Development of highly efficient platinum catalysts for hydroalkoxylation and hydroamination of unactivated alkenes

Abstract

Hydrofunctionalization, the direct addition of an X–H (e.g., X=O, N) bond across an alkene, is a desirable strategy to make heterocycles that are important structural components of naturally occurring molecules. Described here is the design and discovery of “donor–acceptor”-type platinum catalysts that are highly effective in both hydroalkoxylation and hydroamination of unactivated alkenes over a broad range of substrates under mild conditions. A number of alkene substitution patterns are accommodated, including tri-substituted, 1,1-disubstituted, (E)-disubstituted, (Z)-disubstituted and even mono-substituted double bonds. Detailed mechanistic investigations suggest a plausible pathway that includes an unexpected dissociation/re-association of the electron-deficient ligand to form an alkene-bound “donor–acceptor”-type intermediate. These mechanistic studies help understand the origins of the high reactivity exhibited by the catalytic system, and provide a foundation for the rational design of chiral catalysts towards asymmetric hydrofunctionalization reactions.

Reagent-free intramolecular hydrofunctionalization: a regioselective 6-endo-dig cyclization of o-alkynoylphenols

“…bonds across alkenes and alkynes. [5][6][7] Intramolecular hydrofunctionalization reactions such as hydroalkoxylation and hydroamination are expedient and stepand atom-economical approaches for the construction of heterocycles. 8,9 In this regard, numerous catalytic hydrofunctionalizations of alkynes have emerged as convenient methods to access a wide variety of functionalized heterocycles with high levels of efficiency and regioselectivity in the last few years.…”

“…11 The intramolecular hydrofunctionalizations of alkynes are catalyzed by transition metal and inner transition metal complexes, which primarily activate electrophiles such as alkynes or nucleophiles such as the O-H or N-H group (Scheme 1A and B). 6,10,[12][13][14] Besides, a few metal-free synthetic methods for acid-or base-catalyzed reactions have been studied, particularly for the intramolecular alkoxylation of o-alkynoylphenols (Scheme 1C). 8,[15][16][17][18][19] The alkoxylation might be achieved owing to the presence of both the reactive carbonyl and the polarized α,β-alkyne moieties (i.e., ynones).…”

Catalytic Asymmetric Hydroalkoxylation of C–C Multiple Bonds

“…In another report showcasing the ability of platinum to activate C–C double bonds, Xu and co-workers recently described a platinum(II)-catalyzed intramolecular hydroalkoxylation of alkenes ( Scheme 19 ). 82 The author’s approach relies on the design a of “donor–acceptor” type bifunctional Pt(II)-catalyst, where the monodentate phosphine ligand contains a basic imidazole unit that can engage in hydrogen bonding with the nucleophilic alcohol to form a well-defined TS 27 . Thus, with additional aid of a Thorpe–Ingold effect in the substrate, a chiral tetrahydrofuran was obtained in moderate yield, albeit with poor enantioselectivity.…”

Hydrothermal Synthesis of Biomass-Derived Magnetic Carbon Composites for Adsorption and Catalysis

“…Fe/C contributes to this, the presence of iron in Fe/C enhances catalytic activity via electrophilic bonding to the alkyne. 78 There is then likely a synergistic interaction between iron and carbon, whereby the hydrochar facilitates hydroalkoxylation through stabilizing the hydroxide group, resulting in the formation of the stabilized enol transition state. 78,79 These studies demonstrate the potential to synthesize active and selective catalytic materials from low-value waste and co-product streams via HTC.…”