Wolff-Kishner reduction rearrangement

Williamson synthesis Wohl-Ziegler reaction Wolff rearrangement Wolff Kishner reduction Wurtz reaction Wurtz-Fittig reaction... 

Beckmann rearrangement, 4, 292 pyrolysis, 4, 202 synthesis, 4, 223 Wittig reaction, 4, 294 Wolff-Kishner reduction, 4, 291 Indole, 1-acyl-2,3-disubstituted photoisomerization, 4, 204 photo-Fries rearrangement, 4, 204 photoisomerization, 4, 42 synthesis, 4, 82 Indole, 2-acyl acidity, 4, 297 synthesis, 4, 337, 360 Indole, 3-acyl-acidity, 4, 297 cleavage, 4, 289 reduction, 4, 289 synthesis, 4, 360 Indole, 7-acyl-synthesis, 4, 246... 

Methyl- or 2-ethyl-benzo[Z> ]thiophenes are conveniently prepared by treatment of 2-benzo[6]thienyllithium with the appropriate alkyl sulfate <70AHC(11)177). Clemmensen or Wolff-Kishner reductions of the 2-acylbenzo[Z>]thiophenes are useful, but since acylation produces a mixture of the 2- and 3-acyl isomers (Section 3.14.2.4), these must be separated. Cyclization of phenyl phenacyl sulfide with hydrofluoric acid leads exclusively to 2-phenyl-benzo[6]thiophene, and 3-phenylbenzo[6]thiophene can be rearranged to the 2-isomer in hydrofluoric acid (Section 3.15.2.3.2). Aromatization of 2-cycIohexenylbenzo[6]thiophene, obtained by condensation of the 2-lithio reagent with cyclohexanone, gives 2-phenyl-benzo[6]thiophene, and the reaction is adaptable to the 2-(l-naphthyl) derivative also. 

A plethora of products is obtained when either elemol (273), in the presence of p-nitrobenzoic acid (or benzoic acid), or elemyl-p-nitrobenzoate is pyrolysed at about 200 °C. These include the elemenes (274)—(276) together with the selinenes (277)—(281). The sequence of formation and the factors affecting the thermolyses are discussed in depth, together with the data for the thermolysis of dihydro-geijerene (282). This latter compound has been synthesized from germacrone (227) by a Cope rearrangement to j3-elemenone (283) followed by a retro-aldoliza-tion to (284) and subsequent Wolff-Kishner reduction. 

In their synthesis of fukinone, Marshall and Cohen converted the known ene-ol (340) into (341) by acetylation, allylic oxidation, and conjugate methylation with dimethylcopperlithium. A Wolff-Kishner reduction of (341) followed by oxidation of the resultant alcohol and enol-acetylation yielded (342). The epoxide of (342) was thermolysed to give (343) which, on reaction with iso-propenyl-lithium and selective oxidation, gave the ketol (344) which was converted in two steps into fukinone (335). A number of sesquiterpenoids, e.g. fukinanolide (345), with the rearranged eremophilane skeleton viz. fukinane (346 R = Me) are known. Nay a and Kobayashi have now prepared this parent hydrocarbon by Raney nickel reduction of the thioacetal of fukinan-8-al (346 R = CHO). 

The most important side-chain conversion involves reduction of ketones either by amalgamated zinc and HCl (Clemmensen reduction) or by hydrazine and strong base Wolff-Kishner reduction). This method is important because the necessary ketones are readily available through a modification of the Friedel-Crafts reaction that involves acid chlorides (see Sec. 19.6). Unlike alkylation by the Friedel-Crafts reaction, this method does not involve rearrangement. 

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