Pyridine 7V-Oxides

West and colleagues have reported the initial examples involving a N O/S O mixed donor ligand such as 2-(ethylsulphinyl)pyridine 7V-oxide for transition metal ion and lanthanide metal ion as shown in Scheme 22. Crystal field parameters based on... 

With pyridine 7V-oxides the situation is reversed in that amide ion reacts at the 4-position by the AE mechanism but at the 2-position by the EA mechanism, albeit in poor yield (Scheme 137) (67RTC655). 

Figure 11.6. SHMO orbitals and orbital energies for (a) pyrrole (b) pyridine (c) pyridinium (id) pyridine-7V-oxide (HOMO and LUMO only shown).

Bicyclic 5-6 Systems Two Heteroatoms 1 1 Table 43 Halogenation of 1 H-pyrrolo[2,3-Z ]pyridine 7V-oxide. 

The normal pattern of coupling constants for aromatic six-membered rings is found in the heterocyclic aza systems, except that the ortho coupling to a proton a to a heterocyclic nitrogen is reduced from 7-8 to 4.5-6 Hz. The /2,3 of pyrylium salts is still lower (ca. 3.5 Hz), but in pyridinium salts and pyridine 7V-oxide it is of intermediate value (ca. 6.5 Hz) (see Table 7). 

Examples treated in this book are summarized in Table 9. One frequently found type consists of ring expansions of cyclic conjugated systems with an exocyclic ylide function, such as pyridine 7V-oxides or 7V-imides incorporation of the exocyclic component of the ylide function expands the ring by one member. 

Bu ClCH2-pyridine 7V-oxide Cl l2-pyridinc /V-oxide 2004CC2602... 

Complete conversions and good enantiomeric excesses (64-100%) were achieved in the asymmetric epoxidation of chromenes and indene using UHP as oxidant and a novel dimeric homochiral Mn(III) Schiff base as catalyst. The reactions were carried out in the presence of carboxylate salts and nitrogen and oxygen coordinating co-catalysts. However, the epoxidation of styrene unfortunately proceeded with incomplete conversion and only 23% ee. Modification of the catalyst and use of pyridine 7V-oxide as cocatalyst allowed improvement of the ee to 61% (Scheme 18). ... 

Pyridine 7V-oxide cyclizes 3-aminopyrazoles to give a low yield of a tricyclic product. The reactive S,5-dimethyIsulphimides (see Chapter S3, Section IL9) are cyclized in a mild reaction with a nitrile oxide (reviews [B-43, 2115] to produce the triazole 1-oxide in good yield. The chemistry of [l,2,4]triazolo[l,5-... 

Af-Oxide chemistry in these bicyclic systems largely parallels the processes described for pyridine 7V-oxide, with the additional possibility of benzene ring electrophilic susbstitution, for example mixed acid nitration of quinoline A -oxide takes place at C-5 and C-8 via the O-protonated species, but at C-4 at lower acid strength nitration of isoquinoline A/ -oxide takes place at C-5. ... 

Complexes with pyridine 7V-oxide of zinc thiocyanate and selenocyanate of the stoichiometry ZnLsX2 (X = SCN, SeCN) have been reported. IR evidence shows that they are best formulated as [ZnI ] [ZnX4f. ... 

In 1964, the syntheses of the cationic tris[l-oxopyridin-2-olato(l-)]-silicon(IV) complexes 39 1 were claimed, " based on elemental analyses and ESCA data for 39. " Very recently, we succeeded in synthesizing and characterizing the related complexes 42-44 (synthesis of 42 Scheme 24.5). Compound 42 C5H5NO2 (C5H5NO2 = l-hydroxy-2-pyridone or 2-hydroxy-pyridine 7V-oxide) was structurally characterized by single-crystal X-ray diffraction the Si coordination polyhedron was found to be a distorted octahedron. 

There are many examples of Passerini-tj e reactions mediated by Lewis acids with TiCU having the most widespread use. Passerini-type reactions using TiCU are compatible with a variety of functional groups as can be seen in the nearly quantitative reaction of a-isocyano phosphonate ester 25 with benzaldehyde. An examination of TiCU-mediated diastereoselective Passerini reaction failed to show any clear stereoselection with chiral isocyanide 26 among many other cases. Weaker Lewis acids such as SiCL can also mediate Passerini-twe reactions, but effectively do so only in the presence of a Lewis base. Demnark demonstrated that a-hydroxyamides, such as 27, could be formed in good yields, by using Lewis bases such as pyridine-7V-oxide to activate the SiCU-... 

Pyridine 7V-oxides and the iNT-oxides of pyrimidine and pyrazine absorb strongly at 1320-1200 cm due to the NO stretching frequency. A second band is found at 880-845 cm ... 

P3Tidlne (0.5 equiv) TS2O (1.2 equiv) Pyridine 7V-oxide (1.2 equiv)... 

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