SYNTHESIS OF FLUORINATED 1,2,3-BUTATRIENES FROM ALPHA-HALOVINYL ORGANOMETALLIC REAGENTS

The thermal stability and dimerization reaction of fluorinated alpha-h alovinyl zinc and copper reagents, RR'C=CYM (Y = F, Cl, Br; M = ZnX, C u), have been explored in detail. Dimerization of these vinyl carbenoi ds to butatrienes occurred when R was an aromatic (C6H5 or C6F5) and R ' was a perfluoroalkyl group (CF3, C2F5, C3F7). The role of the alpha- halogen was determined: the alpha-F vinyl copper reagent (R = C6H5, R' = CF3) decomposed by oxidative dimerization to 1,3-dienes while the a lpha-Br and -Cl copper reagents dimerized to butatrienes. The fluorina ted butatrienes prepared in this study, (E)- and (Z)-R1R2C=C=C=CR1R2 ( R1 = CF3, R2 = C6H5; R1 = C2F5, R2 = C6H5; R1 = n-C3F7, R2 = C6H5; R1 = CF3, R2 = C6F5) are available on a multigram scale and readily obtai ned with high isomeric purity. The geometry of one member of each isom eric pair of butatrienes was characterized by X-ray crystallography. T he mechanism of the dimerization reaction has been determined to be a nucleophilic displacement/beta-elimination process. Diels-Alder (1,2-a ddition), bromination (1,2-addition), and isomerization reactions are described.