Reaction of Nitroxides with Sulfur Containing Compounds II [1]. Preparation of Nitroxides Bearing an Isothiocyanate Substituent in View of the Nitroxyl Group Reduction with Thiophosgene

Synthesis of Isoselenocyanates

“…Starting amines 1d-l were purchased from Aldrich, Alfa-Aesar, and Fluorochem. Nitroxyl amine TEMPO-NH 2 (1c) and its precursors were synthesized according to literature procedures: 4-(acetylamino)-2,2,6,6-tetramethylpiperidine and 4-acetylamino-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-NHCOCH 3 ), [55][56][57][58][59][60][61][62] 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (1c, TEMPO-NH 2 ). [56][57][58]61,62 Nitroxyl amines PROXYL-NH 2 (1a), 58,61,63,64 and PROXYL-CH 2 NH 2 (1b), 58,65,66 and their precursor 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-oxyl (PROX-YL-CONH 2 ) 58,67,68 were synthesized according to literature procedure with some modifications (for the protocols, see below).…”

“…Nitroxyl amine TEMPO-NH 2 (1c) and its precursors were synthesized according to literature procedures: 4-(acetylamino)-2,2,6,6-tetramethylpiperidine and 4-acetylamino-2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO-NHCOCH 3 ), [55][56][57][58][59][60][61][62] 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (1c, TEMPO-NH 2 ). [56][57][58]61,62 Nitroxyl amines PROXYL-NH 2 (1a), 58,61,63,64 and PROXYL-CH 2 NH 2 (1b), 58,65,66 and their precursor 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-oxyl (PROX-YL-CONH 2 ) 58,67,68 were synthesized according to literature procedure with some modifications (for the protocols, see below). The following protocols for TEMPO derivatives 2c, 3c, and 4c, and phenyl isoselenocyanate (4d) have been previously described: 4-(formylamino)-2,2,6,6-tetramethylpiperidin-1-oxyl (2c, TEMPO-NHCHO) in 96% yield from 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (1c, TEMPO-NH 2 ) and ethyl formate; 42 4-isocyano-2,2,6,6-tetramethylpiperidin-1oxyl (3c, TEMPO-NC) in 16% yield from 4-amino-2,2,6,6-tetramethylpiperidin-1-oxyl (1c, TEMPO-NH 2 ) using CHCl 3 and NaOH under PTC catalysis; 42 4-isocyano-2,2,6,6-tetramethylpiperidin-1-oxyl (3c, TEMPO-NC) from 4-(formylamino)-2,2,6,6-tetramethylpiperidin-1oxyl (2c, TEMPO-NHCHO) in 84% and 78% yield using either phosgene 42 or diphosgene, 25 respectively; 4-isoselenocyanato-2,2,6,6-tetramethylpiperidin-1-oxyl (4c, TEMPO-NCSe) in 38% yield 25,44 from the corresponding isocyanide 3c (TEMPO-NC), and black, finely powdered, elemental selenium in boiling CHCl 3 ; phenyl isocyanide (3d) in 66% yield from the Hofmann isonitrile reaction using aniline (1d), CHCl 3 , and NaOH under PTC catalysis; 26 phenyl isoselenocyanate (4d) in 91% yield 26 from the corresponding isocyanide 3d and black, finely powdered, elemental selenium in boiling CHCl 3 .…”

Reactions of nitroxides with sulfur-containing compounds, part IV: Synthesis of novel nitroxide (thio)ureas

“…The synthesis of 4-isothiocyanato-2,2,6,6-tetramethylpiperidine-1-oxyl 2 from 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl 1 and thiophosgene has been described earlier [19][20][21]. The reaction of the isothiocyanate 2 with corresponding secondary amines leads to the thioureas 4a-g (Table 1).…”

“…When 2,2,6,6-tetramethylpiperidine 8 was used as an amine, none of the expected (thio)ureas SCHEME 1 (i) CSCl 2 [19]; (ii) ClCOOCCl 3 , Bz 3 N, benzene; (iii) (4a-h, 5a-h) HR, benzene; (iv) (6a,b, 7a,b) HR/NaR.…”

“…4-Isothiocyanate-2,2,6,6-tetramethylpiperidin-1-oxyl 2 and 2,2,6,6-tetramethylpiperidine 8 were synthesized as described previously [19,34]. All reagents were commercially available and used as received without further purification.…”