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Unformatted text preview: 2 NaI + 2 H2O • mechanistically: a series of SN2 reactions!
R—S—H + –OH R—S– + H2O R—S– + I—I R—S—I + –I R—S– + R—S—I R—S—S—R + –I 10-60! Disulﬁdes!
When thiols and disulﬁdes are mixed, an
equilibrium among them is rapidly established,
governed by the leaving group capacity to leave:! SH + SH + SS SS SS SS + + SH SH 10-61! Designing Multistep Syntheses!
1. !Review the functional groups and carbon skeleton of the target.! 2. !Review the functional groups and carbon skeleton of the
starting materials and evaluate how their skeletons might ﬁt together
to make the target compound.! 3. !Use the retrosynthetic approach to compare methods for
assembling the carbon skeleton of the target compound to give the
proper connectivity and functional group regiochemistry.! 4. !Bias your selection of retrosynthetic pathways towards the
• add less reactive groups earlier in a synthesis and more reactive groups later; and!
• utilize the lowest number of overall synthetic steps.! 5. !Summarize the complete synthesis in the forward direction,
including all steps and all reagents, and check for errors/omissions.!
10-62! Example of Retrosynthetic Design!
How could the following cyclic ether be prepared from the
starting material shown?!
?? Br O Retrosynthetic analysis:! OH Br Br O
indicates that you
are working the
problem backwards One possible solution:!
Br 1) Hg(OAc)2, H2O
2) NaBH4 OH Na0 Br
Et2O O 10-63! Synthesis Problem!
How would you synthesize!
OH OH HO OH ! ! ! !from ! ! ! !?!
10-64! Retrosynthesis & Forward Synthesis!
HO OH O O OH O O Forward Synthesis:!
O O 1) O3 OH OH NaBH4 2) Me2S
O O HO OH 10-65! Design Multistep Syntheses for the Following Transformations!
O O OH Br OH
+ 10-66! Multistep Synthesis Examples!
How would you synthesize the target compound
from the given starting materials?!
CD3I + CH3I + CH3 OH + CD3 Williamson ether synthesis!
O CH3 Grignard reaction with ketone!
CD3 Grignard reaction with epoxide! 10-67!...
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