Publication

A novel aldol condensation alternative: a,b-unsaturated aldehydes from 3-hydroxy-1-alkynes via dihydrodioxepins

Manfred Schlosser
1998
Journal Articles

Abstract

The controlled aldol condensation between an aliph. ketone and an acetaldehyde equiv. remains a challenge. One soln. to this evergreen problem consists of the nucleophilic addn. of acetylene to the ketone and the subsequent isomerization of the resulting 3-hydroxy-1-alkyne to the corresponding 2-alkenal. So far, however, the latter step could only be executed with acid-insensitive substrates. The authors now present a milder, three-step method which extends the scope of the procedure considerably. In the first step, the 3-hydroxy-1-alkynes RCMeOHC.tplbond.CH (R = Me, Ph, Me2CH:CHCH2CH2, Q, CH2:CH, HC.tplbond.C) are converted into 2-propynyl ethylene glycol monoethers RCMe(OCH2CH2OH)C.tplbond.CH; these then undergo base-catalyzed cyclization to give the dihydro-1,4-dioxepins (I and II; R = same as above), which are hydrolyzed in acidic medium in the third and final step to give ketones RCMeOHCOMe (R = same as above) and a,b-unsatd. aldehydes RCMe:CHCHO (R = same as above), resp. Thus, RCMe(OCH2CH2OH)C.tplbond.CH (R = Q) (prepn. given) was treated with Me3COK in Me3COH for 12 h at 85 Deg to give a 4:96 mixt. of I (R = Q) and II (R = Q) in 95% yield. II (R = Q) was hydrolyzed by 6 M HCl in THF under reflux for 5 h to give 90% RCMe:CHCHO (R = Q). [on SciFinder (R)]

Official source

https://infoscience.epfl.ch/entities/publication/1f5642ae-3532-490c-b38d-4c49f30f647c

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Manfred Schlosser
1998
Journal Articles

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/1f5642ae-3532-490c-b38d-4c49f30f647c

About this result

Related concepts (24)

Protecting group

A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis. In many preparations of delicate organic compounds, some specific parts of their molecules cannot survive the required reagents or chemical environments. Then, these parts, or groups, must be protected. For example, lithium aluminium hydride is a highly reactive but useful reagent capable of reducing esters to alcohols.

Aldol condensation

An aldol condensation is a condensation reaction in organic chemistry in which two carbonyl moieties (of aldehydes or ketones) react to form a β-hydroxyaldehyde or β-hydroxyketone (an aldol reaction), and this is then followed by dehydration to give a conjugated enone. The overall reaction equation is as follows (where the Rs can be H) Aldol condensations are important in organic synthesis and biochemistry as ways to form carbon–carbon bonds.

Aldol reaction

The aldol reaction (aldol addition) is a reaction that combines two carbonyl compounds (aldehydes or ketones) to form a new β-hydroxy carbonyl compound. These products are known as aldols, from the aldehyde + alcohol, a structural motif seen in many of the products. The use of aldehyde in the name comes from its discovery history, where aldehydes were first used in the reaction and not ketones. Aldol structural units are found in many important molecules, whether naturally occurring or synthetic.