Disiamylborane adds only once to alkynes by virtue of its two bulky secondary isoamyl groups. 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 of disiamylborane.
b. Explain why the reaction in part (a) goes only as far as the dialkylborane. Why is Sia₃B not formed?

How can the following compounds be synthesized, starting with a hydrocarbon that has the same number of carbons as the desired product?

b. CH₃CH₂CH₂CH₂OH

We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.

(c)

What reagents are needed to synthesize the following alcohols?

What is the major product obtained from hydroboration–oxidation of the following alkenes?

a. 2-methyl-2-butene

In the hydroboration of 1-methylcyclopentene shown in Solved Problem 8-3, the reagents are achiral, and the products are chiral. The product is a racemic mixture of trans-2-­methylcyclopentanol, but only one enantiomer is shown. Show how the other enantiomer is formed.

Show how you would synthesize each compound using methylenecyclohexane as your starting material.

(c)

When (Z)-3-methylhex-3-ene undergoes hydroboration–oxidation, two isomeric ­products are formed. Give their structures, and label each asymmetric carbon atom as (R) or (S). What is the relationship between these isomers?

When 1,2-dimethylcyclopentene undergoes hydroboration–oxidation, one diastereomer of the product predominates. Show why this addition is stereospecific, and predict the stereochemistry of the major product.