Question

Question: Show how you would convert pent-1-eneto each of the following compounds. You may use any additional reagents and solvents you need.

(a) 2-methoxypentane

(b) 1-methoxypentane

(c) 1-methoxypentan-2-ol

(d) 2-methoxypentan-1-ol

(e) 1-phenylpentan-2-ol

(f) 2-methoxy-1-phenylpentane

Short answer

Peroxy acids can be used to convert alkenes to epoxides. The epoxides are known to open to a glycol if the reaction occurs in an aqueous medium. For this reason, strong acids are avoided for the synthesis of epoxides. meta-chloroperoxybenzoic acid (mCPBA) can be used for epoxidations because of its desirable soluble properties. mCPBA is weakly acidic peroxy acid and is soluble in an aprotic solvent like dichloromethane. The reaction proceeds in a one-step concerted manner where the stereochemistry of any substituents around the double bond is maintained.

Step-by-step solution

Peroxyacid epoxidation

Peroxy acids can be used to convert alkenes to epoxides. The epoxides are known to open to a glycol if the reaction occurs in an aqueous medium. For this reason, strong acids are avoided for the synthesis of epoxides. meta-chloroperoxybenzoic acid (mCPBA) can be used for epoxidations because of its desirable soluble properties. mCPBA is weakly acidic peroxy acid and is soluble in an aprotic solvent like dichloromethane. The reaction proceeds in a one-step concerted manner where the stereochemistry of any substituents around the double bond is maintained.

Alkoxymercuration-demercuration

This process adds a molecule of an alcohol (-OR group) across the double bond (more substituted) of an alkene. The product formed is an ether.

Conversion

(a) pent-1-ene undergoes alkoxymercuration-demercuration process to form 2-methoxypentane.

(b) pent-1-ene reacts with HBr in presence of a peroxide to give 1-bromopentane which further reacts with sodium methoxide to form 1-methoxypentane.

(c) pent-1-ene reacts with mCPBA to give 2-propyloxirane which further reacts to form 1-methoxypentan-2-ol.

(d) pent-1-ene reacts with mCPBA to give 2-propyloxirane which further reacts to form 2-methoxypentan-1-ol.

(e) pent-1-ene reacts with mCPBA to give 2-propyloxirane which further reacts with phenyl magnesium bromide and then hydrolysis forms 1-phenyl-pentan-2-ol.

(f) pent-1-ene reacts with mCPBA to give 2-propyloxirane which further reacts with phenyl magnesium bromide and then the further reaction form the desired product 2-methoxy-1-phenyl-pentane.