3-Methylbutan-2-one, (CH3)2CH-CO-CH3, is treated with one equivalent of LDA in THF at -78 degC, and then with CH3I (alkylation of the enolate at carbon). The major product is

2-methylpentan-3-one, CH3CH2-CO-CH(CH3)2

3-methylpentan-2-one, CH3-CO-CH(CH3)CH2CH3

2,4-dimethylpentan-3-one, (CH3)2CH-CO-CH(CH3)2

3,3-dimethylbutan-2-one, (CH3)3C-CO-CH3

2-methylpentan-3-one, CH3CH2-CO-CH(CH3)2

JEE Advanced levelSingle correct optionDifficulty 3 of 3g3209

3-Methylbutan-2-one, $(CH X_{3}) X_{2} CH - CO - CH X_{3}$ , is treated with one equivalent of LDA in THF at $- 78^{\circ} C$ , and then with $CH X_{3} I$ (alkylation of the enolate at carbon). The major product is

LDA at

- 78^{\circ} C

forms the kinetic enolate

CH X_{2} = C (OLi) - CH (CH X_{3}) X_{2}

by removal of the less hindered methyl H. C-Methylation at the

CH X_{2}

terminus gives

CH X_{3} CH X_{2} - CO - CH (CH X_{3}) X_{2}

, 2-methylpentan-3-one. The thermodynamic enolate would give 3,3-dimethylbutan-2-one.