Alkyl sulfates with oximes

Thermal synthesis of 2-substituted phenanthroxazoles and related compounds by cyclization of O-methyl o-quinone oximes with compounds ArCH2Y (Ar = aryl, hetaryl Y = H, OH, Cl, Br, OAc, SH, COR, NH2) or with amines (PhCHiNMej, PhNHMe, PhNMe2) has been described. Cyclization of a-oxooximes in the system alkyl halide or sulfate/DMF/K2C03 also leads to oxazole derivatives . 

The use of mediators to improve reactivity or selectivity in nitrone cycloaddition chemistry begins with the nitrone generation step. As is well known, the N-alkyla-tion of oximes provides one of the most direct and convenient synthetic routes to N-alkylated nitrones from readily available aldehydes and ketones. Electrophilic mediators have been employed to activate alkenes for N-alkylation, both in intramolecular and intermolecular reactions. They include activation of the internal alkene function by the action of (a) strong nonmetallic electrophiles such as phenyl-selenenyl sulfate (159), and (b) metallic catalysts such as Ag(I) (160) and Pd(II) ions... 

Acetyl-4-hydroxy-6-methyl-2-pyridone oxime, 641 5 -Acetyl-4-hydroxy-6-methyl-2-pyridone, 634 acetylation, 658, 816 N-alkylation with dimethyl sulfate, 765... 

An interesting and unusual synthesis of racemic leucine (Leu, L) was carried out as shown in Scheme 12.34 and reported early in the twentieth century. As shown, 2-methyl-l-propanol was converted to the corresponding iodide with hydrogen iodide (HI) and the primary alkyl iodide reacted with sodium salt derived from methyl acetoacetate to yield 5-methyl-3-carboxymethyl-2-hexanone. This, treated with nitrosyl sulfate (0=N-0S03H), yields the decarbonylated methyl 5-methyl-pentanoate-2-oxime. Reduction of the latter produced racemic leucine (Leu, L). 

Other alkylation processes include the O-methylation of oximes, A-oxides, hydroxylamines, and hydroxamic acids. The preparation of oxime ethers using dimethyl sulfate has proven an effective methodology for the construction of sidechains designed for new cephalosporin antibiotics. Treatment of a-oxime esters with dimethyl sulfate afforded the a-methoximino esters, which were subsequently hydrolyzed to the acid and used as sidechains via acylation chemistry (eq 8). ... 

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