Allylic and Allenylic Dearomatization of Indoles Promoted by Graphene Oxide by Covalent Grafting Activation Mode

Abstract

The site‐selective allylative and allenylative dearomatization of indoles with alcohols was performed under carbocatalytic regime in the presence of graphene oxide (GO, 10 wt % loading) as the promoter. Metal‐free conditions, absence of stoichiometric additive, environmentally friendly conditions (H2O/CH3CN, 55 °C, 6 h), broad substrate scope (33 examples, yield up to 92 %) and excellent site‐ and stereoselectivity characterize the present methodology. Moreover, a covalent activation model exerted by GO functionalities was corroborated by spectroscopic, experimental and computational evidences. Recovering and regeneration of the GO catalyst through simple acidic treatment was also documented.

Study and application of graphene oxide in the synthesis of 2,3-disubstituted quinolinesviaa Povarov multicomponent reaction and subsequent oxidation

“…In order to clarify the nature of the interaction between the organic molecules and GO, we treated the recovered GO under acidic conditions, 62 and we repeated the XPS analysis, finding no significant variation in GO's chemical structure: the O/C ratio slightly decreased, but N and Cl amounts were identical to in the untreated sample. Acid treatment apparently was not able to regenerate the GO as previously reported, 61 probably due to the presence of grafted reagents on the active sites. Moreover, we carried out the Povarov reaction using the GO recovered after acidic treatment, but it gave 1a in only a 17% yield.…”

“…To improve the conversion of the less reactive substrates, we slightly changed the reaction conditions, applying longer time and/or higher reaction temperature, affording the products in acceptable yields and with endo as the major isomer. For compound 1r, where surprisingly the inversion of diastereoselectivity was observed, we tried to improve the yield by using a mixture of CH 3 CN/H 2 O as 4 : 1, 61 showing an increase in the yield from 28% to 40%.…”

The syntheses, structures and spectroelectrochemical properties of 6-oxo-verdazyl derivatives bearing surface anchoring groups

“…[4-Methylphenyl]hydrazine 87 . A Schlenk flask was charged with 4-methylaniline (4.01 g, 37.3 mmol) in 32% (w) HCl (60 mL).…”

Graphene Oxide as a Mediator in Organic Synthesis: a Mechanistic Focus

“…Very recently,o ur group has extended this methodology to the dearomative allylation/allenylation of 2,3-disubstituted indoles 10 with allylic and propargylic alcohols 7. [30] The reaction conditions appeared extremely interesting from as ustainable point of view since required only 10 wt %o f GO,aqueous media and low temperatures (55 8 8C, Scheme 7). It is worth mentioning that the use of alcohols in dearomative protocols commonly requires expensive noble metal-catalysis, rigorous anhydrous conditions and stoichiometric acid or base additives.…”

“…Very recently, our group has extended this methodology to the dearomative allylation/allenylation of 2,3‐disubstituted indoles 10 with allylic and propargylic alcohols 7 [30] . The reaction conditions appeared extremely interesting from a sustainable point of view since required only 10 wt % of GO, aqueous media and low temperatures (55 °C, Scheme 7).…”