Aldehydes and ketones that possess a,b-unsaturation, like uracil, exhibit unique

Chapter 23, Problem 23

(choose chapter or problem)

Aldehydes and ketones that possess \(\alpha, \beta-\text { unsaturation }\), like uracil, exhibit unique reactivity at the \(\beta\) position. The reactivity of the \(\beta\) position is called a conjugate addition or a 1,4-addition, because the nucleophile and the proton are added across the ends of a conjugated \(\pi\) system. This is generally accomplished using mildly basic nucleophiles. This differs from the competing 1,2-addition, where highly reactive nucleophiles tend to favor direct attack at the carbonyl. In step A, we have attack of the thiolate of the enzyme on the \(\beta\) carbon of the dUMP. Which of the following reagents could achieve conjugate addition on the dUMP (cytosine fragment) in Step A?

(a) \(\mathrm{LiAlH}_{4}\)

(b) \({\left[\mathrm{Cu}\left(\mathrm{CH}_{3} \mathrm{CH}_{2}\right)_{2}\right] \mathrm{Li}}\)

(c) \(\mathrm{Mg}\left(\mathrm{CH}_{2} \mathrm{CH}_{3}\right) \mathrm{Br}\)

(d) \(\mathrm{LiCH}_{2} \mathrm{CH}_{3}\)

Equation Transcription:

Text Transcription:

\alpha, \beta- unsaturation

\beta

\beta

\pi

\beta

LiAlH4

[Cu(CH3CH2)2]Li

Mg(CH2CH3)Br

LiCH2CH3