Preparation of 2‐Quinolones by Sequential Heck Reduction–Cyclization (HRC) Reactions by Using a Multitask Palladium Catalyst

Abstract

One-pot sequential Heck reduction-cyclization (HRC) reactions leading to the synthesis of substituted 2-quinolones have been developed by using a heterogeneous or mixed homogeneous/heterogeneous multitask palladium catalyst with charcoal as a support. The whole sequence occurs under very mild conditions without the need for additives (ligand or base) by taking advantage of the high reactivity of aryldiazonium salts as "super electrophiles". Recycling experiments showed that the reused heterogeneous Pd(0)/C catalyst was not able to promote another HRC sequence but was, however, still highly active for hydrogenation, hydrodehalogenation, as well as hydrogenolysis reactions.

Mizoroki–Heck Reactions with 4‐Phenoldiazonium Salts

“…The combined organic layers were dried with MgSO 4 , filtered and concentrated under reduced pressure. The residue was purified by column chromatography (silica, MTBE) to afford 9 as a colourless solid; yield: 360 mg (2.21 mmol, 73%); mp 233 8C (reported in the literature: [23] 232 8C). …”

“…Felpin et al started from a benzyl-protected diazonium salt which was converted to 9 using the Heck-reduction-cyclization-debenzylation (HRCD) sequence developed in their group. [23] We pursued a strategy that uses the acetanilide 2g as a starting material. Conversion of 2g to a phenoldiazonium salt 1g was achieved in methanol using the Table 4.…”

One‐Pot Suzuki/Heck Sequence for the Synthesis of (E)‐Stilbenes Featuring a Recyclable Silica‐Supported Palladium Catalyst via a Multi‐Component Reaction in 1,3‐Propanediol

“…In 2008, Felpin and co-workers reported the first application of Pd(0)/BaCO 3 in a Suzuki/hydrogenation sequence [9] allowing a shortened protocol toward the synthesis of bifenazate; however, in situ decomposition of the support limits to date its potential applications. Recently, the same authors provided new insights toward heterogeneous one-pot protocol via a Heck/reduction/cyclisation procedure affording either 2-quinolones [10] or oxindoles. [11,12] Previous sequences involving successive Heck/Suzuki (Djakovitch et al) [6] or Suzuki/Suzuki (Felpin et al) [13] couplings have been reported for the preparation of, respectively, 4-styrylbiphenyl and terphenyl derivatives through either I/Br (i.e., Heck) or Br/N 2 BF 4 (i.e., Suzuki) selective C À C couplings.…”

A Useful, Reliable and Safer Protocol for Hydrogenation and the Hydrogenolysis ofO‐Benzyl Groups: The In Situ Preparation of an Active Pd0/C Catalyst with Well‐Defined Properties

“…This idea was inspired by our recent work on one-pot reactions that uses a multi-task, in situ generated, Pd/C catalyst. [6] …”