A New Reaction for Organoselenium Compounds: Alkyl Transfer from Diorganoselenium(IV) Dibromides to Alkenoic Acids To Give γ- and δ-Lactones

Various 1-[[bis(1-methylethyl)amino]carbonyl]-2-(dibromo-n-alkylseleno) ferrocene derivatives reacted with 2 equiv of 4-pentenoic acid or 5-hexenoic acid to give the corresponding γ-or δ-lactones, respectively, from transfer of the alkyl group bound to selenium to the terminal alkene carbon. In the lactone cyclization, 1-[[bis(1-methylethyl)amino]carbonyl]-2- (bromoselenenyl)ferrocene (25) is formed and reacts with a second equivalent of the alkenoic acid to give either 5-[1-[[bis(1-methylethyl)amino]carbonyl] ferrocene-2-selenenylmethyl]tetrahydro-2-furanone (23) or 6-[1-[[bis(1- methylethyl)amino]carbonyl]ferrocene-2-selenenylmethyl]tetrahydro-2 H-pyran-2-one (26) as a mixture of diastereomers in yields comparable to the corresponding γ-or δ-lactone. The addition of 1-[[bis(1-methylethyl) amino]carbonyl]-2-(dibromo-n-butylseleno)ferrocene to 3-butenoic acid gave alkyl transfer to the internal alkene carbon and formation of the γ-lactone. Density functional theory (DFT) geometry optimizations were performed on several idealized n-alkyldibromselenoferrocene structures to examine the role of iron in the alkyl transfer and the role of various structural features on the alkyl carbon - selenium bond length. The results of the computations suggested that the ferrocenyl iron was not involved in the alkyl transfer reactions.