Radical addition of RFI to alkenylsuccinic anhydrides and gem-substituted alkenyl triesters: Zinc and radical induced, or spontaneous radical cyclization, of the δ-iodoalkanoic esters to γ-lactones

Radical addition of RFI to alkenylsuccinic anhydrides affords ω-(perfluoroalkyl)-δ-iodoalkyl-2-butane-1,4-dioc acid anhydrides, and these adducts are reductively dehalogenated and esterified by zinc and acid in ethanol without lactonization. However, the RFI adducts react with KOH in ethanol to give the alkenyl half esters (but no γ-lactone), which convert to the γ-lactones by acid catalysis. When treated with water, ethanol, Zn and 48% HBr, the RFI adduct from but-3-en-2-yl-succinic anhydride converts to the iodo half ester, RFCH2CHICH(CH3)CH(CO2H)CH2CO2Et, which undergoes Zn induced (SHi) conversion to γ-lactone. RFI (AIBN) and the triester CH2CHCH2C(CO2Et)2CH2CO2Et yield RFCH2CHICH2C(CO2Et)2CH2CO2Et (95%). When heated to 140 °C, the adduct loses iodoethane.and cyclizes to diester γ-lactones (94%). With benzoyl peroxide, RFI and the triester at 99 °C, spontaneous radical cyclization of the adduct to lactone occurs. Evidently, the gem-disubstituted triester readily forms a five-membered lactone as a consequence of steric compression in the open chain form.