Regioselective reactions

Question 1

Two reactions for the hydration of double bonds

Answer 1

Hydroboration and Oxymecuration/reduction

Question 2

Reagents and product of hydroboration

Answer 2

Alkene to give a primary alcohol. Uses BH3, THF and then H2O2, NaOH

Question 3

Reagents and products of oxymercuration

Answer 3

Alkene to give a secondary alcohol. Uses Hg(OAc)2 and NaBH4

Question 4

Addition of HBr to alkene mechanisms and their products

Answer 4

Radical and ionic. Ionic gives a secondary alkyl halide and radical a primary alkyl halide

Question 5

Radical mechanism for the addition of HBr

Answer 5

See notes

Question 6

Baeyer-Villiger oxidation, reagents and outline

Answer 6

Oxidation of ketones to esters and cyclic ketones to lactones using MCPBA

Question 7

What is MCPBA

Answer 7

metachloroperbenzoic acid

Question 8

Where is the oxygen inserted using Baeyer-Villiger oxidation

Answer 8

Between the carbonyl and the most substituted alpha carbon

Question 9

Baeyer-Villiger oxidation mechanism

Answer 9

See notes

Question 10

Beckmann rearrangement. Reagents and outline

Answer 10

Insertion of nitrogen next to the carbonyl group to form an amide. Using an amino alcohol and a lewis acid (usually H2SO4 or Al2O3)

Question 11

Reaction scheme of the Beckmann rearrangement

Answer 11

Addition of the amino alcohol to give an oxime, addition of H2SO4 to give the amide

Question 12

Which is the migrating group of the oxime during Beckmann rearrangement

Answer 12

The one trans to the OH group

Question 13

What property of the nucleophile determines if addition to an enone is conjugated or direct

Answer 13

Strong bases attack directly, weak bases attack conjugately

Question 14

‘trapping’ an enolate during conjugate addition

Answer 14

Addition of an alkyl halide instead of acidic workup following the initial addition. This is then a 1,2 addition of a second alkyl chain.

Question 15

Acidic and basic attack on epoxides

Answer 15

Under basic conditions, the less sterically hindered carbon is attacked. Under acidic conditions, the more hindered carbon is attacked

Question 16

Outline the reaction between amines and epoxides

Answer 16

Occurs under basic conditions and tends to stop after the first addition (the product is less nucleophilic than the starting material).

Question 17

Synthesis of alpha hydroxy acids using nitriles

Answer 17

starts with an aldehyde. Reaction with NaCN then reaction of the nitrile with H+ and H2O to give the alpha hydroxy acid

Question 18

1,2 electrophilic addition to an aldehyde

Answer 18

Uses dithianes. Reaction with a dithiol under acidic conditions to give the dithiane, loss of the acidic proton using BuLi and THF at -70 degrees. Addition of an electrophile and loss of the dithiane using Hg2+, H2O

Question 19

Using nitroalkanes to prepare 1,4 products

Answer 19

Conjugate addition of the nitro species to an enone, basic conditions form an iminium intermediate, ozonolysis using O3 and MeOH gives a 1,4 dicarbonyl

Question 20

Mechanism to product a 1,4 dicarbonyl from a nitro species using an enone

Answer 20

See notes