Dehydrogenation with chloranil

Chlormadinone (38) is prepared from hydroxyprogesterone (39) by epoxidation and treatment of the epoxide with hydrochloric acid to provide the chloroalkene (40). Oxidation, ie, dehydrogenation, with chloranil, provides chlormadinone (38), which may be acetylated to provide chlormadinone acetate (63,64). 

Ir a similar reaction, Ruccia et al.109 obtained adducts 104 when substituted indoles were treated with nitrilimines. Two of these adducts were readily dehydrogenated with chloranil in xylene to give the pyrazolo[3,4-ft]indoles (105). 

Aromatizations play a particularly prominent role in the synthesis of carbazoles since both the Fischer cyclization (Borsche s method) of cyclohexanones (Section 3.06.3.4.2) and the cycloaddition of 2-vinylindole (Section 3.06.6.1) yield tetrahydrocarbazoles. Both catalytic dehydrogenation over palladium/carbon catalyst and dehydrogenation with chloranil have been employed to effect aromatization (80JA4772,79JOC4402). 

We have too little information to understand the reactivity of azomethine ylides toward nonactivated acetylenes since acetylenes bearing no electron-withdrawing substituent(s) have rarely been utilized in cycloaddition trapping of azomethine ylides. To the best of our knowledge, the only example is the reaction of azomethine ylide 7, stabilized by two ester moieties, with acetylene itself in acetone at 125°C, producing pyrrole 210 after dehydrogenation with chloranil (66TL397). 

Many years after the classical investigations of the production of minute amounts of aromatic hydrocarbons by selenium dehydrogenation of steroids, Dannenberg found (1956-63) that steroids can be dehydrogenated with chloranil in refluxing xylene or anisole to give optically active aromatized hydrocarbons in yields up to 50%. Cholesterol affords 3-methyl-3 -isooctyl-A -l,2-cyclopentadienophenanthrene (13) and its methyl derivative (14). 

C23 hydrogens. These two products are also obtained by dehydrogenation with chloranil. 

A number of quinoxalinones have been prepared by reaction of o-phenylenediamine with N-arylmaleimides (13). The initially formed di-hydroquinoxalinones are subsequently dehydrogenated with chloranil (Scheme 3). When o-phenylenediamines are condensed with alloxan... 

Condensation of p-O-methoxyphenylhydrazine (74S) with 2,5-dimethylcyclohexanone (746) gave mainly the tetrahydrocarbazole 747, which was dehydrogenated with chloranil in refluxing THF. The resulting carbazole 746 was formylated under Vilsmeier-Haack conditions to afford 744. Formation of the pyridine ring can then be achieved by condensation with the diethylacetal of aminoacetaldehyde followed by reduction of the imine, N-tosylation, and cyclization to give 743 as described previously (Scheme 57). When the 4-methyl group is not present in the carbazole 748,... 

Diketones (XU-100) and benzaldazine give l-benzylideneimino-2,3-dihydro-4-pyridones (XII-101), which can be converted to the corresponding 2,3-di-hydro-4-pyridones (XI-102)by hydrogenolysis. Dehydrogenation with chloranil gives the 4-pyridone. 

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