Convenient and Highly Efficient Routes to 2 H-Chromene and 4-Chromanone Derivatives: Iodine-Promoted and p-Toluenesulfonic Acid Catalyzed Cascade Cyclizations of Propynols

A convenient strategy is presented for the easy preparation of a series of 2 H‐chromenes under mild conditions through iodocyclization of readily accessible propynols. In addition, various 4‐chromanones can be synthesized through a p‐toluenesulfonic acid catalyzed cascade cyclization with high efficiency (yields up to 99 %). Our developed reaction systems are proven to have good functional‐group applicability and can be scaled up to gram quantities in satisfactory yields. These systems also provide a new synthetic strategy for two types of important flavonoid skeleton without using costly and toxic metal catalysts. Additionally, the resulting halides could be further exploited in subsequent palladium‐catalyzed coupling reactions, so these compounds could act as potential intermediates for the construction of some valuable drug molecules. A better route: Convenient and highly efficient strategies are presented for the easy preparation of 2 H‐chromenes and 4‐chromanones through iodocyclization and p‐toluenesulfonic acid (p‐TsOH) catalyzed cascade cyclization of readily accessible propynols (see scheme). The developed systems have good functional‐group applicability, can be scaled up to gram quantities in satisfactory yields, and provide a new synthetic strategy for two types of important flavonoid skeleton without using costly and toxic metal catalysts.