Intramolecular Cascade Lactone Cyclization of Dicoumarol Derivatives Promoted by Tributyltin Chloride

Dicoumarols, derived from aldehydes with ortho hydroxy substitution (5 and 7), were successfully cyclized by Sn(n-Bu)3Cl in THF as a reaction medium. Catalytic cycle reveals the formation of HO-Sn-O=C cyclic intermediate which is rearranged and isomerized to the cyclic lactone. N-butane was released by Sn(n-Bu)3Cl leaving behind Sn(n- Bu)2(OH)Cl keeping the catalytic route continued unless the two butane attached to tin were also consumed. The products produced were characterized using 1H, 13C{1H}-NMR, high resolution EI-MS, IR and elemental analyses. Single crystals of 6 were grown in P1 space group from concentration in THF and structurally studied using X-ray diffraction analysis. All the spectroscopic and analytical studies supported the formation of the cyclized products.