Oxonium and thionium ion as intermediate Rezania

1. 1
Oxonium and Thionium ion as intermediate

2. oxonium ion:
In chemistry, the oxonium ion is any oxygen cation with three bonds.
The simplest oxonium ion is the hydronium ion H3O+.
Stable alkyloxonium salts exist; they are extensively used as alkylating agents. For
example, triethyloxonium tetrafluoroborate (Et3O+)(BF4
−) is a white crystalline solid.
2Oxonium

3. In acidic media, the oxonium functional group produced by protonating an alcohol
SN2:
3
The addition, follows Markovnikov’s rule
Hydroxy-alkoxy-addition
Oxonium
+

4. Oxonium ions are excellent alkylating agents, and ethers can be conveniently prepared by
treating them with alcohols or phenols
Alkyl halides can be alkylated by ethers or ketones to give oxonium salts
4Oxonium

5. Oxonium in advance synthesis
The term “carbenoid” refers to a metal-bound carbene, which results in a more stable species as
compared to a “free” carbene.
5Oxonium

6. 6
Common Metal Carbenoid Reactions
 Insertion reactions  Cyclopropanation
 Ylide generation
Oxonium

7. 7
One of the earliest examples of oxonium ylide generation from catalytically generated metal
carbenoids was provided by Nozaki et al. in 1966.
Oxonium

8. 8
oxonium ylides reactions
• [1,2]-shift reaction,
• [2,3]-sigmatropic rearrangement,
• insertion
• β-hydride elimination.
 [1,2]-Shift
Oxonium

9. 9
[1,2]-shift technique offers a new method for synthesising substituted carbocycles and
cyclic ethers.
Oxonium [1,2]-Shift

10. 10
[2,3]-Sigmatropic Rearrangement
1
23
1
2
Oxonium

11. 11Oxonium [2,3]-Sigmatropic Rearrangement

12. 12
Oxonium in the natural product (±)-vigulariol.
Oxonium,[2,3]-Sigmatropic Rearrangement

13. 13Oxonium,[2,3]-Sigmatropic Rearrangement

14. 14
Asymmetric Rearrangement
Oxonium[2,3]-Sigmatropic Rearrangement

15. 15Oxonium, [1,4]-Shift
[1,4]-Shift

16. 16
β-Hydride elimination
Oxonium hydride elimination

17. 17
Thionium:
Pummerer rearrangement:
in fact Thionium is synonym for pummerer rearrangement

18. 18
Mechanism
.
Common activators besides acetic anhydride are trifluoroacetic anhydride and
trifluoromethanesulfonic anhydride Common nucleophiles besides acetates are
arenes, alkenes, amides, and phenols.
Thionium:

19. 19
Even neutral nucleophiles can be used due to the highly electrophilic nature of the
sulfonium. for example, the electron-rich aromatic ring of veratrole.
Thionium:

20. 20Thionium:

21. 21
General Applications of the Pummerer Reaction
2.1 Pummerer Fragmentation Reactions
Thionium:

22. 22
These results suggest that a pKR+ value greater than 14.5 is necessary for fragmentation to
occur.
only the Pummerer
rearrangement
A , B give
fragmentation (4)
3C give a
mixture
Thionium:

23. 23
2.2. Vinylogous Pummerer Reactions
Thionium:

24. 24
2.3. additive Pummerer Reactions
Thionium:

25. 25
2.4. Interrupted Pummerer Reactions
Successful reaction requires the absence of an
amidic hydrogen;
Thionium:

26. 26
Pummerer Reaction Using an Alternative Method of Thionium Ion Formation
The Connective Pummerer Reaction
Thionium:

27. 27
Asymmetric Pummerer Reactions
Thionium:

28. 28
The Pummerer Reaction in Natural Product Synthesis
Synthesis of Monomorine
Thionium:

29. THANK YOY