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 alpha,beta -unsaturated carboxylic acids, althou gh a signal of 2 in F-19 NMR spectroscopy could be observed momentarily som etimes. However, the labile 2 can be trapped either with thiolate or phenox ide ions. The former reaction gives a mixture of CF2=CHCH(SR)R-1 and RSCF2C H=CHR1, whereas the latter affords only ArOCF2CH=CHR1. The nucleophilic sub stitution of the bromoanalogues, BrCF2CH,CHBrR1 and BrCF2CH=CHR1, has also been investigated. A mechanism involving S(N)2' and an allene intermediate is proposed. (C) 2001 Elsevier Science B.V. All rights reserved.