Electrophilic additions to alkenes can be stereospecific
المؤلف:
Jonathan Clayden , Nick Greeves , Stuart Warren
المصدر:
ORGANIC CHEMISTRY
الجزء والصفحة:
ص439
2025-06-02
498
Although they really belong with other nucleophilic substitution reactions, we included the last few examples of epoxide-opening reactions here because they have many things in common with the reactions of bromonium ions. Now we are going to make the anal-ogy work the other way by looking at the stereochemistry of the reactions of bromonium ions, and hence at the stereoselectivity of electrophilic additions to alkenes. We shall first remind you of an epoxide reaction, where you saw this.
The epoxide ring opening is stereospecific: it is an SN2 reaction and it goes with inversion. The epoxide starts on the top face of the ring and the amino group therefore ends up on the bottom face. In other words, the two groups end up anti or trans across the ring. You now know how to make this epoxide—you would use cyclopentene and m-CPBA, and in two steps you could ‘add’ an OH group and a Me2N group anti across the double bond.
Now we can move on to look at the stereochemistry of electrophilic addition to alkenes.
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