Lactam

From left to right, general structures of a β-lactam, a γ-lactam, a δ-lactam and a ε-lactam.

A lactam (the noun is a portmanteau of the words lactone + amide) is a cyclic amide. Prefixes indicate how many carbon atoms (apart from the carbonyl moiety) are present in the ring: β-lactam (2 carbon atoms outside the carbonyl, 4 ring atoms in total), γ-lactam (3 and 5 total), δ-lactam (4 and 6 total). Beta β, gamma γ and delta δ are the second, third and fourth letters in the alphabetical order of the Greek alphabet, respectively.

Synthesis

General synthetic methods exist for the organic synthesis of lactams.

• Lactams form by the acid-catalyzed rearrangement of oximes in the Beckmann rearrangement.
• Lactams form from cyclic ketones and hydrazoic acid in the Schmidt reaction.
• Lactams form from cyclisation of amino acids.
• Lactams form from intramolecular attack of linear acyl derivatives from the nucleophilic abstraction reaction.
• In iodolactamization an iminium ion reacts with an halonium ion formed in situ by reaction of an alkene with iodine.

• Lactams form by copper catalyzed 1,3-dipolar cycloaddition of alkynes and nitrones in the Kinugasa 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.

Tautomerization to Lactim

Lactim is a cyclic carboximidic acid compound characterized by an endocyclic carbon-nitrogen double bond. It is formed when lactam undergoes tautomerization.

Reactions

• Lactams can polymerize to polyamides.

See also

• β-lactam with a four-membered ring found in beta-lactam antibiotics. Penicillin, considered the most famous antibiotic, is a β-lactam antibiotic.
• Lactone, a cyclic ester.
• Caprolactam