Hydroxy-, derivatives ketones, properties

The reduction of an unsymmetrical ketone creates a new stereo center. Because of the importance of hydroxy groups both in synthesis and in relation to the properties of molecules, including biological activity, there has been a great deal of effort directed toward enantioselective reduction of ketones. One approach is to use chiral borohydride reagents.92 Boranes derived from chiral alkenes can be converted to borohydrides, and there has been much study of the enantioselectivity of these reagents. Several of the reagents are commercially available. 

The synthesis and characterization of V02+ complexes of hydrazones (94) and (95) derived from benzoylhydrazine and o-hydroxy aromatic aldehydes and ketones were also reported772 and molecular weight determinations, IR, electronic spectra and magnetic properties were explained assuming a dimeric structure (96) with each unit having a five-coordinate square pyramidal geometry. 

With the enantioselective intramolecular benzoin reaction established as a synthetic tool, and in combination with our efforts in the synthesis of bioactive natural products bearing a quaternary a-hydroxy ketone unit (Davis and Weismiller 1990 Heller and Tamm 1981), such as the 4-chromanone derivative (S)-eucomol (Bohler and Tamm 1967 Crouch et al. 1999), a catalytic asymmetric synthesis of various 3-hydroxy-4-chromanones brought about by the chiral triazolium salts 127, 123b and 102 as pre-catalysts was investigated (Enders et al. 2006d). The sterically different pre-catalysts were chosen in order to adjust the catalyst system to the steric and electronic properties of the substrates 128. A screening of the reaction conditions indicated 10 mol% of the... 

Hydroxycodeinone was first represented as an a-hydroxy-ketone, but such a formulation was rejected by Gulland and Robinson [9] on account of the stability of the base towards alkaline silver and cupric solutions, and, moreover, the base does not behave as an allylamine in its reaction with cyanogen bromide [4, 13-16]. A /3-hydroxy-ketone structure was never seriously considered and is in any case at variance with the observed difficulty of dehydrating 14-hydroxycodeinone and its derivatives, but a y-hydroxy-ketone formulation is compatible with all the experimental facts. 14 Hydroxycodeinone does not show the properties of a methylene-ketone, but its dihydro-compound does, facts best explained by postulating the presence of the system —GO—0—C—C—OH in the former [9]. 

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