Lipophilic N‐Hydroxyphthalimide Catalysts for the Aerobic Oxidation of Cumene: Towards Solvent‐Free Conditions and Back

Abstract

A new class of lipophilic N-hydroxyphthalimide (NHPI) catalysts designed for the aerobic oxidation of cumene in solvent-free conditions was synthesized and tested. The specific strategy proposed for the introduction of lipophilic tails on the NHPI moiety leads to lipophilic catalysts that-while completely preserving the activity of the precursor-allow the catalytic oxidation to be conducted in neat cumene, for the first time. The corresponding cumyl hydroperoxide is obtained in good yields (28-52 %) and with high selectivity (95-97 %), under mild conditions. Importantly, the presence of a polar solvent is no longer required to guarantee complete solubilization of the catalyst. On the other hand, the oxidation conducted in neat cumene reveals the unexpected necessity of using small amounts of acetonitrile to fully promote the hydrogen atom transfer process and prevent the catalyst from detrimental hydrogen-bond (HB) driven aggregation.

Solvent‐Free Aerobic Oxidation of Ethylbenzene Promoted by NHPI/Co(II) Catalytic System: The Key Role of Ionic Liquids

“…Again, we interpret these results in term of increased solubility of Co(II) ions in the presence of IL. Interestingly, the addition of NHPI to the Co(II)/IL systems caused a further increase in the conversion of EB (Table 4, entries [13][14][15][16][17][18][19][20]. The biggest effect was observed in the CoCl 2 and Co(OAc) 2 cases.…”

“…Main research avenues comprise: i) the structural modification of the NHPI unit to increase its lipophilicity, ii) the formation of solubilizing micelles or higher aggregates; iii) the use of additives into the reaction mixture. The first approach was introduced by Ishii and co‐workers and more recently widely explored by our research group . It simply consists into the introduction of lipophilic chains on the aromatic ring of NHPI unit trying, at the same time, to avoid any increase of the bond dissociation energy (BDE) of the NO−H group which would consequently negatively affect the HAT process.…”

“…The first approach was introduced by Ishii and co-workers [12] and more recently widely explored by our research group. [13][14][15] It simply consists into the introduction of lipophilic chains on the aromatic ring of NHPI unit trying, at the same time, to avoid any increase of the bond dissociation energy (BDE) of the NOÀ H group which would consequently negatively affect the HAT process. The second approach was mainly addressed by Sasson and co-workers, and consisted in attaining partial phase transfer of NHPI into the alkylaromatic organic medium by means of formation of multilamellar vesicles made of lipophilic quaternary ammonium salts.…”

Solvent-free aerobic oxidative cleavage of alkenes catalyzed by N-hydroxyphthalimide

“…Oxidation reactions carried out in the presence of NHPI often require polar solvent due to low solubility of NHPI in hydrocarbons. As solvent elimination is an important factor in green chemistry, to overcome this problem, some lipophilic derivatives of NHPI has been synthesized and applied in solvent-free oxidations of alkylaromatics [13][14][15]. In this paper, in contrast to previous studies, the catalytic aerobic cleavage of alkenes in solvent-free conditions has been performed.…”

Iron(II)‐Catalyzed Site‐Selective Functionalization of Unactivated C(sp3)−H Bonds Guided by Alkoxyl Radicals

“…Perhaps the most striking advance of this modular protocol would be direct installation of the hydroperoxide moiety into non-oxygenated alkanes through aerobic C À H oxygenation for subsequent remote functionalization. [21] Accordingly,aone-pot 1,4-difunctionalization of non-oxygenated alkanes was established (Scheme 4). Electronically varied diaryl substituted alkanes 8a-c underwent N-hydroxyphthalimide (NHPI) catalyzed aerobic C À Ho xygenation followed by remote aliphatic fluorination, furnishing the dhydroxyl fluorides 3u, 9b,and 9c in good yields.Aryl methyl substituted (8d-f)a nd the mono-phenyl-substituted 8g were also suitable substrates when catalytic AIBN (2,2'-azobisisobutyronitrile) was applied to aerobic C À Ho xygenation, though ad ecreased yield was observed for the latter.…”