Ketone transposition

Montuiy and Goie have developed a 1,2-ketone transposition method (Scheme 22). Baeyer-Villiger oxidation of conjugated ketone (71) afforded an enol acetate and subsequent hydrolysis revealed a carbonyl group, one carbon removed from the original position. 

This section contains alkylations of ketones and protected ketones, ketone transpositions and annulations, ring expansions and ring openings and dimerizations. Conjugate reductions and Michael alkylations of enone are listed in Section 74 (Alkyls from Alkenes). 

Jensen, B. L. Slobodzian, S. V. A concise synthesis of 1-substituted 2-tetralones by selective diol dehydration leading to ketone transposition. Tetrahedron Lett. 2000, 41, 6029-6033. 

Tchoubar, B., Sackur, O. Alkaline dehalogenation of 1-chlorocyclohexyl methyl ketone and 1-chlorocyclohexyl phenyl ketone. Transposition into a-substituted cyclohexanecarboxylic acids. Compt. rend. 1939, 208,1020-1022. 

In the development of a non-oxidative method for ketone transposition, Marshall... 

Modification of the above sequence to include reduction of the original ketone before hydrolysis is the basis for a new method of ketone transposition . For example, the keto 1,3-dithiane (21) was prepared in the... 

Woodward has now reported reliable procedures for the preparation of trimethylene and ethylene dithiotoluene-jp-sulphonates, reagents used in the formation of dithians and dithiolans from active methylene compounds, including those adjacent to a carbonyl group activated by prior hydroxy-methylene or enamine formation. Applications include carbon-carbon bond cleavage and ketone transposition (Scheme 148). 

Ketone rac-13 was transformed into the corresponding silylenolether and by Pd(II)-mediated Saegusa oxidation [14] into a, -unsaturated ketone rac-14. By alkylative enone transposition comprising methyl lithium addition and pyridinium chlorochromate (PCC) oxidation [15], rac-14 was finally converted into the racemic photo cycloaddition precursor rac-6. In conclusion, the bicyclic irradiation precursor rac-6 was synthesized in a straightforward manner from simple 1,5-cyclooctadiene (11) in nine steps and with an overall yield of 21%. 

The bismuth ylides, Ph3Bi=CHCOR, do not react with simple ketones and electron-rich olefins probably because of their relatively low electrophilic character. However, Ph3Bi=CHCOR reacts with a-keto esters [46, 67, 68], benzils [46, 67-69], orf/to-quinones [46, 67, 68], and acenaphthenequinone [70] to give epoxides, (9-arovl enolates, 3-hydroxytropones, and 3-hydroxyphenalenones, respectively, accompanied by the formation of Ph3Bi (Scheme 11). In particular, transposition and ring expansion reactions are of interest from a mechanistic point of view, since these reaction modes are unprecedented in ylide chemistry. 

Allylic zinc bromides also generally couple with ketones and acid anhydrides. In the case of trifluoroprenyl bromide, the attempts were only successful with ethyl pyruvate. However, it appears that this reaction provides the transposition product in 50% yield (equation 20). 

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