Nitrogensyklene

Nitrogensyklene are nitrogen-containing cyclic compounds in which a nitrogen atom is part of a ring that also contains one or more carbon–carbon double bonds. In chemistry literature they are often described as azacycloalkenes. The term covers a range of structures, typically five- to seven-membered rings, in which the ring contains at least one C=C bond and one nitrogen atom. The nitrogen can participate as a secondary amine in non-conjugated rings or as part of an imine- or enamine-like system when the double bonds are conjugated with the nitrogen.

Structurally, nitrogensyklene encompass several classes of azacycles, including five-membered rings such as dihydropyrroles (pyrroline) and related unsaturated azacycles, as well as six- and seven-membered rings such as azacyclohexenes, azacycloheptenes, and azepines in various unsaturated forms. The exact electronic character of the ring nitrogen depends on the degree of conjugation with the adjacent double bonds, influencing properties such as basicity and nucleophilicity.

Synthesis of nitrogensyklene commonly involves ring-closing strategies to form the heterocycle, including cyclization of aminoalkenes, intramolecular nucleophilic additions, and ring-closing metathesis, as well as dehydrogenation of saturated azacycles. Their reactivity is governed by ring strain and conjugation; the lone pair on nitrogen may be part of the π-system in conjugated examples, reducing basicity, while non-conjugated variants can behave more like typical amines.

Applications and significance arise from their presence in natural products and medicinal chemistry, as intermediates in organic synthesis, and as motifs with distinct electronic properties relevant to materials and catalysis. See also azacycles, heterocycles, and azacycloalkenes.