Y- ketone

When, however, enolisation is retarded by an alkyl substituent in the methylene group, the reaction follows the same course as a- and y-ketonic esters CH3.CO.CHR.COOR -> CHa.CR (OH).CHE.COOR... 

Y = [ketone]/[phenol]0 defines the global yield, R0 = [H2]o/[phenol]0 being the ratio of fresh reactants. Theoretically, the ratio of reactants in the fresh feed should be between 2 and 3, leading to a global yield in cyclohexanone between 1 and 0. 

PriKtose, a -hydro y ketone, is then deaved into two threecarbonyl-group reactions then occur until pyruvate... 

Similar reduction [sg] of a A -y-ketone (9) gave the A -5a-olefin (10). The efficient preparation of an androst-ib-ene 12) by hydroboration of the enol acetate (ii) of the ly-ketone, and subsequent treatment with acetic anhydride [41], probably involves the same mechanism. 

In acidic media the protonated form of the ketone (19a) is considered to bond to the catalyst by accepting electrons into the formally vacant -orbital of the carbonium ion form (19b. In this case the metal-carbon bond forms most readily in the unhindered equatorial direction, so that the hydroxyl group is forced to become axial. Final hydrogenolysis of the metal-carbon bond affords the axial alcohol. Exceptions occur where the equatorial direction is exceptionally hindered, e.g. in steroidal y-ketones where selective axial bonding of the catalyst results in preponderance of the 7j - equatorial) alcohol [12,22 ]. 

This synthesis is of the same general character as that of anthracene from phenyl ortho to y ketone (p. 794). In effect it is the condensation, by the elimination of water, of phthalic anhydride and benzene with the formation of anthraquinone which we may represent as... 

As examples of ketones within the above formula, mention may be made of ethyl benzyl ketone, methyl para-isopropylbenzyl ketone, methyl meta-io y ketone, methyl butyl ketone, methyl phenylisopropyl ketone, methyl benzyl ketone and methyl para-dimethoxybenzyl ketone. 

The same type of reaction was also found for a y-diketone (eq 11) but, in this case, the product is a six-membered ring system (17) and the reaction proceeds at a much slower rate. It is interesting to note that this y-ketone also appears to react via enol formation from the terminal CH3 group rather than from the internal CH2 moiety. 

The y-ketone 135 can be made by reaction of 128 with cyclohexene oxide followed by oxidation. Baeyer-Villiger rearrangement gives mostly (24 1) the lactone 136 with the right regio-chemistry for elimination after hydrolysis to give26 only Z-137. 

Ibrahem, Cordoba and colleagues demonstrated more recently that a hydrogen-bond donor additive could accelerate the rate of the reaction, much better than the addition of water or Bronsted acid or base. In particular, thiourea 10 used as a cocatalyst (10 mol%) with OTBDMS-L-Thr (20 mol%) led to the expected (3-hydro>y ketones with configurations anti-6 or syn-7 depending on the substrate. 

Also, the Schreiner group published in 2009 a desymmetrisation approach of meso-(cyclo)alkane-l,2-diols applying the lipophilic peptide catalyst 7 (Scheme 13.8) already successfully used in kinetic resolution processes (Scheme 13.5) as previously described. The desymmetrisation step was combined in one pot with a direct TEMPO oxidation to the corresponding ot-aceto)y ketone in order to avoid racemisation of the monoacelylated intermediate. 

Figure 5.24 (a) Sulfonamide N-H - O dimer synthon in the crystal structure of bis(p-to y )ketone p-tosyihydrazone form 1 (C2/c). (b) The sulfonamide NH donor does not participate in conventional hydrogen bonding or in an N-H- n interaction in form 3 (P2j/c). The crystal structure of form 2 (C2/c) is similar to polymorph 3. The conformation about the sulfonamide moiety (r) is different in forms 1 and 3. Hirshfeld surface of polymorph 1 Is shown on the cover page... 

FIGURE 54.2 ORTEP drawings showing (a) conformer X (ketone Id) and (b) conformer Y (ketone la). 

Acyl Migration in Monocyclic and Ring-Fused Bicyclic P,y-Ketones... 

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