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Be sure to answer all parts. identify a, b, and c, intermediates in the synthesis of the five-membered ring called an α−methylene−γ−butyrolactone. this heterocyclic ring system is present in some antitumor agents. do not draw lone pairs in your answers. 23191 draw structure ... draw structure ... draw structure ... a b c

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transitionstate
The complete reaction along with intermediates is given below, with each step highlighted in different color.

Step 1:
           In this step an acidic proton at alpha position is abstracted from lactone moiety and corresponding enolate is formed, which is resonance stabilized. Both structures are shown. In this case LDA (Lithium diisopropylamide) acts as a base.

Step 2:
           The enolate formed attacks on Methyl Iodide, as Iodide being greater in size is a good leaving group and alpha methyl moiety is generated.

Step 3:
           This step is acid catalyzed Bromination. Bromine is added at alpha position.

Step 4: 
           This is elimination reaction and is according to Hofmann's Rule. Here less substituted alkene is generated. 
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