exam 4 helpful reagents

Question 1

[H3O+], Br2

Answer 1

α-Bromination
These reagents can be used to install a bromine atom at the T position of a ketone (or aldehyde). Subsequent treatment of the resulting α-bromoketone with pyridine gives an α,β-unsaturated ketone. This two-step process can be used to introduce α,β-unsaturation into a ketone or aldehyde.

Question 2

1. Br2, PBr3
2. H2O

Answer 2

Hell-Volhard-Zelinsky reaction
These reagents can be used to install a bromine atom at the α position of a carboxylic acid.

Question 3

1.NaOH, Br2
2.H3O+

Answer 3

Haloform reaction
These reagents can be used to convert a methyl ketone into a carboxylic acid. This process is most efficient when the other α position (of the starting ketone) bears no protons.

Question 4

NaOH, H2O

Answer 4

Aldol addition reaction
Aqueous sodium hydroxide will cause an aldol addition reaction between two equivalents of an aldehyde or ketone to give a β-hydroxyaldehyde (or a β-hydroxyketone).

Question 5

NaOH, H2O, heat

Answer 5

Aldol condensation
Aqueous sodium hydroxide and heat will cause an aldol condensation between two equivalents of an aldehyde or ketone to give an α,β-unsaturated aldehyde (or an α,β-unsaturated ketone).

Question 6

1. NaOEt
2. H3O+

Answer 6

Claisen condensation
These reagents will cause two equivalents of an ester to undergo a condensation reaction, giving a β-ketoester. An acidic aqueous workup is required to afford the neutral product.

Question 7

1. LDA, -78ºC
2. RX

Answer 7

Alkylation
These conditions can be used to install an alkyl group at the less-substituted α position of an unsymmetrical ketone (via the kinetic enolate).

Question 8

1. NaH, 25ºC
2. RX

Answer 8

Alkylation
These conditions can be used to install an alkyl group at the more-substituted α position of an unsymmetrical ketone (via the thermodynamic enolate).

Question 9

Answer 9

Acetoacetic ester synthesis
Ethyl acetoacetate can be converted into a derivative of acetone upon treatment with ethoxide, followed by an alkyl halide, followed by hydrolysis and decarboxylation with aqueous acid and heat.

Question 10

Answer 10

Malonic ester synthesis
Diethyl malonate can be converted into a substituted carboxylic acid (more specifically, a derivative of acetic acid) upon treatment with ethoxide, followed by an alkyl halide, followed by hydrolysis and decarboxylation with aqueous acid and heat.

Question 11

1. R2CuLi
2. H3O+

Answer 11

Michael reaction
A lithium dialkylcuprate is a weak nucleophile and can serve as a Michael donor. It will undergo conjugate addition with a suitable Michael acceptor (see Table 21.2).