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Chapter 27: Q 57. (page 1104)

Question: Show how the following starting material is converted to the given product by a series of two pericyclic reactions. Account for the observed stereochemistry.

Short Answer

Expert verified

Answer

Step 1- Ring-opening

Step 2- Ring-closing

Step by step solution

01

Ring-opening reaction

The smaller ring is less stable than the large rings. On heating, the small ring undergoes a ring-opening reaction by following the conrotation of the molecular orbitals.

02

Ring-closing reaction

On heating, the 6 π-molecular orbitals undergo a ring-closing reaction by following disrotation of the molecular orbitals.

03

Explanation of the given reaction

The first step is the ring-opening reaction as the smaller rings are strained; hence they undergo a ring-opening reaction quickly even on less heating.

In the next step, the two reactants undergo a ring-closing reaction by following the disrotation of molecular orbitals.

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Most popular questions from this chapter

Question: Classify each reaction as an electrocyclic reaction, a cycloaddition, or a sigmatropic rearrangement. Label the σ bonds that are broken or formed in each reaction.

Question:(a) What product is formed from the [1,7] sigmatropic rearrangement of a deuterium in the following triene?

(b) Does this reaction proceed in a suprafacial or antarafacial manner under

thermal conditions?

(c) Does this reaction proceed in a suprafacial or antarafacial manner under

photochemical conditions?

Question: The endiandric acids comprise a group of unsaturated carboxylic acids isolated from a tree that grows in the rain forests of eastern Australia. The methyl esters of endiandric acids D and E have been prepared from polyene Y by a series of two successive electrocyclic reactions: thermal ring closure of the conjugated tetraene followed by ring closure of the resulting conjugated triene. (a) Draw the structures (including stereochemistry) of the methyl esters of endiandric acids D and E. (b) The methyl ester of endiandric acid E undergoes an intramolecular [4 + 2] cycloaddition to form the methyl ester of endiandric acid A. Propose a possible structure for endiandric acid A.

Question: Classify each pericyclic reaction as an electrocyclic reaction, cycloaddition, or sigmatropic rearrangement. Indicate whether the stereochemistry is conrotatory, disrotatory, suprafacial, or antarafacial.

Question: How can X be prepared from a constitutional isomer by a series of [2+2]cycloaddition reactions? Interest in molecules that contain several cyclobutane rings fused together has been fueled by the discovery of pentacycloanammoxic acid methyl ester, a lipid isolated from the membrane of organelles in the bacterium Candidatus Brocadia anammoxidans. The role of this unusual natural product is as yet unknown.
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