DFT Studies on the Reaction Mechanisms of 1,4-Dilithio 1,3-Dienes with Nitriles

Abstract

Mechanisms for the reactions of 1,4-dilithio-1,3-butadienes and nitriles are explored through both experiments and DFT calculations. The computational results suggest that the selectivity of these reaction systems is strongly affected by the structures of the substrates. As the first step of all reaction pathways, the addition intermediate of one C−Li bond to the nitrile is formed. When tetraalkyl-substituted 1,4dilithio 1,3-dienes and 2-cyanopyridine are used, the intermediate gives the cyclopentadienyl amine product as the kinetic product because of the coordination of the pyridyl N atom to the lithium atoms (system B). This addition intermediate also undergoes a second nitrile insertion into the C−Li bond, giving the dilithio ketimine intermediate. When tetraalkyl-substituted 1,4-dilithio 1,3-dienes and aryl nitriles are used, the dilithio ketimine intermediate undergoes a 1,6-cyclization, generating pyridine and triazine products through thermodynamically favored pathways (systems A and B). When cyclic 1,4-dilithiobutadiene and tertiary aliphatic nitriles are used, the dilithio ketimine intermediate undergoes two sequential 1,5-cyclization steps with a lower energy barrier, generating tricyclic Δ 1 -bipyrrolines (system C). Experimentally, the lithium-containing triazine intermediate 10 and Δ 1 -bipyrroline intermediate 19 have been isolated and their structures investigated through NMR and quenching experiments. The calculation results clearly show the mechanism details of these reactions and are in good agreement with the experimental observations.

Carbon‐metalated triazines and tetrazines: Synthesis and reactivity

“…Reactivity of 1,4-dilithio-1,3-diene (177) toward simple nitriles was investigated, and dilithio-1,3,5-triazine 179 was isolated by filtration among some other products, including the pyridine derivative 178 (Scheme 39). [57] Triazine 179 could be alkylated with formation of the unstable dihydro-1,3,5-triazines 180, which were spontaneously eliminated alkanes to afford the 2,4,6-triphenyl-1,3,5-triazine 44. The proposed mechanism for the formation of 179 may involve the step-wise addition of several nitrile moieties to give an imine salt 181, its further electrocyclizations into heterocycles 182 to 184, and subsequent loss of an aromatic pyridine molecule 178 (Scheme 40).…”

“…The proposed mechanism for the formation of 179 may involve the step-wise addition of several nitrile moieties to give an imine salt 181, its further electrocyclizations into heterocycles 182 to 184, and subsequent loss of an aromatic pyridine molecule 178 (Scheme 40). [57] 3.2 | Transition and other metal and metalloid derivatives (groups 3 to 14)…”

Transition Metal‐Free sp3 C–H Functionalization of Arylacetic Acids for the Synthesis of 1,3,5‐Triazines

“…In 1985, Saa et al used Fremy's salts with aromatic aldehydes for the synthesis of aryl‐substituted s‐triazines . Xi and co‐workers reported synthesis and mechanistic studies of triazines using 2,3‐dialkyl‐1,4‐dilithio‐1,3‐dienes with nitriles in the presence of hexamethylphosphoramide (HMPA), while recently Majumdar et al synthesized 1,3,5‐triazines through copper‐catalyzed cyclization of N ‐benzylbenzamidines in DMSO . 2,4,6‐Triphenyl‐1,3,5‐triazine have also been synthesized via oxidative cyclization of benzamidine hydrochloride with benzoyl isothiocyanate, benzaldehyde, benzyl alcohol, toluene etc.…”

Tuning inner-layer oxygen functional groups of reduced graphene oxide by potentiostatic oxidation for high performance electrochemical energy storage devices

“…2. Peak B at 285.2 eV corresponds to It is worthwhile to mention that the peak H at 291.8 eV is the core-excitation[26,27] and its presence indicates that there is still large sp 2 network domain exiting in the rGO electrodes after potentiostatic oxidations. Originating from the interruption of sp 2 network domain by OCFGs, the defect-induced peak A at 283.7 eV[28,29] is…”