Preparation of Isocyanates from Primary Amines and Carbon Dioxide Using Mitsunobu Chemistry¹

Abstract

Primary alkylamines 1 and hindered arylamines 1 give high yields of isocyanates 5 when reacted with carbon dioxide and the Mitsunobu zwitterions 4 generated from dialkyl azodicarboxylates and Bu 3 P in dichloromethane at -78 °C. Use of Ph 3 P still gave high yields of isocyanates from reactions of primary alkylamines, but only low yields were obtained from reactions of aromatic amines. Reactions which failed to give high yields of isocyanates gave either carbamoylhydrazines 6 and/or dicarbamoylhydrazines 10 and/or triazolinones 7. The triazolinones were shown to arise from reactions of reactive aryl isocyanates with the Mitsunobu zwitterion. The carbamoylhydrazines were shown not to arise from reaction of isocyanate with reduced dialkyl azodicarboxylates, and a mechanism for their formation is proposed. Single-crystal X-ray analyses confirmed the structures of 6, 7, and 10. 3940

One‐pot synthesis of [11C]ureas via triphenylphosphinimines

“…The radioactivity was now trapped quantitatively in the vial (>99%), using THF at À608C. An explanation could be the formation of a complex between the [ 11 C]CO 2 and the amine, 16 or the increased basicity of the solution due to the amine. The initial reaction temperature was chosen similar to that used earlier for the formation of [ 11 C]2 (908C, see Scheme 2), and these conditions gave the labeled urea […”

Recent Advances in the Mitsunobu Reaction: Modified Reagents and the Quest for Chromatography‐Free Separation

“…[81] Evidence for direct acylation and a basemediated crossover step under both neutral and basic conditions has been provided. [82] Additional insights into the formation of pentacoordinate phosphorus intermediates have been furnished by 31 P NMR spectroscopy. [78,83,84] The general mechanism for the Mitsunobu reaction is outlined in Figure 8.…”

“…The products available via the Mitsunobu reaction have been expanded or the procedure has been improved to include styrene oxides with a high level of stereoretention, [32] oxetanes, [29] lactones from hindered chiral alcohols with retention of configuration, [73] aldehydes from 1,1-disubstituted-1,2-diols, [85] carbamate esters, [57,86,87] γ-lactams from amino alcohols, [88] primary amines, [89] tertiary benzylamines, [40] alkylated hydrazines, [90] nitriles, [41,61] isocyanates, [31] thiocyanates, [91] hydroxyalkyl azides, [69,92] and cisor trans-1,2-diazides from epoxides or trans-diols. [93] Hydra- zine derivatives can be obtained directly from the azodicarboxylate and an alcohol, [94] vinylhydrazinecarboxylates from ketones in the presence of dimethyl azodicarboxylate, [95] and hydrazylmethyl uracil derivatives from N 3 -benzyluracil, TMAD, and N-hydroxymethylphthalimide.…”

Kinetics of reactive absorption of carbon dioxide with solutions of 1,6-hexamethylenediamine in polar protic solvents

“…The traditional manufacturing route for organic isocyanates is by reaction of an amine with phosgene (COCl 2 ), the intermediate of this reaction is converted to the corresponding isocyanate in the presence of a nonaqueous aprotic solvent [3][4][5][6][7][8]. There is a large number of recent publications [9][10][11][12][13][14][15][16][17][18][19][20][21] in which phosgene have been replaced by a benign substitute. Use of carbon dioxide as a reagent in place of phosgene has the potential for cheaper, greener, inherently safer, and more selective route to produce carbamates, isocyanates, and polyurethanes.…”