How would you prepare pentanal from the following starting...

How would you prepare pentanal from the following starting materials? (a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}$ (b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{2}$ (c) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}_{3}$ (d) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{2}$

How would you prepare pentanal from the following starting materials?
(a) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}$
(b) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{2}$
(c) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CO}_{2} \mathrm{CH}_{3}$
(d) $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}=\mathrm{CH}_{2}$

Key Concepts

Hydroformylation Reaction

Hydroformylation is a catalytic reaction in which an alkene is reacted with carbon monoxide and hydrogen to form an aldehyde. This reaction, often catalyzed by transition metals such as rhodium or cobalt, involves the addition of a formyl group and a hydrogen atom across the carbon–carbon double bond, thereby converting an alkene into an aldehyde with one more carbon than the starting material.

Partial Reduction of Esters

Esters can be reduced to aldehydes selectively by using reducing agents that stop at the aldehyde stage rather than continuing the reduction to the corresponding alcohol. A common reagent for this transformation is diisobutylaluminum hydride (DIBAL-H), which, when used at low temperatures, can reduce an ester to an aldehyde without further reducing it to an alcohol.

Controlled Oxidation of Primary Alcohols

This concept involves oxidizing a primary alcohol to an aldehyde using a mild oxidizing agent so that the reaction stops at the aldehyde stage and does not proceed to the carboxylic acid. Reagents such as PCC (pyridinium chlorochromate) are typically used to achieve this selective oxidation under carefully controlled conditions.

Ozonolysis of Alkenes

Ozonolysis is a reaction that cleaves carbon–carbon double bonds by treatment with ozone, leading to the formation of carbonyl compounds. The method is useful in transforming alkenes into aldehydes or ketones depending on the substitution pattern of the alkene. When applied to terminal alkenes, one of the cleavage products can be formaldehyde, while the other fragment becomes an aldehyde with a longer carbon chain.

Transcript

00:01 This question here asks us to, we're given various certain materials, and we'll ask to form pentanyl.

00:06 And so that's a five, five carbons, one, two, three, four five is shown here with a co double bond at the end, an aldehyde.

00:15 And so the first structure that we're given to try and get to this form is the same thing, but instead of an aldehyde, we have an alcohol.

00:24 And so to get from here to here, the first thing that we need to, we really just need to do one thing.

00:28 We need to oxidize the alcohol into an aldehyde, but not pass that into a carboxylic acid.

00:35 So we need a somewhat mild reagent.

00:38 And the one that this book proposes, there's other ones that also work, is desmartin periodine.

00:46 And so that's often labeled as dmp.

00:51 And so this is just a one -step partial oxidation to aldehyde.

00:58 The next one, to again, trying to get to pentanow, we are given the starting material of one, two, three, four, five carbon chain, then six.

01:15 So this is hexene with the double bond at one.

01:23 And so this requires a little bit of realization that we have six carbons here and five carbons here.

01:30 So we need to have some reaction that breaks a double bond or breaks the carbon carbon bond.

01:34 And we happen to know one that breaks a double bond and also very conveniently puts an oxygen there in its place.

01:43 And so the one that does that is ozonolysis...

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