13. Alcohols and Carbonyl Compounds

Which of the following solvents are reasonable choices for a Grignard reaction? Justify your choices. [Hint: Carbonyls are good electrophiles.]

Often, compounds can be synthesized by more than one method. Show how this 3° alcohol can be made from the following:

(c) an ester

Show how you would synthesize the following compound from alkyl halides, vinyl halides, and aryl halides containing no more than six carbon atoms.

(a) octane

Give the expected products of the following reactions. Include a protonation step where necessary.

(a) 2,2-dimethyloxirane + isopropylmagnesium bromide

(b) propylene oxide + n-butyllithium

(c) cyclopentyloxirane + ethyllithium

A chemist failed to generate the alcohol using the reaction shown here.

(a) Suggest a reason why this reaction did not work as written.

Show how you would synthesize the following:

f. 2,5-dimethylhexane from a four-carbon alkyl halide

Show how you would synthesize following tertiary alcohol by adding an appropriate Grignard reagent to a ketone.

b. Ph₃COH

Addition to an epoxide occurs via an S_N2 reaction, but the stereochemistry of the epoxide is retained in the following reaction. Why?

A laboratory student added 1-bromobutane to a flask containing dry ether and magnesium turnings. An exothermic reaction resulted, and the ether boiled vigorously for several minutes. Then she added acetone to the reaction mixture and the ether boiled even more vigorously. She added dilute acid to the mixture and separated the layers. She evaporated the ether layer, and distilled a liquid that boiled at 143 °C. GC–MS analysis of the distillate showed one major product with a few minor impurities. The mass spectrum of the major product is shown here.

(a) Draw out the reactions that took place and show the product that was formed.

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Show how you would synthesize the following primary alcohol by adding an appropriate Grignard reagent to formaldehyde.

(c)

Predict the product of the following epoxide opening reactions.

(a)

Predict the major products of the following reactions, including stereochemistry where appropriate.

(h) cyclooctylmethanol + CH₃CH₂MgBr

(i) potassium tert-butoxide + methyl iodide

(j) sodium methoxide + tert-butyl iodide

Dimerization is a side reaction that occurs during the preparation of a Grignard reagent. Propose a mechanism that accounts for the formation of the dimer.

Grignard reagents react slowly with oxetane to produce primary alcohols. Propose a mechanism for this reaction, and suggest why oxetane reacts with Grignard reagents even though most ethers do not.

A formate ester, such as ethyl formate, reacts with an excess of a Grignard reagent to give (after protonation) secondary alcohols with two identical alkyl groups.

(a) Propose a mechanism to show how the reaction of ethyl formate with an excess of allylmagnesium bromide gives, after protonation, hepta-1,6-dien-4-ol.