Carbonyl a-Substitution Reactions - Set #II
For each of the reactions on the left, predict the major organic product. Pay particular attention to the regiochemistry and stereochemistry of the reaction.Click the mouse on the reactant molecule to view the answer;
click on the reagent to brielfy review the reaction.
An a-bromo carbonyl compound will undergo elimination in the presence of a base such as pyridine to give the a-b-unsaturated carbonyl.
Br2 in the presence of elemental phosphorus (reacts to form PBr3) will first form an acyl bromide, which enolizes and adds bromine at the a-position to give the a-bromo acid bromide. On work-up with an alcohol, the acid bromide is converted to the carboxylate ester, yielding the a-bromo ester (the Hell-Volhard-Zelinski reaction).
An enolizable carbon will loose a proton in the presence of the strong base, lithium diisopropylamide (LDA) to give an enolate anion. Reaction of this with benzeneselenyl bromide gives the intermediate organo-selenium compound. Work-up with peroxide leads to an elimination reaction, yielding the a-b-unsaturated compound. In this case, the enolizable carbon is adjacent to an ester.
An enolizable carbon will loose a proton in the presence of the strong base, lithium diisopropylamide (LDA) to give an enolate anion. Reaction of this with benzeneselenyl bromide gives the intermediate organo-selenium compound. Work-up with peroxide leads to an elimination reaction, yielding the a-b-unsaturated compound. In this case, the enolizable carbon is adjacent to a nitrile.
An a-bromo carbonyl compound will undergo elimination in the presence of a base such as pyridine to give the a-b-unsaturated carbonyl.
Br2 in the presence of elemental phosphorus (reacts to form PBr3) will first form an acyl bromide, which enolizes and adds bromine at the a-position to give the a-bromo acid bromide. On work-up with an alcohol, the acid bromide is converted to the carboxylate ester, yielding the a-bromo ester (the Hell-Volhard-Zelinski reaction).
An enolizable carbon will loose a proton in the presence of the strong base, lithium diisopropylamide (LDA) to give an enolate anion. Reaction of this with benzeneselenyl bromide gives the intermediate organo-selenium compound. Work-up with peroxide leads to an elimination reaction, yielding the a-b-unsaturated compound. In this case, the enolizable carbon is adjacent to an ester.
An enolizable carbon will loose a proton in the presence of the strong base, lithium diisopropylamide (LDA) to give an enolate anion. Reaction of this with benzeneselenyl bromide gives the intermediate organo-selenium compound. Work-up with peroxide leads to an elimination reaction, yielding the a-b-unsaturated compound. In this case, the enolizable carbon is adjacent to a nitrile.