CO₂-Catalyzed Efficient Dehydrogenation of Amines with Detailed Mechanistic and Kinetic Studies

Abstract

Contents: 1. Materials and methods 2. General procedure for the oxidation of amines to imines 3. Setup for photocatalytic reactions 4. Optimization 5. Mechanistic experiments 6. Theoretical calculations 7. Characterization of products 8. References 9. NMR spectra Materials and methodsCommercial reagents were used without purification and reactions were run under CO2 atmosphere with exclusion of moisture from reagents using standard techniques for manipulating air-sensitive compounds. In case of dry DBN used for reactions, commercial DBN was dried over activated molecular sieves (3 Å) in a flame-dried Schlenk tube and degassed (several vacuum/argon cycles) prior to use. 1 H NMR spectra (300, 400 and 500 MHz) and 13 C NMR spectra (75.58, 100.62 and 125.71 MHz) were recorded using Bruker spectrometers AVANCE III 300, AVANCE III HD 400, AVANCE III 400, AVANCE III HD 500 and Varian spectrometers Mercury VX 300, VNMRS 300 and Inova 500 with CDCl3 and DMSO-d6 as solvent. NMR spectra were calibrated using the solvent residual signals (CDCl3: δ 1 H = 7.26, δ 13 C = 77.16; DMSO-d6: δ 1 H = 2.50, δ 13 C = 39.52; D2O: δ 1 H = 4.79). ESI mass spectra were recorded on Bruker Daltonic spectrometers maXis (ESI-QTOF-MS) and micrOTOF (ESI-TOF-MS). GC-MS mass spectra were recorded on Thermo Finnigan spectrometers TRACE (Varian GC Capillary Column; wcot fused silica coated CP-SIL 8CB for amines; 30 m x 0.25 mm x 0.25 µm) and DSQ (Varian FactorFour Capillary Column; VF-5ms 30 m x 0.25 mm x 0.25 µm). Gas chromatography was performed on an Agilent Technologies chromatograph 7890A GC System (Supelcowax 10 Fused Silica Capillary Column; 30 m x 0.32 mm x 0.25 µm). GC calibrations were carried out with authentic samples and ndodecane as an internal standard. Gas-phase GC measurements were conducted by a Shimadzu GC-2014 equipped with a TCD detector and a ShinCarbon ST 80/100 Silco column.Absorption-emission spectra were recorded on a Jasco FP-8500 Spectrofluorometer and UV/Vis spectra were recorded on a Jasco V-770 Spectrophotometer. General procedure for the dehydrogenation of amines to iminesA 10 mL two-necked flask containing a stirring bar was charged with 0.134 mmol substrate.After purging the flask three times with vacuum and two times with nitrogen the CO2 atmosphere was incorporated through a CO2-filled balloon. Afterwards dry DMSO (2.5 mL) and DBN (1.2 eq.; 0.16 mL of a 1 M solution in dry DMSO) were added. The resulting mixture was stirred for 48 h at irradiation of visible blue light (the progress can be monitored via GC-MS or TLC). Then, the resulting mixture underwent an aqueous workup (using distilled water; or brine in case of slurry phase separation) and was extracted three times with ethyl acetate.The combined organic layers were dried over anhydrous Na2SO4, filtered and concentrated in vacuo. Products were purified via silica gel chromatography with ethyl acetate and n-hexane and 1 V% triethylamine as solvents (typically 20:80 ethyl acetate:n-hexane).

A Visible‐Light Promoted Amine Oxidation Catalyzed by a Cp*Ir Complex

“…Unexpectedly, conversion was observed under these conditions, albeit to a lesser extent: ∼38 % conversion under aerobic conditions (Table ). We hypothesized that the cosolvent, DMSO present in 5 % v/v may act as the oxidizing agent in the absence of dioxygen as observed by Das and coworkers . Substituting DMSO with DMF however, led to conversion both with and without dioxygen (Table S7).…”

Post-functionalization of dibenzothiophene to functionalized biphenyls via a photoinduced thia-Baeyer-Villiger oxidation

“…Started from DBTO, in the absence of light (under air atmosphere, with PhIO as oxidant), only DBTO 2 from the oxidation of DBTO was formed in 89% yield ( Supplementary Table 1, entry 3), and lack of t-BuOOH and (or) catalyst led to reduce of DBTO to DBT (Supplementary Table 1, entries 4-6). The reaction was inhibited dramatically by radical quenchers such as (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) and butylated hydroxytoluene (BHT) suggested a radical pathway (Supplementary Table 1, entries 7-10) [51][52][53] . Furthermore, addition of 1.0 equiv.…”

“…Furthermore, addition of 1.0 equiv. of CuCl 2 to the reaction mixture resulted in the formation of BPS in 59% yield (HPLC yield) (Supplementary Table 1, entry 11), which revealed a singleelectron processes may be involved in this photochemical process [51][52][53] .…”

Recent Advances on Metal-Free, Visible-Light- Induced Catalysis for Assembling Nitrogen- and Oxygen-Based Heterocyclic Scaffolds

“…More recently, Das group also demonstrated cyclization of the diamines 189 and aldehydes 190 into heterocycles 191 , but in different reaction conditions [83] (Scheme 27). Opposite to the previous example, this protocol is based on CO 2 -catalyzed dehydrogenation/aromatization of amines under photoredox conditions.…”