10. Addition Reactions

Show how you would accomplish the following synthetic conversions.

a. but-1-ene → butan-1-ol

Show how you would accomplish the following synthetic conversions.

(b) but-1-ene → butan-2-ol

Draw the products of the following reactions, including their configurations:

The bulky borane 9-BBN was developed to enhance the selectivity of hydroboration. In this example, 9-BBN adds to the less hindered carbon with 99.3% regioselectivity, compared with only 57% for diborane.

a. Show the two organic products generated when the trialkylborane is oxidized with H₂O₂/NaOH.

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (vi) 1. BH₃ 2. H₂O₂, NaOH

(b)

Show a mechanism for the formation of one isomer in each of the reactions in Assessment 9.1.

(c)

Which of the following reagents can be used to convert $1-\mathrm{pentyne}$ into an $\mathrm{aldehyde}$ via hydroboration-oxidation?

Predict the product(s) that would result when the alkenes shown here are allowed to react under the following conditions: (vi) 1. BH₃ 2. H₂O₂, NaOH

(g)

Indentify the mechanism of reaction and predict the product.

a. Starting with 3-methyl-1-butyne, how can you prepare the following alcohols?

  1. 2-methyl-2-butanol

b. In each case, a second alcohol would also be obtained. What alcohol would it be?

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?

Predict the major products of the following reactions. Include stereochemistry where applicable.

(c)

Suggest an alkene to undergo hydroboration–oxidation (1. BH₃ 2. NaOH, H₂O₂) to give exclusively the alcohols shown. Pay close attention to the relative (but not absolute) stereochemical outcome.

(c)

Show how each of the following compounds can be synthesized from an alkene:

c.

Draw the product or products that will be obtained from the reaction of cis-2-butene and trans-2-butene with each of the following reagents. If a product can exist as stereoisomers, show which stereoisomers are formed.

2. BH₃/THF, followed by HO^-, H₂O₂, H₂O