91Ó°ÊÓ

When ketones are treated with Grignard reagents, an alcohol formation occurs, and an alkene product is formed by further dehydrating the alcohol.A diol compound is formed when alkene is treated with ${\text{OsO}}_{\text{4}}$and then with${\text{NaHSO}}_{\text{3}},{\text{H}}_{\text{2}}\text{O}$ .

a) When cyclohexanone is treated with methylmagnesium bromide (Grignard reagent), a methyl group is introduced, and tertiary alcohol is obtained. Further, on dehydration of tertiary alcohol by ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$generates 1-methylcyclohexene. The synthesis for this compound is shown below.

Synthesis of 1-Methylcyclohexene

b) When cyclohexanone is treated with phenylmagnesium bromide (Grignard reagent), tertiary alcohol is formed. This further dehydrates to form 1-phenylcyclohexene.

Now, 1-phenylcyclohexene is treated with ${\text{BH}}_{\text{3}}$- , and alcohol is obtained along with its enantiomer. Further, on oxidation with ${\text{CrO}}_{\text{3}}{\text{/H}}_{\text{3}}{\text{O}}^{\text{+}}$- , the desired ketone is produced. The synthesis of 2-phenylcyclohexanone is show below

Synthesis of 2-Phenylcyclohexanone

c) When cyclohexanone is treated with${\text{NaBH}}_{\text{4}}$ (a reducing agent), and then ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$, secondary alcohol is formed. Further reaction of secondary alcohol with ${\text{POCl}}_{\text{3}}\text{/pyridine}$gives cyclohexene compound.

When cyclohexene is treated with ${\text{OsO}}_{\text{4}}\text{-}$, and then with${\text{NaHSO}}_{\text{3}},{\text{H}}_{\text{2}}\text{O}$ , the product yielded is cis-1,2-cyclohexandiol compound

Synthesis of cis-1,2-Cyclohexanediol

d) Secondary alcohol is formed when cyclohexanone is treated with ${\text{NaBH}}_{\text{4}}$(a reducing agent) and then ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$.

On the treatment of cyclohexanol with${\text{PBr}}_{\text{3}}$ and then with Mg and ether, a Grignard compound is formed (${\text{C}}_{\text{6}}{\text{H}}_{\text{11}}\text{MgBr}$). This Grignard reagent on reacting with cyclohexanone and then with ${\text{H}}_{\text{3}}{\text{O}}^{\text{+}}$gives 1-Cyclohexylcyclohexanol product.

Synthesis of 1-Cyclohexylcyclohexanol