Chapter 25, Problem 65P

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 resultingconjugated 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.

Disiamylborane adds only once to alkynes by virtue of its two bulky secondary isoamylgroups. Disiamylborane is prepared by the reaction of BH3 # THF with an alkene.(a) Draw the structural formulas of the reagents and the products in the preparation ofdisiamylborane

Disiamylborane adds only once to alkynes by virtue of its two bulky secondary isoamylgroups. Disiamylborane is prepared by the reaction of BH3 # THF with an alkene.(a) Draw the structural formulas of the reagents and the products in the preparation ofdisiamylborane.(b) Explain why the reaction in part (a) goes only as far as the dialkylborane. Why isSia3B not formed?