Investigation of bis(tributyltin)-initiated free radical cyclization reactions of 4-pentenyl iodoacetates.
Bis(tributyltin)-initiated atom transfer cyclization reactions of 4-pentenyl iodoacetates (1) at 80 degrees C led to the formations of 5-(3-iodopropyl)-substituted dihydro-2(3H)-furanones (3) in high yield. With BF3*Et2O as the catalyst, the reactions were run at room temperature to afford the corresponding gamma-iodoheptanolactones (2), which could be further transformed into 3-(tetrahydro-2-furyl)propanoic acids (6) upon treatment with aqueous NaHCO3. The reaction mechanism was postulated to be the 8-endo free radical cyclization to generate gamma-iodoheptanolactones which easily underwent intramolecular nucleophilic substitution to form bicyclic acylium species (7) as the key intermediate. Subsequent attack by iodide ion furnished gamma-lactones while attack by hydroxide ion gave the tetrahydrofuran derivatives.
Wang
Junhua
J
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, PR China.
Li
Chaozhong
C