Metal‐free Carbon Monoxide (CO) Capture and Utilization: Formylation of Amines

Abstract

The capture and utilization of CO by 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) were performed in the absence of transition‐metal complexes. The reaction of TBD with CO afforded TBD‐CO adducts, which were converted to formylated TBD (TBD‐CHO). TBD‐CO adducts may include an interaction of CO with positively charged species based on NMR and IR analysis. In the presence of amines, CO was transferred from TBD‐CO to amines, producing formylated amines with good yields. The reaction mechanism involving TBD‐CO adducts is presented based on theoretical calculations.

Tandem Pauson‐Khand Reaction Using Carbon Dioxide as the C1‐Source

“…Carbon monoxide is an important substrate widely applied by the chemical industry in the synthesis of both bulk and fine chemicals. [1][2][3][4][5][6][7] However, CO is highly toxic and demands special handling, and consequently alternative ways of introducing the CO synthon in organic molecules are under investigation. [8] One method consists of the in situ generation of CO from other species followed by its subsequent reaction.…”

Catalytic Performance of Immobilized Sulfuric Acid on Silica Gel for N-Formylation of Amines with Triethyl Orthoformate

“…Various other formylating agents have been reported, including chloral [10], acetic formic anhydride [11], formic acid [12], ammonium formate [13], formate esters [14], polymer-supported formate [15], ethyl formate [16], triethyl orthoformate [1,2], aldehydes and methanol [17], carbon monoxide [18], and carbon dioxide [19]. However, these also tend to suffer from similar problems of long reaction times (hours to days), variable or low yields, and harsh conditions (or expensive catalyst systems).…”

“…Several catalysts have been employed for the formylation of amines, including silica-supported sulfuric acid [20], H2SO4/NaHSO4-activated charcoal [21], K-F alumina [22], Amberlite IR 120 [23], ZnO [24], nano-CeO2 [25], nano-MgO [26], natrolite zeolite [27], indium metal [28], sulfated titania [29], and sulfated tungstate [30], among others (Table 1). Various other formylating agents have been reported, including chloral [10], acetic formic anhydride [11], formic acid [12], ammonium formate [13], formate esters [14], polymer-supported formate [15], ethyl formate [16], triethyl orthoformate [1,2], aldehydes and methanol [17], carbon monoxide [18], and carbon dioxide [19]. However, these also tend to suffer from similar problems of long reaction times (hours to days), variable or low yields, and harsh conditions (or expensive catalyst systems).…”

Aerobic Oxidation of Benzylic Carbons Using a Guanidine Base

“…Owing to the resonance stabilization of its conjugate acids, TBD shows strong basicity and nucleophilicity, 21,22 resulting in its use in various organic reactions. 23−25 Previously, we reported that the TBD-mediated oxidation of benzyl mercaptans provides thiobenzaldehydes, which were employed in oxidative coupling with amines, alcohols, sulfones, and phosphorus ylides in the presence of copper catalysts (Scheme 1). 26−28 Upon comparing the acidity of benzylic C(sp 3 )–H bonds of thiols with those of amines and active methylene compounds, it was assumed that the C(sp 3 )–H bonds of amines and active methylene compounds could be cleaved by the oxygen radicals, and resulting oxygen-incorporated intermediate can undergo deprotonation by TBD to complete C=O bond formation.…”

“…Our research group has been interested in aerobic oxidation using 1,5,7-triazabicyclo[4.4.0]­dec-5-ene (TBD), a guanidine-type base. Owing to the resonance stabilization of its conjugate acids, TBD shows strong basicity and nucleophilicity, , resulting in its use in various organic reactions. − Previously, we reported that the TBD-mediated oxidation of benzyl mercaptans provides thiobenzaldehydes, which were employed in oxidative coupling with amines, alcohols, sulfones, and phosphorus ylides in the presence of copper catalysts (Scheme ). − Upon comparing the acidity of benzylic C­(sp 3 )–H bonds of thiols with those of amines and active methylene compounds, it was assumed that the C­(sp 3 )–H bonds of amines and active methylene compounds could be cleaved by the oxygen radicals, and resulting oxygen-incorporated intermediate can undergo deprotonation by TBD to complete CO bond formation. − In this study, it was found that, even in the absence of transition-metal catalysts and chemical oxidants, TBD accelerated the aerobic oxidation of amines and active methylene compounds to afford the corresponding amides and ketones selectively.…”