Salicylato Titanocene Complexes as Cooperative Organometallic Lewis Acid and Brønsted Acid Catalysts for Three‐Component Mannich Reactions

Abstract

A binary acid system has been developed that features an air-stable organometallic precursor, titanocene dichloride, and simple organic cooperative Brønsted acids, which allowed for mild and highly efficient Mannich reactions of both aryl and alkyl ketones with excellent yields and satisfactory diastereoselectivity. Mechanistic studies, including (1) H NMR titration, X-ray structure analyses as well as isolation of catalytically active species, elucidated the dramatic synergistic effects of this new binary acid system.

Hf(OTf)4 as a Highly Potent Catalyst for the Synthesis of Mannich Bases under Solvent-Free Conditions

“…Flash column chromatography (hexane/ethyl acetate 10:1) afforded the desired Mannich base in pure form. The characterization data of Mannich bases 1-10, 12-14, 17-19, 24, 26, and 30-32 were in good agreement with those reported in literatures [17,19,20,22,25,36,[47][48][49][50].…”

Computational and Experimental Study on Molecular Structure of Benzo[g]pyrimido[4,5-b]quinoline Derivatives: Preference of Linear over the Angular Isomer

“…results suggest that the electronic nature of the substituent on aromatic aldehydes and the pyrimidin-4-ones have no significant effect on rate, yields and the course to lead to aromatization of pyridinic ring. This protocol is a like a Mannich-type reaction, which compared with conventional methods, does not require long reaction times, and the use of flammable solvents, or expensive and toxic catalysts (ionic liquids, superacid, Brønsted acids), to obtain regioselectivelly the reaction products [40,41,43,44].…”

“…In these reactions, also reported by other researches, the dihydroderivatives are obtained as final products (Scheme 1) [37,38]. Continuing with our studies for the synthesis of aza-heterocycles, we have decided to investigate the MCR of 6-aminopyrimidin-4-ones 1, naphthalene-1,2,4(3H)-trione 2 and aromatic aldehydes 3 under MW irradiation and solvent-free/catalyst free conditions in order to obtain benzopyrimidoquinolines, and so providing results for a comparative analysis with previous reported experiments [39] and the better knowledge of the reaction type involved in the formation of carbon-carbon bonds [40,41].…”

N-Donor ligand activation of titanocene for the Biginelli reaction via the imine mechanism

“…Our group has long been involved in modulating the Lewis acidity of group IVB metallocenes like Cp 2 TiCl 2 . [20][21][22] Until now, the successful activation strategies for Cp 2 TiCl 2 primarily involve Odonor or P-donor ligands to form more active species, such as 25 Through the in situ establishment of those active titanocene-based Lewis acids, many organic transformations like the Mannich [26][27][28] and Friedel-Cras reactions 29 have been realized with satisfying yields (Scheme 1). The reason that Ti(IV)-N bond-containing complexes are rare can be partially attributed to the weakness of Ti(IV)-N bonding compared with Ti(IV)-O bonding, 30 although weaker Ti(IV)-N bonding may feature stronger catalytic activity.…”