Hydroxyamines from hydrogenation

Use is made of the facile hydrogenation of nitro groups to prepare a-hydroxy primary amines from nitromethane-ketone addition products (Eqn. 19.22). The addition of a little acetic acid to the reaction medium can sometimes improve the yield. The p-hydroxyamines are more easily prepared in this way than by the hydrogenation of the corresponding cyanohydrin. a-Chloro nitro compounds are selectively hydrogenated to the oxime over palladium under... 

For acyclic compounds the regioselectivity depends upon statistical factors and the relative acidities of the different 3-hydrogens, the elimination preferring to take place towards the most acidic hydrogen. This can also influence the regioselectivity of elimination from alicyclic compounds, e.g. the a,3-unsatu-rated carbonyl compound (14) was obtained from the 3-aminocarbonyl compound (13), and the allylic alcohol (16) was the major product obtained on oxidation and pyrolysis of the hydroxyamine (15). ... 

Pinidine (188) was recently synthesized from methyl 6-ketoheptanoate. An asymmetric electrophilic hydroxyamination of a chiral N-acylsultam was used to form the piperidine ring, and hydrogenation of the nitrone gave the required cis-2,6 substitution [466]. 

Even simple enols have substantial lifetimes, provided that bases or acids are completely excluded173. Thus, an aromatic enol 4 is prepared in situ by Norrish-type fragmentation of 2. If (-)-ephedrine is present in the reaction mixture, the enol reverts enantioselectively to (/ )-2-rnethy 1 -1 -indanone (3). With as little as 0.01 mol % catalyst, 45% ee is obtained176. The crucial enol 4 has also been generated from either the benzyl enol ester 5 by palladium on charcoal and hydrogen or from the allyl ester 6 by palladium acetate, triphenylphosphine and ammonium formate. In the presence of a chiral 1.2-hydroxyamine, e.g., ephedrine, substantial stereogenic induction in 2-methylindanone 3 was observed175. 

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