Lactam
Cyclic amide
A lactam is a cyclic amide, formally derived from an amino carboxylic acid through cyclization reactions. The term is a portmanteau of the words lactone + amide.
01Nomenclature
Greek prefixes in alphabetical order indicate ring size.
| Ring size (number of atoms in the ring) |
Systematic name | IUPAC name | Common name(s) | Structure |
|---|---|---|---|---|
| 3 | α-Lactam | Aziridin-2-one | α-Acetolactam | |
| 4 | β-Lactam | Azetidin-2-one | β-Propiolactam | |
| 5 | γ-Lactam | Pyrrolidin-2-one |
|
|
| 6 | δ-Lactam | Piperidin-2-one |
|
|
| 7 | ε-Lactam | Azepan-2-one |
|
This ring-size nomenclature stems from the fact that hydrolysis of an α-lactam gives an α-amino acid and that of a β-Lactam gives a β-amino acid, and so on.
02Synthesis
General synthetic methods are used for the organic synthesis of lactams.
Beckmann rearrangement
Lactams form by the acid-catalyzed rearrangement of oximes in the Beckmann rearrangement.
Schmidt reaction
Lactams form from cyclic ketones and hydrazoic acid in the Schmidt reaction. Cyclohexanone with hydrazoic acid, forms ε - Caprolactam, which upon treatment with excess acid forms Cardiazole, a heart stimulant.
Cyclization of amino acids
Lactams can be formed from cyclisation of amino acids via the coupling between an amine and a carboxylic acid within the same molecule. Lactamization is most efficient in this way if the product is a γ-lactam. For example, Fmoc-Dab(Mtt)-OH, although its side-chain amine is sterically protected by extremely bulky 4-Methyltrityl (Mtt) group, the amine can still intramolecularly couple with the carboxylic acid to form a γ-lactam. This reaction almost finished within 5 minutes with many coupling reagents (e.g. HATU and PyAOP).
Intramolecular nucleophilic substitution
Lactams form from intramolecular attack of linear acyl derivatives from the nucleophilic abstraction reaction.
Iodolactamization
An iminium ion reacts with a halonium ion formed in situ by reaction of an alkene with iodine.
Kinugasa reaction
Lactams form by copper-catalyzed 1,3-dipolar cycloaddition of alkynes and nitrones in the Kinugasa reaction
Diels-Alder reaction
Diels-Alder reaction between cyclopentadiene and chlorosulfonyl isocyanate (CSI) can be utilized to obtain both β- as well as γ-lactam. At lower temp (−78 °C), β-lactam is the preferred product. At optimum temperatures, a highly useful γ-lactam known as Vince Lactam is obtained.
03Lactam-lactim tautomerism
A lactim is a cyclic imidic acid compound characterized by an endocyclic carbon-nitrogen double bond. They are formed when lactams undergo tautomerization.
Sources and credits
This article is adapted from the Wikipedia article “Lactam”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Lactams.svg by User:Innerstream, Public domain
- Lactam-Lactim-Tautomerie.svg by NEUROtiker (talk), Public domain
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