Suggest the most appropriate method for each of the following&...

Question

Suggest the most appropriate method for each of the following laboratory syntheses. In each case, suggest both a chromium reagent and a chromium-free reagent.

(d) cyclopentanol → 1-ethylcyclopentanol (two steps)

(e) cyclopentylmethanol → 1-cyclopentylpropan-1-ol (two steps)

Accepted Answer

All right. Hello everyone. So this question says to propose a reaction pathway for the following syntheses. If the reaction involves oxidation reactions provide both a chromium reagent and a chromium free reagent, lets go ahead and start with part one. Now for both parts, I am going to go ahead and draw both the starting material and the intended products. First, we have cyclohexane all as our starting material and one methyl cyclohexane as our final product after two steps. So the starting material is cyclohexane, all which is a six carbon parent chain, more specifically a six carbon ring with a hydroxy group attached and our product is one methyl cyclohexane all. So it looks very similar to cyclohexane, all except there is a methyl substituent on the same carbon that has the hydroxy group. So when comparing the structures of the starting material in the product, the only thing that's changing is the addition of a methyl substituent. And so the important thing to, to keep into consideration here is that we have the formation or we've created a new carbon carbon bond when going from the starting material to the product because we're creating a new carbon carbon bond. One of the most convenient ways to achieve this is using organo melic reagents, more specifically a green yard reagent. Now recall that green yard reagents can most effectively be used for the nucleic addition of an ocho group on to aldehydes and ketones. Because after the protonation of the carbon oxygen, the product is a more substituted alcohol. So that's where the two steps come from. In this case, the first of which is oxidation to go from alcohol to Carboni. In this case, the ketone and then we can set up our Green Yard reaction or green yard rage. So because we have two steps, I'm going to go ahead and make space in between the starting material and the product. So first for the oxidation, we can use a chromium reagent such as H two cro four, this ultimately converts the hydroxy group into a car bono meeting our intermediate is now cyclohexane. And so now that we have cyclohexane, no, we can go ahead and add a methyl group to this intermediate using a green yard reagent. So when it comes to the second step in reality, there are going to be two individual steps to achieve the pronated alcohol product. The first of which is the green yard reagent, for example, methyl magnesium bromide who install the correct R group and this is done in the presence of ether as a solvent. However, an additional step is needed in which H 30 positive is added. This is because without the addition of some acid, the oxide ion that formed after the addition of the green yard, we would not be proton. So the second step is necessary to produce the alcohol product. So now this completes the reaction sequence for part one, but we do have to add the chromium free reagent as well for the oxidation step. An effective example of a chromium free reagent that can be used is sodium hypochlorite. That's naoc and acetic acid. That's ch three Coh. All right. So from here, let's proceed with part two. Now, for part two, the reaction in question is going from cyclo heel methanol to one cyclo heel ethanol. So let's draw that our starting material is Cyclo Hexon Mehan. So we have a hydroxy group and a six carbon ring branching off of the same carbon. Our product. On the other hand, is one cyclo heel ethanol. So here we have a six carbon ring and a hydroxy group both connecting to carbon number one of a two carbon chain. All right. So once again, the difference here is that one additional carbon has been added to the overall structure. This means that we can set up the use of a Green Yard regent in the same way that we did. For part one, the difference however, is going to lie in the oxidation step beforehand because the starting material this time around is a primary alcohol recall it when it comes to a primary alcohols or primary alcohols. The specific reagent used for the oxidation step is very important because it's, it's possible to produce either a carboxylic acid or an aldehyde depending on whether or not you're using a stronger or a more mild oxidizing agent because we're trying to only convert this alcohol into an aldehyde. A mild oxidizing agent is going to be necessary here, a stronger oxidizing agent would produce a carboxylic acid instead. So once again, I'm just going to make some space in the center. And for the first step, we only need a more mild reducing agent, such as for example, PC C, that's Pyridium chloro chromate that converts our primary alcohol into an aldehyde which can then undergo nucleic attack using a green yard reagent. So now the green yard reaction can be set up in much the same way as we did. For part one, in the first step, we can use methyl magnesium bromide in the presence of ether to install one additional carbon. And then in the second step, we add H 30 positive as a source of acid to proton the oxide ion and create the alcohol product. So now this concludes the reaction sequence for part two. So now let's go ahead and add the chromium free reagent. An example of a chromium free reagent that will achieve the oxidation of a primary alcohol into an aldehyde is using one equivalent of sodium hypochlorite with tempo and there you have it. Now, our answer is complete for parts one and two. And so with that being said, if you watch this video all the way through, thank you so very much. And I hope you found this helpful.

Suggest the most appropriate method for each of the following laboratory syntheses. In each case, suggest both a chromium reagent and a chromium-free reagent.
(d) cyclopentanol → 1-ethylcyclopentanol (two steps)
(e) cyclopentylmethanol → 1-cyclopentylpropan-1-ol (two steps)

Key Concepts

Reagents in Organic Synthesis

Functional Group Transformation

Multi-step Synthesis

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