A ring forming reaction or ring-closing reaction in organic chemistry is a general term for a variety of reactions that introduce one or more rings into a molecule. A heterocycle forming reaction is such a reaction that introduces a new heterocycle.^[1][2] Important classes of ring forming reactions include annulations^[3] and cycloadditions.

Named ring forming reactions

Named ring forming reactions include (not exhaustive):

• Azide-alkyne Huisgen cycloaddition
• Bischler–Napieralski reaction
• Bucherer carbazole synthesis
• Danheiser annulation
• Dieckmann condensation
• Diels–Alder reaction
• Feist–Benary synthesis
• Fiesselmann thiophene synthesis
• Fischer indole synthesis
• Gewald reaction
• Hantzsch pyridine synthesis
• Larock indole synthesis
• Paal–Knorr synthesis
• Pictet–Spengler reaction
• Pomeranz–Fritsch reaction
• Ring-closing metathesis
• Robinson annulation
• Skraup reaction