Level 1 – Case 6
Stereospecific Substitution Reactions of Epoxy
Sulfides
Key point: Stereochemistry.
Neighboring group participation
O
SPh
R
H
H
Me 3 Al (3 equiv)
O
R
SPh
H
H
CH 2 Cl 2
CH 2 Cl 2
Me 3 Al (3 equiv)
R
SPh
OH
Me
R
SPh
OH
Me
-30
o C
-30
o C
Stereospecific Substitution Reactions of Epoxy Sulfides
The reaction of epoxy sulfides 1 and 2 with organoaluminium reagents is both regioselective and stereospecific. Thus, treatment of cis-1-(phenylthio)-2,3epoxyalkanes 1 with excess of Me 3 Al yielded after acid quenching, anti-hydroxy
sulfides 3, whereas trans-1-(phenylthio)-2,3-epoxyalkanes 2 under the same conditions, yielded syn-hydroxy sulfides 4. In both cases the yields of isolated products were greater than 95% (Scheme 6.1).
The reaction rates were very sensitive to a change in the solvent. Whereas dichloromethane was found to accelerate the process, the same reaction in hexane
gave very low yields of the open chain products together with and a large amount
of unreacted starting materials.
Explain the regio- and stereoselectivity of the reaction and justify the influence of
the solvent in the process.