123.202 alkenes

1. LEC TURE EIGHT
alkenes II ©DaveKav@flickr

2. PREVIOUSLY...
hydrogenation
H H
X
H X
H
started addition (hydration etc)

3. regiochemistry
©Stéfan@flickr

4. Markovnikov Addition
get richer
the rich
©velo_city@flickr

5. Markovnikov Addition
H➀ H➀
H
H ➂ H
➁ H
H H
get richer
the rich

6. ©tintin44@flickr

7. cation
stability
H H
X
H X
H
primary cation
least
stable

8. oxymercuration
i. Hg(OAc)2,
H2O
ii. NaBH4
HO
H
Markovnikov
Addition

9. mechanism OAc
Hg
AcO OAc OAc
Hg
HgOAc
OAc
step 1

10. OAc
H HgOAc
H Hg SN2-like O
O H
H
anti OAc
HgOAc
HO
mechanism
step 2

11. HgOAc H
HO NaBH4 HO
mechanism
step 3

12. do NOTT
NO
believe everything
you read on...

13. hydroboration
BH3 H
BH2
addition
of
BH3

14. simplification
gross

15. BH3 is
actually
H H H
B B
H H H

16. or
R R
X
H B
Hmplex
co
H of
Lewis Base

17. ©the_monk@flickr

18. group 13
δ– δ+ H
H B
H

19. organoboranes
are unstable
H
BH2

20. ©the_monk@flickr

21. group 13
δ– δ+ H
H B
H

22. typical reaction
i. BH3
ii. H2O2/
NaOH H
OH
anti Markovnikov
Addition

23. ©quinn.anya@flickr

24. group 13
δ– δ+ H
H B
H

25. δ+
> δ–
alkyl groups
are
electron donating

26. step 1
hydroboration
δ–
H δ+
H
δ+
BH2
BH2
δ–
match
polarities

27. step 2
oxidation
H2O2
H NaOH H
BH2 OH
1,2-shift
retention

28. hydroboration
δ– δ+
H BH2 H BH2
δ+ δ–
H
H2O2
NaOH
H OH
syn
Addition
H

29. hydroboration
H BH2 H BH2
H
H2O2
NaOH
H OH
syn
Addition
H

30. stereospecific
syn Addition H OH
i. BH3
ii. H2O2
NaOH
H OH
concerted
bond formation

31. O
anti-TB OH
H
O
H
colombiasin A
©Artiii@flickr

32. OMe
OMe
OMe
OMe i. BH3•THF;
aq. NaOH, H2O2
ii. PCC
TBSO
TBSO H
H (79% overall)
OMe
OMe
O
example