Question

Question: The bicyclic alkene P can be prepared by thermal electrocyclic ring closure from cyclodecadiene Q or by photochemical electrocyclic ring closure from cyclodecadiene R.Draw the structures of Q and R, and indicate the stereochemistry of the process by which each reaction occurs.

Short answer

Answer

• Preparation of product P by thermal electrocyclic ring closure from cyclodecadiene Q

Step-by-step solution

Electrocyclic reactions stereochemistry

Electrocyclic reactions are highly stereospecific. The stereochemistry of the product is dependent on whether the reaction is thermally induced or photo-induced.

Retrosynthetic analysis of the target molecule.

• It is an electrocyclic ring closure reaction of the compound with two conjugated double bonds.
• Since the reactant has two double bonds, the product will have one double bond and one additional sigma bond.

(a)

• The ring closure occurs through a conrotatory process following Woodward-Hoffmann’s rules for thermal conditions.

• The trans-cyclodeca-1,3-diene (Q) undergoes con-rotation in the presence of thermal condition to form a cis-product (P)

Synthesis of P from Q

(b)

• The ring closure occurs through a disrotatory process following Woodward-Hoffmann’s rules for photochemical conditions.

• The cis-cyclodeca-1,3-diene (R) undergoes dis-rotation in the presence of photochemical conditions to form a cis-product (P)

Synthesis of P from R