Selective Cα-O bond cleavage of chalcone epoxides induced by pyrylium salt sensitized photoreactions and dark reactions with cerium(iv) salts

Photosonochemical catalytic ring opening of α-epoxyketones

“…These reactions have been observed thermally by ceric ammonium nitrate (CAN), [28,29] 2,3-dichloro-5,6-dicyano- p -benzoquinone (DDQ) [30] and iron(III) chloride [31] or photo-induced electron transfer reactions by dicyanoanthracene (DCA), [32,33] tetracyanoethylene (TCNE) [34,35] and 2,4,6-triphenylpyrilium tetrafluoroborate. [36-40] In the case of C-C bond cleavage, the generated intermediates from epoxide radical cations have been trapped by molecular oxygen to form trioxolane derivatives [32-34] or by dipolarophiles to form various tetrahydrofurans and dihydrofurans. [41] In the absence of appropriate dipolarophiles, cis / trans isomerization of the epoxide ring has been observed.…”

“…[42] The cleavage of C α -O or C β -O bonds has been confirmed either by rearrangement to carbonyl compounds [43-50] or by nucleophilic attack of appropriate reagents. [36,39,51]…”

Photocatalytic Acetolysis of α‐Epoxyketones

“…[1][2][3][4][5] In re cent years ther mal and pho to chem i cal ring opening of these com pounds in the pres ence of var i ous nucleophiles stim u lated by elec tron trans fer to suit able cat a lysts or photocatalysts has been stud ied in ten sively. 25 Photocatalytic ring open ing of epoxides and -epoxyketones by the use of dicyanoanthracene, 7 tetracyano ethylene, 8,18 and 2,4,6-triphenylpyrylium tetrafluoroborate 10 as photocatalyst has been re ported. 25 Photocatalytic ring open ing of epoxides and -epoxyketones by the use of dicyanoanthracene, 7 tetracyano ethylene, 8,18 and 2,4,6-triphenylpyrylium tetrafluoroborate 10 as photocatalyst has been re ported.…”

“…[6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] Sin gle electron trans fer (SET) in duced ring open ing of epoxides has been re ported ther mally in the pres ence of var i ous elec tron ac cep tors such as ceric am mo nium ni trate, 11,13,17 2,3-di chloro-5,6-dicyano-p-benzoquinone, 9 iron(III) chlo ride, 15 tristrinitrato Ce(IV) paraperiodate (TTCPP), 16 FeCl3*6H2O sup ported on SiO2, 19 ceric tetraflate 22 and bis muth(III) chloride. In all of these re ac tions, three dif fer ent ring open ings through C-C, C -O and C -O bond cleav ages have been ob served, whereas C-O bond cleav age fol lowed by nucleophilic at tack of wa ter, al co hols, carboxylic ac ids or ac e tone re sulted in the for ma tion of glycols, 13,19,[22][23][24][25] alkoxy al co hols, 6,[9][10][11]15,19,[22][23][24][25] hydroxyester de riv a tives 13,19,20,…”

ElectronTransfer Induced Ring Opening of α-Epoxyketones: Spirodioxolane Formation

“…Single electron transfer (SET) induced ring opening reactions of epoxides [ 1 , 2 , 3 , 4 ], α-epoxyketones [ 5 , 6 , 7 , 8 ] and α-epoxyesters [ 9 ] have demonstrated C α -C β , C α -O and C β -O bond cleavage through photosensitized electron transfer by dicyanoanthracene [ 1 , 2 ], tetracyanoethylene [ 3 , 4 ] and 2,4,6-triphenylpyrylium tetrafluoroborate [ 5 , 6 , 7 , 8 ] or thermally induced electron transfer to ceric ammonium nitrate [ 10 , 11 ], 2,3-dichloro-5,6-dicyano- p -benzoquinone [ 12 ] and iron (III) chloride [ 13 ].…”