91Ó°ÊÓ

Question: What type of pericyclic reaction is illustrated in each reaction?

Question: Draw the product formed (including stereochemistry) in each pericyclic reaction.

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.

Question: What product is formed when each compound undergoes thermal electrocyclic ring-opening or ring closure? Label each process as conrotatory or disrotatory and clearly indicate the stereochemistry around tetrahedral stereogenic centers and double bonds.

Question:Draw a stepwise mechanism for the Carroll rearrangement, a reaction that prepares aγ,δ-unsaturated carbonyl compound from aβ-keto ester and allylic alcohol in the presence ofbase.

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: What cyclic product is formed when each decatetraene undergoes thermal electrocyclic ring closure?