The syntheses shown here are unlikely to occur as written. What is wrong with each? (FIGURE CANN

The syntheses shown here are unlikely to occur as written....

Key Concepts

Reagent Choice and Reaction Conditions

The selection of reagents and the conditions under which reactions are performed are key elements of reliable synthesis planning. It is important to determine if the reagents are compatible with the functional groups in the substrate, whether they can provide the necessary activation, and if the conditions (solvent, temperature, time) are suitable to drive the reaction to completion without promoting side reactions.

Step Order and Strategic Sequence

The order in which transformations are carried out can critically impact the overall success of a synthetic route. Each step must be planned so that reactive intermediates are generated and utilized efficiently, and so that earlier steps do not compromise or deactivate groups needed for later reactions. An incorrect sequence can lead to functional group incompatibility or the failure of subsequent steps.

Mechanistic Feasibility

This concept involves ensuring that each proposed transformation in a synthetic sequence is consistent with accepted reaction mechanisms. It requires assessing whether reaction intermediates are likely to form under the given conditions, if the reactants possess the appropriate reactivity (nucleophilic or electrophilic character), and if any steric or electronic factors might impede the progress of the reaction.

Functional Group Compatibility

In multi-step syntheses, it is crucial to evaluate the reactivity of different functional groups present in the molecules. Some functional groups may be too reactive under the planned conditions and can interfere with the desired transformations. Often, protective groups need to be applied to vulnerable functionalities to prevent side reactions or degradation.

Transcript

00:01 Okay, this problem is asking us to analyze these reactions and say what is wrong with them.

00:05 So if we zoom into the first one, we can see that we have an alkyl fluoride reacting with magnesium and acid workup to generate a propane molecule.

00:12 So is this correct? the answer is no, because alkyl fluorides have a very specific or very different reactivity with magnesium than do alkyl chlorides, alkyl chlorides, alkyl bromides, and alkyl iodides.

00:22 So if we were to create a greenerd, then we would have an acid workup, which would generate propane.

00:28 So, ideally, we want a greenered reagent and then acidify it using acid workup to generate propane.

00:34 But fluorine and magnesium do not combine to make a greenered reagent.

00:37 Instead, we would want something like chlorine or bromine or iodine.

00:42 So i'm going to just write bromine.

00:44 Okay, that would generate a greenerid reagent, and then we can make propane.

00:48 Okay, next step, we have an alkene reaction with nbs, and then we have our product.

00:54 Okay, so is this the correct reaction? the answer is no.

00:58 Product is not correct.

01:01 So let's look at our started material.

01:04 Our starting material has an alkene, and then one carbon away is our allelic carbon.

01:10 So surface level, if we were to have a radical here and we had a bromine here, this would be our reaction, which seems correct because we have the generation of the correct product off of that.

01:20 But this radical is not considered to be the most reactive.

01:24 We would want a better situation in which we have a bromine, the position of the roaming in a different spot because of the position of the radical being more reactive.

01:33 So, for example, let's say i have my alken.

01:37 I have two options as far as the allilic carbon in which the radical is associated with.

01:41 I can either have a radical here or i can have a radical here.

01:45 So which one is considered the most stable? the answer relies on the carbons in which they're attached to.

01:52 So i have a radical here.

01:54 That's one option.

01:55 That radical is on a one, two, secondary carbon...

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