Quiz Competition On Pericyclic Reactions

A diene has to be able to assume an s-cis conformation in order to undergo Diels-Alder reactions, and (d) has a constrained s-trans structure

The relative configurations of the diene and dienophile are preserved in the concerted syn addition of a Diels-Alder reaction. For the stereochemistry of Diels-Alder reactions

Compound (c) is the dienophile with the best combination of low steric hindrance and a low-energy LUMO (which is caused by the electron-withdrawing anhydride residue)

The reaction is a Claisen rearrangement which is a type of [3,3] sigmatropic rearrangement

For some orbital symmetry controlled reactions, see pp. 478-5. Reaction (a) is a [2+2] cycloaddition, (b) a [3,3] sigmatropic rearrangement, (c) an electrocyclic reaction, and (d) an ene reaction.

Carbon monoxide is lost from the intermediate adduct

Reactions (a) and (b) are both [3,3] sigmatropic rearrangements, (c) an electrocyclic reaction, and (d) an ene reaction.

The products of ozonolysis followed by a reductive workup are aldehyde(s) and/or ketone(s). Note the position of the methyl substituent in the ring-opened product. For ozonolysis of alkenes

The products of ozonolysis followed by an oxidative workup are carboxylic acid(s) and/or ketone(s). Note that the position of the methyl substituent in the ring-opened product. For ozonolysis of alkenes

Electrocyclic reactions involve the cyclization of a conjugated polyene, where a pi bond is formed by the overlap of two p orbitals from adjacent atoms. This is exactly what happens in Option 1. The conjugated diene rearranges to form a cyclobutene ring with a new sigma bond between the two carbons that were originally part of the double bonds.