Catalytic Oxidation of Alkynes into 1,2‐Diketone Derivatives by Using a Pd^II/Lewis‐Acid Catalyst

Abstract

An ew synthetic methodh as been developed for the efficient oxidation of alkynesi nto 1,2-diketones by using aP d II /Lewis acid catalytic system using DMSO as the oxidant and solvent. Under our optimized reactionc onditions, this approach tolerated avariety of functional groups and afforded 1,2-diketone derivatives in 62

Pd(ii)/Lewis acid catalyzed regioselective olefination of indole with dioxygen

“…6–8,28,43–46 Herein, adding Cu(OAc) 2 instead of Cu(OTf) 2 to Pd(OAc) 2 as the catalyst provided only 35% yield of 3a , much less than that (75%) obtained by adding Sc(OTf) 3 , highlighting the significant role of the Lewis acid properties of the added non-redox metal ions in this Pd( ii )/LA catalysis as well as in our previous studies. 11–19 In addition, adding HOTf instead of Sc(OTf) 3 to Pd(OAc) 2 as the catalyst gave only 11% yield of 3a , and using Pd(OTf) 2 directly as the catalyst did not provide the olefination product, however plenty of palladium black was formed (Table 1, entries 13 and 14). In the control experiments without Pd(OAc) 2 , Lewis acids such as Sc(OTf) 3 alone could not catalyze this reaction (Table 1, entry 15).…”

“…The active Pd( ii )/Sc( iii ) catalyst existed as a diacetate bridged heterobimetallic Pd( ii )/Sc( iii ) cluster, as shown in previous studies. 10–17 The linkage of the Sc 3+ cation to the Pd( ii ) species through the acetate bridge enhanced its electrophilic properties, thus improving its catalytic efficiency. Apparently, a stronger Lewis acid may provide a better enhancement of the electrophilic properties of the Pd( ii ) species, thus offering a higher promotional effect in this Pd( ii )/LA catalyzed indole olefination reaction, as shown in Table 1.…”

“…So far, this Pd( ii )/LA catalysis has been applied in olefin oxidation and isomerization, benzene hydroxylation, alkyne oxidation, nitrile hydration, the olefination/annulation of benzamides, the oxidative olefination of indole to bis(indolyl)methanes, and the decarboxylative addition of propiolic acid with indole to bis(indolyl)methanes. 10–17 Moreover, its application has also been expanded to oxidative S–P bond formation with the Ni( ii )/LA catalyst. 18 Remarkably, dioxygen was generally employed as the oxidant in these oxidation involved syntheses.…”

Transition Metal‐Catalyzed Synthesis of 1,2‐Diketones: An Overview

“…Recently, Yin and co‐workers employed a similar approach that was established earlier by Wu and co‐workers for the oxidation of internal alkynes 27 into 1,2‐diketones 28 by using Pd II /Lewis acid (AlCl 3 ) catalytic system and DMSO as the oxidant as well as solvent (Scheme 10). [30] This protocol showed broad substrate scope where a variety of internal alkynes 27 bearing aryl, heteroaryl and alkyl groups were employed to obtain the corresponding 1,2‐diketones 28 in 62–99% yields.…”

Oxidation of Diphenylacetylene in the Presence of Heterogeneous Carbon-Containing Catalysts Based on Palladium, Graphene, and Graphene Oxide

“…The simplest and most preferred method is the oxidation of 1,2-dialkylarines. However, this method has a number of disadvantages: severe conditions, long reaction time, and low yield; in addition, most oxidants are applicable only for the most common diphenylacetylene [6,7].…”