Synthesis and heck reactions of ethenyl- and (Z)-butadien-1-yl nonaflate obtained by the fragmentation of furan derivatives

The nonaflation of lithium enolates or of silyl enol ethers, formally deriv ed from acetaldehyde or crotonaldehyde, with nonafluorobutanesulfonyl fluor ide gave ethenyl nonaflate (lb) and (Z)-buta-1,3-dien-1-yl nonaflate (2) in good yields. The required enolates were obtained by aldehyde-free routes b y the lithiation of tetrahydrofuran or 2,5-dihydrofuran followed by the cyc lofragmentation of the metallated heterocycles. The application of this app roach to the synthesis of allenyl nonaflate 3 failed, presumably due to the intrinsic instability of this allene derivative, The nonaflates lb and 2 w ere also prepared by the fluoride-catalysed reaction of the corresponding s ilyl enol ethers 5 and 7 with nonafluorobutanesulfonyl fluoride; however, t he overall yields are slightly lower for these two-step pathways. The cyclo fragmentation of lithiated 2,2-dimethyl-4-methylene-[1,3]dioxolane allowed the easy preparation of trimethylsiloxyallene (10) in moderate yield. The n onaflates lb and 2 reacted smoothly with monosubstituted alkenes in the pre sence of a catalytic amount of palladium(II) acetate to give the anticipate d Heck coupling products in good to moderate yields and with high stereosel ectivities.