Preparation, structure, and oxidative reactivity of (dichloroiodo)pyridines: recyclable hypervalent iodine reagents

Abstract

New pyridine-based hypervalent iodine reagents, (dichloroiodo)pyridines, were prepared by chlorination of 2-, 3-, or 4-iodopyridines with NaOCl-HCl at room temperature. Structures of 2-(dichloroiodo)pyridine and 2-(dichloroiodo)-3-propoxypyridine were established by X-ray crystallography. The new (dichloroiodo)pyridines can be used as efficient reagents for oxidation of alcohols to carbonyl compounds and also as chlorinating reagents. The reduced form of the reagents such as 2-iodo-3-propoxypyridine, can be recovered from the reaction mixture in good yields by an acid-base liquid-liquid biphasic protocol.

Definition of the Halogen Bond (IUPAC Recommendations 2013): A Revisit

“…The HaB donor entity X in R–X may be the axial outer portion on the side of halogen atom X in hydrogen halides HX (X = Br, Cl, I, At) and haloalkanes (CH 3 X, CH 2 X 2 , CHX 3 (X = Cl, Br, I, At), CX 4 (X = F, Cl, Br, I, At), and C n F 2 n +1 I); the axial outer portion on the side of X in OX 2 and in dihalogen molecules X 2 and XX′ (X, X′ = F, Cl, Br, I, At); the axial outer portion on the side of X in NX 3 , as well as XCN and XCCCN (X = F, Cl, Br, I, At); the axial outer portion on the side of halogen X in halo­ethene C 2 X 4 , C 6 H 5 X, and C 6 X 6 (X = Cl, Br, I); the axial outer portion of halogen X in −NO 2 substituted arene moieties (as in 1,­3,5-tri­iodo-2,­4,6-tri­nitro­benz­ene, 2-chloro-1-iodo-4-nitro­naphth­alene, and 1,3,5-tri­chloro-2,4,6-tri­nitro­benz­ene); the axial outer portion of halogen in halo­alkynes, such as the arene derivatives (C 2 ­I 2 , halo­progin (C 9 ­H 4 ­Cl 3 IO), and 1-halo-2-phen­yl­acetyl­ene (C 8 ­H 5 ­X (X = Br, I)), 1-fluoro-4-(iodo­buta­diyn­yl)­benz­ene (C 10 ­H 4 ­FI), 2,6-bis­(iodo­ethyn­yl)­pyri­dine (C 9 ­H 3 ­I 2 ­N), 3-iodo-2-propyn­yl- N -butyl­carbam­ate, 3-(iodo­ethyn­yl)­benz­oic acid (C 9 ­H 5 ­IO 2 ), 2-(bromo­ethyn­yl)-1,3-di­chloro­benz­ene (C 8 ­H 3 ­BrCl 2 ), 1,4-di­fluoro-2,5-bis­(iodo­ethyn­yl)­benz­ene (C 10 ­H 2 ­F 2 ­I 2 ), 1,4-bis­(iodo­ethyn­yl)­benz­ene (C 10 ­H 4 ­I 2 ), 2,3-bis­(bromo­ethyn­yl)-1,4-di­meth­oxy­benz­ene, 2,2′,­4,4′,­6,6′-hexa­fluoro-3,3′,­5,5′-tetra­kis­(iodo­ethyn­yl)­bi­phen­yl (C 20 ­F 6 ­I 4 ), 1,3,5-tris­(bromo­ethyn­yl)­benzene (C 12 ­H 3 ­Br 3 ), 1,1′,1″,1‴-meth­ane­tetra­yl­tetra­kis­[4-(iodo­ethyn­yl)­benz­ene] (C 33 ­H 16 ­I 4 ), 1,3,5-tri­fluoro-2,4,6-tris­(iodo­ethyn­yl)­benz­ene (C 12 ­F 3 ­I 3 ), 1,4-bis(5-chloro-pent-4-yn­yl­oxy)­benz­ene (C 16 ­H 16 ­Cl 2 ­O 2 ), 2,6-bis­(iodo­ethyn­yl)­pyrid­ine (C 9 ­H 3 ­I 2 ), 2,3,­5,6-tetra­fluoro-1,4-bis­(iodo­ethyn­yl)­benz­ene (C 10 ­F 4 ­I 2 ), and 3-(iodo­ethyn­yl)­pyrid­ine (C 7 ­H 4 ­IN)); hypervalent halogen derivative in molecules, as in (di­chloro-tri­fluoro­meth­yl)­iodine (CCl 2 ­F 3 I), di­chloro­(phen­yl)­iodane (C 6 ­H 5 ­Cl 2 I), o -(di­chlor­iodo)­nitro­benz­ene (C 6 H 4 ­Cl 2 ­INO 2 ), p -(di­chlor­iodo)­nitro­benz­ene (C 6 ­H 4 ­Cl 2 ­INO 2 ), 2-(di­chloro­iodo)­pyrid­ine (C 5 ­H 4 Cl 2 IN), bis­(penta­fluoro­phen­yl)iodon­ium tri­fluoro­acetate (C 14 ­F 13 ­IO 2 ), tri­fluoro­meth­yl-tetra­fluoro-iodine (CF 7 I), and penta­fluoro­phen­yl-tetra­kis­(fluoro)­iodine (C 6 ­F 9 I)); the halogen in imide and amide derivatives such as N , N ′-di­bromo­ethane­di-imido­yl-di­fluoride (C 2 ­Br 2 ­F 2 ­N 2 ) and 1-chloro­pyrrol­idine-2,5-dione (C 4 ­H 4 ­ClNO ...…”

“…hypervalent halogen derivative in molecules, as in (di­chloro-tri­fluoro­meth­yl)­iodine (CCl 2 ­F 3 I), di­chloro­(phen­yl)­iodane (C 6 ­H 5 ­Cl 2 I), o -(di­chlor­iodo)­nitro­benz­ene (C 6 H 4 ­Cl 2 ­INO 2 ), p -(di­chlor­iodo)­nitro­benz­ene (C 6 ­H 4 ­Cl 2 ­INO 2 ), 2-(di­chloro­iodo)­pyrid­ine (C 5 ­H 4 Cl 2 IN), bis­(penta­fluoro­phen­yl)­iodon­ium tri­fluoro­acetate (C 14 ­F 13 ­IO 2 ), tri­fluoro­meth­yl-tetra­fluoro-iodine (CF 7 I), and penta­fluoro­phen­yl-tetra­kis­(fluoro)­iodine (C 6 ­F 9 I));…”

Recyclable Hypervalent Iodine Reagents in Modern Organic Synthesis

“…Moreover, 103 was also used for the monochlorination of 1,3-diketones. 81 The reduced form of 103 can be readily regenerated from the reaction mixture by employing an acid-base liquid-liquid biphasic protocol. 81 Rimi et al…”