Ketones conjugation effects

When isomerization of 100-g. batches of non-conjugated ketone was effected in ethanol under catalysis by either hydrochloric acid or sodium hydroxide (followed by neutralization of the yellow enolate solution with acetic acid), a permanent yellow coloration developed, the first-crop material was yellowish and melted at 78-80°, and the second-crop material was very impure. 

The fundamental concept of inductive and field effects introduced for carboxylic acids can be applied to weaker acids such as the a-hydrogen of ketones. Reaction of 12 with a strong base, in Zoretic s synthesis of megaphone,illustrates this premise. Both Ha and Hb in 12 are acidic, but Ha is preferentially removed by virtue of its proximity to the carbonyl (secs. 9.1, 9.2). Although Hb is acidic by the conjugating effect of the It bond (it is a vinylogous acid), the effect is diminished due to the distance from the carbonyl. Formation of the enolate is followed by alkylation (secs. 2.7.A, 9.3.A) to provide 13 in good yield. 

Conversion of ketones into olefins (3, 98). This reaction can be effected by conversion to the thermodynamically controlled enol phosphate with diethyl phosphorochloridate in TMEDA followed by reduction. Originally lithium in NH3 or C2H5NH2 was used for this step. Titanium metal is more effective, except for ketones conjugated to aromatic rings. ... 

Only a few papers have been published regarding the polymerization of ot,p-unsaturated ketones begun with cationic initiators. This reflects the fact that stabilization of the active center by the conjugative effect of the carbonyl group is not as simple as in anionic-initiated polymerization. Coleman [369] and Schildknecht [370] describe the homopolymerization of some perfluoralkyl propenyl ketones with boron trifluoride at -80° C in bulk and in solution. However, the resulting products have not been characterized adequately. 

Conjugate addition of O-alkylhydroxylamines to a,P-unsaturated ketones was effectively catalyzed by an isolable complex of scandium with a chiral phosphate ligand (Sc[(R)-BNP]3) [124]. The corresponding P-amino ketones were generated in almost quantitative yields with high enantioselectivities (Scheme 12.48). These products could be quantitatively converted into the 2-acyl aziridines upon treatment with a base catalyst without losing their enantiopurities. 

Aldol condensation offers an effective route to a p unsaturated aldehydes and ketones These compounds have some interesting properties that result from conjugation of the carbon-carbon double bond with the carbonyl group As shown m Figure 18 6 the rr systems of the carbon-carbon and carbon-oxygen double bonds overlap to form an extended rr system that permits increased electron delocalization... 

For the reduction of conjugated enones to saturated alcohols, Procedure 5 (section V) may be modified by adding methanol in place of ammonium chloride a sufficient excess of lithium is present to effect reduction of the intermediate saturated ketone to the alcohol. Procedure 2 (section V) for effecting Birch reductions is also useful for reduction of conjugated enones to saturated alcohols. Thus, 17-ethyl-19-nortestosterone affords crude 17a-ethyl-5a-estrane-3) ,17) -diol of mp 174-181°, reported mp 181-183°, in quantitative yield. 

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