Question

You saw in the practiceproblems that certain nitriles, when substituted withelectron? withdrawing groups, can actas dienophiles in Diels?Alder reactions. The compoundillustrated below undergoes an intramolecularDiels?Alder reaction when heated.Of course intramolecular reactions are usually faster thanintermolecular ones, and in this case the reaction proceedsextraordinarily rapidly withoutelectron?withdrawing groups on thenitrile dienophile.

1. Draw a curved?arrowmechanism that leads to the most likely product of thisintramolecular Diels?Alderreaction.

   

2. The product of this reaction isactually not stable as drawn and immediately tautomerizes. Draw theactual final product of the reaction. (Hint: remembertautomerization from your study of alkyne reactions, and note thatnitrogen as well as oxygen compounds can behave in this way.) Whatis the driving force for this seemingly disfavored tautomerization(i.e., why is it actually more favorable in the

You saw in the practice problems that certain nitriles, when substituted with electron? withdrawing groups, can act as dienophiles in Diels?Alder reactions. The compound illustrated below undergoes an intramolecular Diels? Alder reaction when heated. Of course intramolecular reactions are usually faster than intermolecular ones, and in this case the reaction proceeds extraordinarily rapidly without electron? withdrawing groups on the nitrile dienophile. Draw a curved?arrow mechanism that leads to the most likely product of this intramolecular Diels?Alder reaction. The product of this reaction is actually not stable as drawn and immediately tautomerizes. Draw the actual final product of the reaction. (Hint: remember tautomerization from your study of alkyne reactions, and note that nitrogen as well as oxygen compounds can behave in this way.) What is the driving force for this seemingly disfavored tautomerization (i.e., why is it actually more favorable in the "enol" form than the "keto" form)?