A Claisen condensation between two different esters is called a crossed Claisen condensation. There are two main types of crossed Claisen that we will go over in this post. One is the reaction between esters, both having alpha hydrogens, and … Read more
Just like the aldol reaction, intramolecular Claisen reactions occur when five- or six-membered rings can be formed. These are called the Dieckmann condensation where one ester, of the same molecule, serves as an electrophile and the other is deprotonated and … Read more
We discussed quite extensively the aldol reactions of aldehydes and ketones, which involve enolate ions generated by base-catalysis. Esters are known to undergo an analog reaction called Claisen Condensation since they too have an acidic ɑ position to form an … Read more
In the previous post, we talked about the Michael reaction, which is a conjugate-addition reaction of doubly stabilized enolates such as malonic ester, acetoacetic ester, and the like with ɑ, β-unsaturated carbonyl compounds: One important variation of the … Read more
Michael reactions are conjugate-addition reactions of doubly stabilized enolates such as malonic ester, acetoacetic ester, and the like with ɑ, β-unsaturated carbonyl compounds: So, the Michael reaction is a particular type of conjugate addition reaction that ɑ, β-unsaturated … Read more
In the previous post, we talked about the acetoacetic ester synthesis, which is used for preparing ketones having one or two alkyl groups on the ɑ position: Another way to look at this reaction is to say that … Read more
The acetoacetic ester synthesis is a useful synthetic tool for preparing ketones having one or two alkyl groups on the ɑ position: At first, this may look confusing since there is a whole ester group being lost in … Read more
We have seen, in the alpha halogenation and aldol condensation reactions, that enolates are good nucleophiles capable of attacking halogens and carbonyl groups. In addition to these, enolates can also be alkylated when reacted with alkyl halides via the SN2 mechanism: … Read more
If a compound has two carbonyl groups (dicarbonyl compound), it undergoes an intramolecular aldol reaction if a five- or six-membered ring can be formed: What happens is one of the carbonyls is deprotonated at the ɑ position, thus … Read more
Carboxylic acids with α-hydrogen atoms can be brominated in the presence of catalytic amounts of phosphorus (or a phosphorus tribromide), forming α-bromo carboxylic acids. This is known as the Hell–Volhard–Zelinski (or HVZ) reaction: Now, let’s understand how this happens. First, … Read more
