Acid-Catalyzed, Three-Component, Spontaneous Cascades of 1,3-Butadiynyl Propargylic Alcohols as a Route to Phthalan Derivatives

We have established an ambient temperature, one-pot, acid-catalyzed, three-component process involving in situ formation of a tetrayne or triyne that spontaneously cyclizes to a benzyne intermediate. This was rapidly captured to give a diverse range of polycyclic phthalan derivatives. Product structural diversity was enhanced by employing various combinations of alkyne substrates and benzyne trapping reagents. This cascade reaction was versatile and efficient and could be effected by a variety of Lewis and Brønsted acid catalysts. Success in an aqueous or even a solvent-free environment was demonstrated.