Pd(II)-Catalyzed Dehydrogenative Olefination of Vinylic C–H Bonds with Allylic Esters: General and Selective Access to Linear 1,3-Butadienes

Abstract

This work demonstrates a general and efficient method to prepare conjugated dienes by Pd(II)-catalyzed direct olefination of unactivated alkenes with allylic esters and acrylates via vinylic C-H activation. Various aryl and heteroaryl alkenes as well as aliphatic alkenes all give the desired linear 1,3-butadienes with retention of the traditional leaving groups such as OAc and other carboxylic acid ester groups.

Palladium‐Catalyzed Oxidative Cross‐Coupling of α‐Cyanoketene Dithioacetals with Olefins

“…Loweringt he catalyst loading to 10 mol %s lowed down the reactiona nd as atisfactory yield was only reached over ap eriod of 30 h( Ta ble 1, entry 2). Dioxane, HOAc, DMSO,o ramixture of dioxane and HOAc (3:1 v/v) as the solventd iminished the reaction efficiency ( Table 1, entries 3-6), whereas an acidic mixture of dioxane,H OAc, and DMSO (9:3:1 v/v/v) [8a] as the medium promoted the reaction to completion within 3h,f urnishing 3a in 95 %y ield (isolated product) without occurrenceo ft he homocoupling of 1a ( [12][13][14][15][16], giving yields comparable to those obtained by using AgOAc as the terminal oxidant within 7h.T he ability of molecular dioxygen to effect the facile oxidation of Pd 0 speciesi nt he catalytic cycle is ascribed to the presenceo fD MSO in the reaction mediium,w hich acts as al igand with both hard (O-)a nd soft (S-)d onor atoms and facilitates the redox cycling between palladium(II)and palladium(0)inthe reaction. [18] Thus, the reaction conditions were optimized as those for Ta ble 1, entry 15: Pd(OAc) 2 (10 mol %) as the catalyst, dioxane/HOAc/DMSO (9:3:1 v/v/v)a st he solvent, air (balloon), T = 50 8C, and t = 7h.…”

“…[11e] Liu andc o-workersr ealized palladium-catalyzed oxidative vinylicC ÀHo lefination with allylic esters. [12] To improvet he olefination efficiencyo fv inylogous CÀHb onds with olefins, the groups of Loh and Glorius both introduced ad irecting group to one of the olefin substrates to enables elective oxidative cross-coupling between two terminal olefins, achieving CÀHo lefination of enamides, [13a, 14a] acrylamides, [13b] and carbonyl-bearing olefins [14b] with different olefin partners. However, in most of the above-mentionedc ases, the oxidative cross-coupling occurred between two terminal olefins, suggesting that olefination of internal vinylogousC ÀHb onds is very challenging.…”

“…Later, Loh and co‐workers documented palladium‐catalyzed oxidative CH olefination of acrylates,11a–c and vinyl ketones11d with simple olefins, and ruthenium‐catalyzed oxidative stereo‐ and chemoselective cross‐coupling between two electron‐deficient acrylates 11e. Liu and co‐workers realized palladium‐catalyzed oxidative vinylic CH olefination with allylic esters 12. To improve the olefination efficiency of vinylogous CH bonds with olefins, the groups of Loh and Glorius both introduced a directing group to one of the olefin substrates to enable selective oxidative cross‐coupling between two terminal olefins, achieving CH olefination of enamides,13a, 14a acrylamides,13b and carbonyl‐bearing olefins14b with different olefin partners.…”

Stereoselective Construction of (E,Z)‐1,3‐Dienes and Its Application in Natural Product Synthesis

“…Thus, engaging simple, terminal olefins in transition‐metal‐catalysed C−H bond activation might provide a more direct and atom‐economic approach towards conjugated dienes. Following the seminal work on Pd‐catalysed oxidative cross‐coupling of specific terminal olefins by Ishii, [89] Loh, [90] Yu, [91] and Liu, [92] the direct Rh‐ or Ru‐catalysed oxidative olefination of vinylic C−H bonds has been developed by using directing groups (Scheme 36). Such methodology is beneficial due to its high selectivity for linear products over branched ones, mono‐olefination, and Z ‐configurations.…”

Facile Preparation of (2<em>Z</em>,4<em>E</em>)-Dienamides by the Olefination of Electron-deficient Alkenes with Allyl Acetate

“…Recently, direct cross-couplings between two alkenes via double vinylic C-H bond activation was developed, representing an efficient strategy for the synthesis of butadienes, with high atomic and step economy. Among them, the palladium-catalyzed cross-coupling of two alkenes has attracted much attention, providing (E,E)-configured butadienes via alkenyl-Pd species 4,5 . For example, Liu's group developed a Pd-catalyzed butadiene synthesis by the direct cross-coupling of alkenes and allyl acetate (Figure 1 and Equation 3)…”