Highly strained unsaturated carbocycles

Highly strained unsaturated carbocyclic rings are high-energy compounds which are attracting increasing interest \u2013 not just for their peculiar structural and reactivity features \u2013 but also as modern chemical tools for bioorthogonal and in vivo chemistry, especially via inverse-electron demand Diels\u2013Alder (iEDDA) and strain-promoted azide-alkyne cycloaddition (SPAAC) reactions. This mini-review covers two main classes of compounds: 3 to 10 membered-ring cycloalkynes and trans-cycloalkenes, including some examples of cyclic enynes, dienes and bridgehead alkenes. Their molecular properties, synthesis and reactivity are presented and discussed, with an emphasis on their functionalization and reactivity