Clemmensen reduction, Table

Thioindoxyls are readily oxidized to thioindigo dyes.584 They may be reduced to benzo[6]thiophenes (Table XI) with zinc (Clemmensen reduction) or tin and acid (method a) (use of mossy zinc is preferred for the reduction of halothioindoxyls and also minimizes reduction of the thiophene ring),315 sodium borohydride (method b),222,424,432 or... 

Table 6. Acetoxycyclopropanes by Anhydrous Clemmensen Reduction of Enones in the Presence of Acetic Anhydride...

A sterically shielded cyclopropanediol has been isolated from a Clemmensen reduction.68 Other reducing conditions such as sodium dispersion in diethyl ether, lithium in tetrahydrofuran/ ammonia, or electrochemical reduction can be applied to 1,3-diketones, and the resulting cyclopropanediols can be trapped with acetic anhydride or chlorotrimethylsilane.68 -74 (see Houben-Weyl, Vol. 4/1 c, p734 Vol.6/ld, pp 656-657 Vol.6/la, part 2, p812 Vol.6/lb, p477-478). Results are summarized in Table 7. 

The main hydrogenolysis product in Table 11 and Fig. 67 is 1,3-bis(3-methyl-butyl)cyclopentane (peak numbers 6 and 7). It can be obtained separately by adsorption chromatography on silicagel with iso-octane as eluent or by vacuum distillation at 105°C and 13 mm Hg (37). Another procedure is Clemmensen reduction, followed by catalytic hydrogenation, whereby two cis-trans isomers are obtained (37). The 2,4-bis(3-methylbutyl)-2-cyclopentenone (peak number 11) can be obtained by reduction of the dihydrodeoxohumulinic acids or of compound 142 with lithium aluminium hydride and preparative gas chromatographic separation (58). 

Table 17 2 summarizes the reactions of aldehydes and ketones that you ve seen m ear her chapters All are valuable tools to the synthetic chemist Carbonyl groups provide access to hydrocarbons by Clemmensen or Wolff-Kishner reduction (Section 12 8) to alcohols by reduction (Section 15 2) or by reaction with Grignard or organolithmm reagents (Sections 14 6 and 14 7)... 

Tetrafluoro-3-oxo-4-phenylbutanoic acid is reduced at both the activated a,a -positions and the carbonyl group to give 4-phenylbutanoic acid by the Clemmensen method in quantitative yield.125 In contrast, only the highly activated C3-F bonds are selectively reduced in ethyl 2,2,4,4,4-pentafluoro-3-oxobutanoate by treatment with sodium in diethyl ether (Table 3).126 A more efficient zinc reduction of ethyl 4.4,4-trifluoro-3-oxobutanoate in refluxing acetic acid results in complete hydrodefluorination of the trifluoromethyl group to give 21.104... 

Table 7. Cyclopropanediols and Derivatives by Clemmensen or Similar Reduction of 1,3-Diones...

---