Chapter 27: Q 47. (page 1102)
Question: What product is formed from the sigmatropic rearrangement of the following unsaturated ether?

Short Answer
Answer

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Chapter 27: Q 47. (page 1102)
Question: What product is formed from the sigmatropic rearrangement of the following unsaturated ether?

Answer

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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: Vitamin , the most abundant of the D vitamins, is synthesized from 7-dehydrocholesterol, a compound found in milk and fatty fish, such as salmon and mackerel. When the skin is exposed to sunlight, a photochemical electrocyclic ring-opening forms provitamin , which is then converted to vitamin by a sigmatropic rearrangement (Section 27.5). Draw the structure of provitamin .

Question: What product is formed when each compound undergoes a photochemical electrocyclic reaction? Label each process as conrotatory or disrotatory and clearly indicate the stereochemistry around tetrahedral stereogenic centers and double bonds.

Question: Draw the product formed when diene M undergoes disrotatory cyclization. Indicate the stereochemistry at new hybridized carbons. Will the reaction occur under thermal or photochemical conditions?

Question: Draw the products of each reaction.

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