A free radical synthesis of Y-lactones using tri-n-butylstannyl iodoesters
Interest in the use of free radical reactions in synthetic organic chemistry has greatly intensified in recent years. A program was undertaken to develop a free radical synthesis of (gamma)-lactones which would occur under neutral conditions. Thus, treatment of olefins with tri-n-butylstannyl iodoacetate in the presence of a catalytic amount of the free radical initiator, 2,2'-azobis(2-methylpropionitrile) (AIBN) in refluxing benzene resulted in good yields of 4-substituted-(gamma)-lactones. The products were separated from iodotri-n-butylstannane by partitioning between acetonitrile and hexanes. Further purification by column chromatography afforded the pure (gamma)-lactones;This reaction has also been extended to the synthesis of bicyclic lactones via the intramolecular cyclizations of appropriately constructed tri-n-butylstannyl iodoesters under the same reaction conditions. The mild reaction conditions employed allow for the introduction of a variety of functional groups at the 4-position including alcohols, ethers, and even alkylsilanes and silyl ethers.