Miscellaneous Rearrangement Reactions

Question 1

This is an example of the Wolff Rearrangement from carbene chemistry
What is the mechansim and product

Answer 1

• Results in the formation of a ketene
• With the removal of dinitrogen as the driving force

Question 2

This is an example of the Curtius rearrangment from nitrene chemistry
What is the mechansim and product

Answer 2

• Results in the formation of a isocyanin
• With the removal of dinitrogen as the driving force

Question 3

Another type of rearrangement to electron-deficient carbon is called the Tiffeneau-Demjanov reaction
What is the mechanism and product of this reaction?

Answer 3

• Again the intermedite is primed to lose dinitrogen gas

Question 4

Another type of rearrangement to electron-deficient carbon is called the Tiffeneau-Demjanov reaction
What is the mechanism and product of this reaction?

Answer 4

• This method logistically may be a bit preferable as the handling of diazomethane is avoided

Question 5

What is the mechanism for the formation of an enolate from an ester

Answer 5

Question 6

What is the mechanism for the formation of an enolate from an ester with an nitrogen equivalent

Answer 6

• The central nitrogen is particuarly electron deficient
• Meaning the base is actually much better at removing a proton on the nitrogen eq - therefore use relatively weak bases

Question 7

• The Schmidt rearrangement is a similar reaction involving rearrangement to electro-deficient nitrogen
• It usually involves the reaction of a ketone with hydrazoic acid (HN₃) in the presence of another acid
• Note: the starting material has already been protonated for you

Answer 7

• Again the intermediate is driven by the removal of dinitrogen
• The reaction has inserted a NH group into one of the alkyl chains

Question 8

• The Schmidt rearrangement is a similar reaction involving rearrangement to electro-deficient nitrogen
  What is the product of this reaction?

Answer 8

Question 9

The analogous rearrangement to electron-deficient oxygen is known as the Baeyer-Villiger Oxidation and is very useful for converting ketones into esters
Peracids (peroxy-carboxylic acid) are the reagents used
What is the mechanism + product

Answer 9

• The peracid will reversibily protonate the ketone
• The cyclic arrangement of arrows allows one of the carbon substituents on the ketone from carbon to oxygen

Question 10

Draw out the structures of these common peracids:
Peracetic acid
Trifluoroperacetic acid
meta-chloroperbenzoic acid (m-CPBA)

Answer 10

Question 11

There is a choice the over which group migrates onto the oxygen within the Baeyer-Villiger Oxidation - Migratory aplitude
What order does this follow?

Answer 11

• The migratory aplitude of substituents in Baeyer-Villiger oxidation generally follows the order:
• Migration of methyl groups does not generally occur in Baeyer-Villiger reactions
• Sort of depends on which can stabilise being a carbocation more

Question 12

Why does this product of the Baeyer-Villiger oxidation occur?

Answer 12

• According to the migratory applititude series, the R₂CH will be more stable to holding a positive charge and therefore will migrate

Question 13

Why does this product of the Baeyer-Villiger oxidation occur?

Answer 13

According to the migratory applititude series, the Ar will be more stable to holding a positive charge and therefore will migrate

Question 14

Why does this product of the Baeyer-Villiger oxidation occur?

Answer 14

According to the migratory applititude series, the R₂CH will be more stable to holding a positive charge and therefore will migrate

Question 15

Why does this product of the Baeyer-Villiger oxidation occur?

Answer 15

• Though not affecting the stereochemistry is the path of least resistance
• According to the migratory applititude series, the R₂CH will be more stable to holding a positive charge and therefore will migrate

Question 16

Wagner-Meerwein shifts usually involve 1,2-shifts of hydrogen, alkyl,or aryl groups from one carbon to a neighbouring carbocation
What drives these reactions?

Answer 16

The driving force for these 1,2-shifts is the formation of more stable carbocations
i.e. the carbocation is more highly substitued OR the starting carbocation was extremely strained

Question 17

This is an example of a Wagner-Meerwein Shift
What is the product?

Answer 17

Question 18

This is an example of a Wagner-Meerwein Shift
What is the mechanism and product?

Answer 18

• The acid will protonate the OH group, creating a H₂O leaving group
• Forms a secondary carbocation
• Followed by a Wagner-Meerwein shift

Question 19

The pinacol rearrangement involes treatment of 1,2-diols with acid to convert them into carbonyl compounds

Answer 19

• After acificiation, the oxygen LP can come down and assist in breaking the C-Me bond needed for the migration to the carbocation
• LP is used to stabilise the positive charge