3
PhSH
+
•SnBu3