10. Addition Reactions

Would you expect the following to produce an equal or unequal mixture of stereoisomers?

(c)

Predict the product(s) that would result when the following molecules are allowed to react under the following conditions: (i) 1. BH₃ 2. NaOH, H₂O₂. If there is no reaction, write 'no reaction.'

(a)

Explain why 3-methylcyclohexene should not be used as the starting material in Problem 52b.

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

(a) 1−methylcyclohexene + BH₃⋅THF then H₂O₂, OH^–

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.

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

(b) trans-4,4-dimethylpent-2-ene + BH₃⋅THF then H₂O₂, OH^–

Predict the product of the following reaction.

Show how you would accomplish the following transformations.

(b)

Devise a synthesis for each compound, starting with methylenecyclohexane and any other reagents you need.

b. cyclohexylmethanol

Predict the product of each of the following hydroboration–oxidation or oxymercuration–reduction reactions used in the modern synthetic organic chemistry literature (modified to use reagents we are used to seeing).

(c) A similar sequence was featured in the synthesis of muricadienin, a proposed precursor in the biosynthesis of solamin (Org. Lett. 2014, 16, 5886–5889).

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?

Predict the product(s) that would result when the following molecules are allowed to react under the following conditions: (i) 1. BH₃ 2. NaOH, H₂O₂ (ii) 1. Hg(OAc)₂ 2. NaBH₄ (iii) H₂SO₄ , H₂O (iv) 1. OsO₄ 2. NaHSO₃ (v) H₂O (vi) NaOH, H₂O . If there is no reaction, write 'no reaction.'

(d)

An inexperienced graduate student treated dec-5-ene with borane in THF, placed the flask in a refrigerator, and left for a party. When he returned from the party, he discovered that the refrigerator was broken and that it had gotten quite warm inside. Although all the THF had evaporated from the flask, he treated the residue with basic hydrogen peroxide. To his surprise, he recovered a fair yield of decan-1-ol. Use a mechanism to show how this reaction might have occurred. (Hint: The addition of BH₃ is reversible.)

Draw the products, including their configurations, obtained from the reaction of 1-ethylcyclohexene with the following reagents:

c. R₂BH/THF, followed by HO^–, H₂O₂, H₂O

Predict the products you would get when the following alkenes undergo (i) hydroboration–oxidation (1. BH₃ 2. NaOH, H₂O₂ or (ii) oxymercuration–reduction [1. Hg(OAc)₂, H₂O 2. NaBH₄].

(a)