Selective Intermolecular Oxidative Cross-Coupling of Enolates

Abstract

Selective intermolecular oxidative cross-coupling of enolates, which is a bond-forming reaction between carbanion equivalents, remains as an unsolved issue despite its potential utility for the direct synthesis of unsymmetrical 1,4-diones. The main difficulty derives from the unavoidable homo-coupling. Our strategy depends on the selective one-electron oxidation of one enolate to afford an electrophilic carbonyl α-radical species, followed by trapping with another enolate. The present study demonstrates the selective oxovanadium(V)-induced cross-coupling between boron and silyl enolates.

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

“…However, selective cross‐coupling is challenging because undesired homocoupling products are often obtained. We have studied the oxidative coupling of enolates . Recently, we reported that oxovanadium(V)‐induced oxidative cross‐coupling selectively takes place by employing a combination of boron and silyl enolates in a ketone–ketone enolate coupling (Scheme b) .…”

“…We have studied the oxidative coupling of enolates . Recently, we reported that oxovanadium(V)‐induced oxidative cross‐coupling selectively takes place by employing a combination of boron and silyl enolates in a ketone–ketone enolate coupling (Scheme b) . On the other hand, carbonyl compounds including ketones, aldehydes, carboxylate, esters, and amides can also be enolate precursors.…”

“… (a) Oxidative cross‐coupling of enolates. (b) Our previous work for the V V ‐induced oxidative cross‐coupling of boron and silyl enolates derived from ketones . (c) The present work for V V ‐induced oxidative cross‐coupling of boron and silyl enolates.…”

Palladium(II)‐Catalyzed Dehydroboration via Generation of Boron Enolates

“…[3] In the original conditions, as emicatalytic amount of Pd II reagent was used with 1,4-benzoquinone. [7,8] Recently,w ed emonstrated the vanadium-induced homo- [9] and cross-coupling [10] reactions of boron enolates to give the corresponding 1,4-dicarbonyl compounds selectively.T hese findings indicatet hat the scission of boron-oxygen bonds is induced by metallic oxidants, which prompted us to investigate the functionalization of boron enolates with metallic reagents. [3b, 4] The direct Pd II -catalyzed dehydrogenation from the correspondingc arbonylc ompounds has been developed as well.…”

“…[10,11] The ether solutiono ft he obtained boron enolate 2a was successively treated with a1 .2 molar stoichiometric amount of Pd(OAc) 2 in acetonitrilea tr oom temperature. The boron enolate 2a was readily prepared from ketone 1a with commerciallya vailable 9-iodo-9-borabicyclo[3.3.1]nonane (B-I-9-BBN) in the presence of (iPr) 2 EtN (DIEA).…”