Synthesis of 2, 5‐Diamino‐p—benzoquinones via Aerobic Oxidative C(sp²)‐C(sp²) Bond Cleavage and Mechanistic Studies

Abstract

A facile synthesis of 2, 5‐diamino‐p‐benzoquinones (DABQs) is reported under very mild conditions by mere crystallization. Mechanistic studies by density functional theoretical (DFT) calculations revealed an oxidative C(sp2)‐C(sp2) bond cleavage reaction mechanism via a dioxetane intermediate, from enamine oxidation of a mixture of ethyl vanillin and primary amines by triplet molecular oxygen. A second air oxidation event in the sequence of the reaction that results in C(sp2)‐C(sp2) bond formation is also described by DFT studies. The mechanistic insights enabled synthesis of both symmetric and unsymmetric DABQs from primary amines with a broad substrate scope.

Refreshing the Legacy of Rudolf Nietzki: Benzene-1,2,4,5-tetramine and Related Compounds

“…Complementary information about the structure of crystalline tetrahydrochloride salt BTA (1)•4HCl was provided by solid-state CP/MAS 13 C{ 1 H} and 15 N{ 1 H} NMR spectroscopy. The observation of only two signals in the 13 C NMR spectrum and one in the 15 N spectrum is consistent with the high molecular symmetry of the Pnnm structure and confirms the absence of significant amounts of other solid forms. 89 Structures of BTA-H 2 (2).…”

“…A standard crosspolarization pulse sequence was used with a contact time of 2 ms and a repetition time of 2.5 s. The spinning rate was in the range 10−12 kHz, and temperatures were calibrated with external PbNO 3 . Chemical shifts were calibrated on the CH 13 C signal of adamantane (set to 38.48 ppm) as an indirect reference.…”

“…This was achieved by pouring the filtrate onto ice (50 g), adding cold EtOH (4 °C, 50 mL), and inducing crystallization by adding droplets of concentrated H 2 SO 4 (ρ ≈ 1.8 g cm −3 ). The resulting precipitate was separated by filtration, washed with cold EtOH, and dried in a vacuum to give the sulfate salt of benzene-1,2,3,4-tetramine (7•H 2 SO 4 ) as a crystalline solid (0.72 g, 3.0 mmol, 37% overall yield): 1 H NMR (400 MHz, D 2 O containing added DCl to increase solubility) δ 6.78 (s, 2H); 13…”

“…Among the potential alternatives are aromatic compounds with multiple NH 2 groups and the corresponding quinonediimines, such as benzene-1,2,4,5-tetramine ( 1 ; BTA) and its oxidized form (BTA-H 2 ), which can be represented by structure 2 . Interest in compounds of this type is increasing as new green methods of amination emerge, allowing complex arylamines to be synthesized from phenolic precursors derived from renewable resources. − In addition, related aminoquinones are widespread in nature and play diverse roles, as exemplified by the antitumor antibiotic mitomycin C …”

Topology of electrostatic potential and electron density reveals a covalent to non-covalent carbon–carbon bond continuum

“…Therefore, a detailed investigation is required for exploring the bond character and the trend in eigenvalues. A selected set of such TS structures involving formation, rearrangement, cleavage 84 or activation 85 of CC bonds from various organic reactions are considered for the study and the nature of CC interaction is quantified using MESP. The V ( r ) value −0.099 to 0.428 a.u.…”