Gold‐Catalyzed Heterogeneous Aerobic Dehydrogenative Amination of α,β‐Unsaturated Aldehydes to Enaminals

Abstract

Although enaminals (β‐enaminals) are very important compounds and have been utilized as useful synthons for various important compounds, they have been synthesized through non‐green and/or limited procedures until now. Herein, we have successfully developed a green synthetic procedure using a heterogeneous catalyst. In the presence of gold nanoparticles supported on manganese‐oxide‐based octahedral molecular sieves OMS‐2 (Au/OMS‐2), dehydrogenative amination of α,β‐unsaturated aldehydes with amines proceeded efficiently, with the corresponding enaminals isolated in moderate to high yields (50–97 %). The catalysis was truly heterogeneous, and Au/OMS‐2 could be reused. Furthermore, the formal Wacker‐type oxidation of α,β‐unsaturated aldehydes to enaminones has been realized.

Supported Gold Nanoparticles for Efficient α‐Oxygenation of Secondary and Tertiary Amines into Amides

“…A cyclic tertiary amine with an alcohol group reacted well, and the hydroxy group in 2p remained intact (Table 2, entry 4). Methylvinylketone [21] and ethylacrylate could also be applied to the sequential reaction (Scheme 2b and 2c). Cloperastine,acough suppressant, [19] was also selectively oxygenated to give the corresponding amide,l eaving chloride and ether functional groups intact (Table 2, entry 6).…”

“…[20] Furthermore,w es uccessfully synthesized 2t starting from 1a and acrylonitrile through an aza-Michael addition/ a-oxygenation one-pot sequential reaction (Scheme 2a). Methylvinylketone [21] and ethylacrylate could also be applied to the sequential reaction (Scheme 2b and 2c).…”

Gold Nanoparticles Supported on a Layered Double Hydroxide as Efficient Catalysts for the One‐Pot Synthesis of Flavones

“…[7] Thep resent one-pot process consists of aC laisen-Schmidt condensation (base catalysis), an intramolecular oxa-Michael addition (base catalysis), and an aerobic oxidative dehydrogenation of chromanones (gold catalysis;r oute Bi n Scheme 1). [8][9][10] When benzyl alcohols are used as the starting materials,t he sequence begins with aerobic oxidation of the alcohol (gold catalysis). [7] TheA u/LDH catalyst plays multiple roles in this process,c atalyzing all the different types of reactions included in this sequence.T he catalysis is shown to be truly heterogeneous,a nd the Au/LDH catalyst can be reused without as evere loss of catalytic performance.T he present procedure possesses several noteworthy features,for example,1 )the use of ar eusable heterogeneous catalyst, 2) simple one-pot operation and avoidance of tedious isolation steps,3 )the use of the greenest oxidant, namely molecular oxygen (in air), as the terminal oxidant, 4) readily available starting materials,5 )non eed for additives,a nd 6) the formation of water as the theoretically only by-product.…”