Pericyclic Reactions Part 3: Sigmatropic Shifts (Cope Rearrangement, Claisen Rearrangement)

The video tutorial explores cycloaddition reactions, focusing on the Diels Alder reaction and its formation of sigma bonds. It introduces sigmatropic shifts, highlighting their differences from cycloadditions, and explains the concept of three-three shifts with examples. The tutorial discusses the COPE rearrangement and methods to enhance sigmatropic shifts, such as incorporating ring strain and stabilizing products. It also covers the Claisen rearrangement, its variations, and applications in synthesizing gamma-delta unsaturated carbonyl compounds.

What distinguishes sigmatropic shifts from cycloaddition reactions?

• Sigmatropic shifts involve breaking and reforming a sigma bond.

• Cycloaddition reactions are not subject to the 4n+2 rule.

• Sigmatropic shifts occur in multiple steps.

• Cycloaddition reactions involve only pi bonds.

Why is a 1,3-shift considered unfavorable?

• It results in a loss of aromaticity.

• It requires a high temperature to proceed.

• It involves an anti-aromatic number of electrons.

• It forms a less stable product.

In the context of sigmatropic shifts, what does a degenerate system imply?

• The product and starting material are indistinguishable without labeling.

• The product is different from the starting material.

• The reaction has a high yield.

• The reaction is irreversible.

What is a key feature of the Cope rearrangement?

• It involves the formation of a new pi bond.

• It is not useful in synthetic chemistry.

• It requires low temperatures to proceed.

• It can be modified to become more favorable.

How does the oxy-Cope rearrangement differ from the standard Cope rearrangement?

• It involves the formation of a carbonyl group.

• It does not involve any sigma bond shifts.

• It requires a catalyst to proceed.

• It is less favorable than the standard Cope rearrangement.

What is the driving force behind the Claisen rearrangement?

• Formation of a stable carbonyl compound.

• Breaking of aromaticity.

• Formation of a new sigma bond.

• Loss of conjugation.

Which type of shift involves a hydride moving from one carbon to another?

• Oxy-Cope rearrangement

• 1,5-hydride shift

• 1,3-shift

• 3,3-shift