Synthesis and characterization of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide: X-ray structure of 4-methoxy-3-(sulfanylmethyl)- and 4-chloro-3-(selenenylbenzyl)-N,N-diisopropylpyridine-2-carboxamide

Synthesis of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide (1a and 1b respectively) has been reported. 1a and 1b were lithiated with 2 equiv. of n-BuLi or LDA at −78 °C. Addition of elemental sulfur or selenium to the carbanion led to the formation of corresponding thiolate or selenolate anions respectively. The selenolate anions were aerial oxidized to afford the corresponding diselenides. The thiolate/selenolate anions were quenched with a variety of electrophiles to give unsymmetrical thio/selenoalkanes in moderate to good yields. Reductive cleavage of Se–Se bond has also been studied. The synthesized compounds were characterized by elemental analysis, NMR (1H, 13C and 77Se), FT-IR and mass spectral techniques. Crystal structures of two compounds, 6b and 7a, were determined by single crystal X-ray crystallography. Their crystal structure exhibits 1,4-type S⋯OCH3 and Se⋯Cl intramolecular secondary interactions respectively. The relative thermal stability of 3a, 3b and 4a has also been established by thermogravimetric analysis.

A one pot synthesis of chalcogen derivatives of 4-chloro-/4-methoxy-N,N-diisopropylpyridine-2-carboxamide has been reported. The crystal structure of unsymmetrical monochalcogenides exhibits 1,4-type E⋯X (X = Cl, O) intramolecular non-bonded interactions.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of organochalcogens containing N,N-diisopropylpyridine-2-carboxamide ring.
► Presence 1,4-type E⋯X intramolecular non-bonded interactions in these compounds.
► The diselenides are thermally more stable than the monoselenides.