Iododifluoromethyl alkenes [ICF2CHCHR]: a labile system generated from 1,1-difluoro-1,3-diiodoalkanes and its trapping with nucleophiles

Treatment of 1,1-difluoro-1,3-diiodoalkanes (ICF2CH2CHIR1, 1) with NEt3 in various solvents or with KF/Al2O3/CH3CN gave no alkenes (ICF2CHCHR1, 2), whereas with NaOH afforded α,β-unsaturated carboxylic acids, although a signal of 2 in 19F NMR spectroscopy could be observed momentarily sometimes. However, the labile 2 can be trapped either with thiolate or phenoxide ions. The former reaction gives a mixture of CF2CHCH(SR)R1 and RSCF2CHCHR1, whereas the latter affords only ArOCF2CHCHR1. The nucleophilic substitution of the bromoanalogues, BrCF2CH2CHBrR1 and BrCF2CHCHR1, has also been investigated. A mechanism involving SN2′ and an allene intermediate is proposed.