10. Addition Reactions

Hydroboration, an electrophilic addition reaction like those studied in Section 21.4, only gives 1,2-addition to buta-1,3-diene, regardless of temperature. Why?

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)

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

(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.

(b)

Suggest a reagent and a reactant that could be combined to make each of the following alcohols.

(a)

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)

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).

(b) A two-step hydroboration–oxidation was used to prepare a silanediol peptidomimetic as a serine protease inhibitor (Org. Lett. 2012, 14, 4422–4425).

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).

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?

What stereoisomers are obtained from hydroboration–oxidation of the following compounds? Assign an R or S configuration to each asymmetric center.

a. cyclohexene

b. 1-ethylcyclohexene

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

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