Vanadium(V)‐Induced Oxidative Cross‐Coupling of Various Boron and Silyl Enolates

Abstract

Intermolecular oxidative cross-coupling of two different enolates is one of the most useful reactions to synthesize unsymmetrical 1,4-dicarbonyl compounds. In this study, the oxovanadium(V)-induced intermolecular oxidative cross-coupling of enolates afforded unsymmetrical 1,4-dicarbonyl compounds. Various boron and silyl enolates underwent the formation of ketone-ester, ester-ketone, ester-ester, amide-ketone and amide-ester coupling products . These results clearly show the versatility of the present oxidative cross-coupling protocol.

Metal-Catalyzed Oxidative Coupling of Ketones and Ketone Enolates

“…In 2017, they also showed that the same oxovanadium(V)-induced cross-coupling strategy can be extrapolated to the cross-coupling of various combinations of boron and silyl enolates in a ketone-ester, ester-ester, amide-ester, and amide-ketone enolate coupling. 22 These findings unequivocally established the versatility of this oxovanadium(V)-induced oxidative cross-coupling strategy. Scheme 6 Merged conjugate addition/oxidative coupling towards 1,4diketones…”

Enantioselective Oxidative Enolate Coupling of Oxindoles Catalyzed by Chiral Guanidinium Hypoiodite

“…Bond-forming umpolung reactions at the α-position in carbonyl groups have been well investigated, as exemplified by the well-known construction of 1,4-dicarbonyl compounds via the catalytic coupling reaction of two carbonyl enolates under oxidative conditions. − Asymmetric versions of this reaction are particularly desirable, and so far, two types of strategies have emerged for highly enantioselective catalytic asymmetric enolate coupling reaction: (i) utilizing a stoichiometric amount of a metal-based or organic oxidant, such as DDQ and CAN, in the presence of a chiral catalyst, − and (ii) electrochemical oxidation in the presence of a chiral Lewis acid . However, in the cross-coupling reaction of two different enolates, one of the enolates should be selectively prefunctionalized to avoid the generation of homotype coupling products (Figure a). ,− …”

Photochemical Synthesis of 1,4-Dicarbonyl Bifluorene Compounds via Oxidative Radical Coupling Using TEMPO as the Oxygen Atom Donor

“…The 1,4-dicarbonyl motif widely exists in various bioactive natural products and pharmaceuticals. , As a versatile building block, it is also quite useful in organic synthesis. , Thus, the syntheses of 1,4-dicarbonyl compounds have attracted attention of chemists widely. Several strategies have been developed in this field (Scheme A), including (i) Stetter reaction of aldehydes with Michael acceptors, (ii) nucleophilic substitution of enolates with α-haloketones, (iii) oxidative coupling of enolates, (iv) chain extension of 1,3-diketones, (v) acylation of homoenolate equivalents with acyl chlorides, and (vi) radical conjugate addition of acyl radicals with Michael acceptors . However, to the best of our knowledge, there have been few reports on radical coupling targeting the formation of 1,4-dicarbonyl compounds so far.…”

“…Several strategies have been developed in this field (Scheme A), including (i) Stetter reaction of aldehydes with Michael acceptors, (ii) nucleophilic substitution of enolates with α-haloketones, (iii) oxidative coupling of enolates, (iv) chain extension of 1,3-diketones, (v) acylation of homoenolate equivalents with acyl chlorides, and (vi) radical conjugate addition of acyl radicals with Michael acceptors . However, to the best of our knowledge, there have been few reports on radical coupling targeting the formation of 1,4-dicarbonyl compounds so far. In general, radical coupling reaction needs a highly functional group tolerant and mild synthetic strategy to access various organic molecules. , Therefore, it is promising to develop a new method for the synthesis of 1,4-dicarbonyl compounds via a radical coupling process, which provides more choice for synthesizing these compounds.…”