N-Phosphorylated Imidazolium Salts as Precursors to 2- and 5-Phosphorylated Imidazoles and New Imidazol-2-ylidenes Featuring the PNCN Unit

Abstract

It has been experimentally proven that the reaction of 1- or 1,2-disubstituted imidazoles with diorganylphosphorus(III) halides proceeds via initial formation of N-phosporylated imidazolium salts. Treatment of these salts with strong bases results in phosphorylation of the parent imidazoles at the 2- or 5-positions, correspondingly. In a previous case, imidazol-2-ylidenes are formed as intermediates. With both N1 and N3 atoms bearing sterically demanding or/and π-donating groups, deprotonation of 1,3-disubstituted imidazolium salts with NaN(SiMe(3))(2) afforded new stable N-phosphorus-substituted Arduengo-type carbenes.

Investigation of N‐ and C‐Phosphanylation of [1,2,4]Triazolo[4,3‐a]pyridines

“…mp 126-127°C. [1,2,4]triazolo [4,3-a]pyridin-1-ium trifluoromethanesulfonate (8a) and its reaction with Et 3 N. Ph 2 PCl (5.29 g, 24.0 mmol) was added to the solution of triazole 1a (2.68 g, 22.5 mmol) and NaOTf (5.04 g, 29.3 mmol) in THF (30 mL). The mixture was stirred for 3 days at room temperature and evaporated.…”

“…Yield of compound 12a 2.41 g.(28%); mp 201-202°C. [1,2,4]triazolo [4,3-a] -5,6,7,8-tetrahydro-[1,2,4]triazolo [4,3-a] -5,6,7,8-tetrahydro- [1,2,4]triazolo [4,3-a] …”

“…A solution of t-BuLi (4.5 mL, 1.7 N in THF) was added dropwise during 15 min to a solution of [1,2,4]triazolo [4,3-a]pyridine 1a (0.89 g, 7.5 mmol) in THF (28 mL) cooled to -95 ºC. The mixture was stirred for 20 min at -95 ºC, and a solution of (t-Bu) 2 PCl (1.35 g, 7.5 mmol) in pentane (5 mL) was added during 5 min.…”

“…mp 138-139°C. 1 -5,6,7,8-tetrahydro- [1,2,4]triazolo [4,3-a]pyridine (14b). Se (0.27 g, 3.4 mmol) was added to the solution of compound 13b (0.80 g, 3.0 mmol) in benzene (6 mL).…”

“…The third approach is to treat lithium derivatives of heterocycles, containing a pyridine-type nitrogen, with phosphanylhalides (Scheme 3) [4,5,13,14]. Lithiation of heterocyclic compounds is somewhat similar to phosphanylation.…”