Reaction of phIO·HBF4/silyl enol ether adduct with olefins as general approach to carbon—carbon bond formation in AdE reactions using hypervalent iodine reagents

Enolonium Species—Umpoled Enolates

“…[21] To circumvent this problem, an umber of elegant multistep alternatives have been developed. Reaction of the TMS enolate of propiophenone takes place to give the product in 50 %y ield (entry 8), which shows that the reaction is not limited to enolates of methyl ketones.I mpressively,t he reaction works well for reverse prenylation of ketone enolates (Table 2 entries [14][15][16][17][18][19][20], as well as for cinnamylation (entry 21) and crotylation (entry 9-13). Reaction of the TMS enolate of propiophenone takes place to give the product in 50 %y ield (entry 8), which shows that the reaction is not limited to enolates of methyl ketones.I mpressively,t he reaction works well for reverse prenylation of ketone enolates (Table 2 entries [14][15][16][17][18][19][20], as well as for cinnamylation (entry 21) and crotylation (entry 9-13).…”

“…Communications to single-step formation of products of 21 and 24-42 in 40-92 %y ields ( Table 2). Reaction of the TMS enolate of propiophenone takes place to give the product in 50 %y ield (entry 8), which shows that the reaction is not limited to enolates of methyl ketones.I mpressively,t he reaction works well for reverse prenylation of ketone enolates (Table 2 entries [14][15][16][17][18][19][20], as well as for cinnamylation (entry 21) and crotylation (entry 9-13). These results,a nd the reaction of propiophenone (entry 8), show the potential for developing asymmetric applications of this chemistry.P otentially oxidizable iodide (entries 4a nd 17) and alkene functionalities (entries 6, 12 and 19) are also compatible with these conditions.…”

“…If the hypervalent iodine 3 possesses agood leaving group X or if a b-keto-ester were used as the substrate,i odonium ylides 7 might result. [19] Immediate addition of alkenes to the reaction led to alkenylated products in 10-90 %y ields.T he reaction with allylsilane 20 gave allylated ketone 21 in 62 %yield. [20] We therefore decided to focus on enolates of methyl ketones.…”

“…Theinspiration was areport by Zhdankin et al that the TMS enolether 8 of acetophenone could be made to react with iodosylbenzene (9)a ctivated by HBF 4 to give an unidentified electrophilic species in solution at low temperature. [19] Immediate addition of alkenes to the reaction led to alkenylated products in 10-90 %y ields.T he reaction with allylsilane 20 gave allylated ketone 21 in 62 %yield. Surprisingly,this interesting finding has gone largely unused.…”

Tetrafluoroboric Acid

“…Preparation of a Useful Hypervalent Iodine Reagent.When treated with HBF 4 ·OMe 2 at low temperatures, Iodosylbenzene reacts with silyl enol ethers to form a hypervalent iodine adduct capable of useful carbon-carbon bond formation reactions with alkenes (eq 14) 32. …”