Ultrasound-promoted synthesis of .alpha.-difluoromethylated carboxylic acids

Convenient synthesis of fluorinated alkanes and cycloalkanes by hydrogenation of perfluoroalkylalkenes under ultrasound irradiation

“…The authors concluded that sonication of the reaction mixture accelerates the reaction as if it was at reflux [13]. This is similar to the observations of Kitazume et al [14]. They described the first hydrogenation of difluorinated acrylic acids or their benzyl esters which did not proceed under normal conditions.…”

“…We also observed a higher reaction rate when the alkene bears a perfluoroalkyl group rather than two fluorine atoms ( Table 2, entry 17). Most of our reactions were complete within 6 h which is five-fold faster than Kitazume's reactions [14] which is surprising: for two fluorine atoms directly linked to a double bond, the mesomeric donor effect should be more important than the inductive attractor effect. Basically catalytic hydrogenation rate is only slightly enhanced by the electronic effects and much more affected by the bulkiness of molecule [5].…”

An efficient stereoselective synthesis of difluoromethylated alkenes in a microreactor

“…Furthermore, difluoromethyl substitution on an organic molecule often confers bioactivity on these compounds and can serve as a diagnostic handle for functionalized materials [6]. To date, we have reported the synthetic routes for difluoromethyl compounds derived from terminal difluoro olefins by hydrogenation using a 10% palladium on carbon catalyst [7] and difluoroacetaldehyde ethyl hemiacetal [8].…”

The effect of fluoromethyl groups on the diastereoselectivity in the electrophilic alkylation

“…1 H NMR (CDCl 3 ): d 5.21 (2H, s), 6.18 (1H, ddt, J = 1. 20,4.05,54.92 Hz),6.30 (1H,dtd,J = 0.90,3.00,15.90 Hz),6.83 (1H,dtd,J = 4.20,10.20,15.90 Hz),m). 13 C NMR (CDCl 3 ) : d 66.88,112.20 (t,J = 236.73 Hz),126.77 (t,J = 10.57 Hz),128.11,128.26,128.38,134.99,136.59 (t,J = 24.07 Hz), 164.08.…”

“…These compounds were prepared from the corresponding crotonates 8a or 8b in the same procedure by hydrolysis [19], chlorination [20] and condensation. These yields were isolated yield in the condensation step.…”