Ketenes as privileged synthons in the syntheses of heterocyclic compounds part 2: Five-membered heterocycles

Ketenes are mostly used as the remarkable and common starting materials for structurally diverse five-membered and fused five-membered compounds, such as lactones, furans, benzofurans, dioxolane derivatives, pyrroles, succinimide, indoles, oxindoles, isoindoles, thiophenes, oxazoles, benzoxazoles, isoxazolols, oxathiolane derivatives, thiazoles, and thiadiazoles