BackPredict 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
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?
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.
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.)