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Chapter 27: Q 37. (page 1101)

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

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Answer

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

Step by step solution

01

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.

02

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

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Most popular questions from this chapter

Question: (a) What product is formed by the Claisen rearrangement of compound Z? (b) Using what you have learned about ring-closing metathesis in Chapter 26, draw the product formed when the product in part (a) is treated with Grubbs catalyst. These two reactions are key steps in the synthesis of garsubellin A, a biologically active natural product that stimulates the synthesis of the neurotransmitter acetylcholine. Compounds of this sort may prove to be useful drugs for the treatment of neurodegenerative diseases such as Alzheimer’s disease.

Question: What type of cycloaddition occurs in Reaction [1]? Draw the product of a similar process in Reaction [2]. Would you predict that these reactions occur under thermal or photochemical conditions?

Question:Draw the product (including stereochemistry) formed from each pair ofreactants in a thermal [4 + 2] cycloaddition reaction.

Question:(a) Draw the product of the following [4 + 2] cycloaddition, which was carried out in the early stages of the synthesis of the alkaloid reserpine (Problem 22.83). Indicate the stereochemistry at any newly formed stereogenic centers. (b) Draw the porbitals of the alkene and the terminal carbons of the conjugated diene, and show how the orientation of the reactants and orbital overlap lead to the observed stereochemistry.

Question: When both carbons ortho to the aryl oxygen are not bonded to hydrogen, an allyl aryl ether rearranges to a para-substituted phenol. Draw a stepwise mechanism for the following reaction, which contains two [3,3] sigmatropic rearrangements.
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