Carboxylic acids, aromatic, olefinic reduction

Oxidation of olefins 9-27 Oxidation of alkynes 9-65 Reductive condensation of aromatic carboxylic acids... 

On the pages which follow, general methods are illustrated for the synthesis of a wide variety of classes of organic compounds including acyl isocyanates (from amides and oxalyl chloride p. 16), epoxides (from reductive coupling of aromatic aldehydes by hexamethylphosphorous triamide p. 31), a-fluoro acids (from 1-alkenes p. 37), 0-lactams (from olefins and chlorosulfonyl isocyanate p. 51), 1 y3,5-triketones (from dianions of 1,3-diketones and esters p. 57), sulfinate esters (from disulfides, alcohols, and lead tetraacetate p. 62), carboxylic acids (from carbonylation of alcohols or olefins via carbonium-ion intermediates p. 72), sulfoxides (from sulfides and sodium periodate p. 78), carbazoles... 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1,1-difluoro olefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a l,3-dichloro-2-propanol derivative and ethyl-... 

Rhenium catalysts. H. Smith Broadbent and co-workers have reported the preparation of a number of oxides of rhenium (RcbOt. ReOj, ReOa, ReO), which are effective hydrogenation catalysts, particularly for the reduction of carboxylic acids to primary alcohols. Kor the reduction of aromatic, olefinic. carbonyl, and nitro groups they are less aclivc than nickel or plutimim calalysts hence selective hydrogenation is possible. Bcn/ylic hydroxyl groups are stable to hydrogenolysis. 

Rare earth oxides have been studied to a lesser extent than alkaline earth oxides. However, they show characteristic selectivity in the dehydration of alcohols. Secondary alcohols form 1-olefins, whereas the same reaction over an acid catalyst produces the thermodynamically more stable 2-olefin (312). An example of an industrially important rare earth oxide catalyst is Zr02. It has several applications, including the reduction of aromatic carboxylic acids with hydrogen to aldehydes (314), the dehydration of 1-cyclohexyl ethanol to vinyl cyclohexane (315), and the production of diisobutyl ketone from isobutyraldehyde (316). The extensive use of Zr02 is mainly due to its resistance to poisoning by H2O and CO2, and its inherent catalytic activity is a result of its bifunctional acid-base properties. It contains both weakly acidic and basic sites, neither of which is susceptible to poisoning. The acid-base functionality of Zr02 is displayed in the reaction of alkylamine to nitrile (278) (Fig. 33). To form nitriles from both secondary and tertiary amines, both acid and base sites are required. 

In summary, the reactivity of various functional groups toward Li 9-BBNH is classified into four broad categories [18] (1) rapid- or fast-reduction aldehyde, ketone, ester, lactone, acylchloride, acid anhydride, epoxide, disulfide, -alkyli-odide, and tosylate (2) slow-reduction tertiary amide, alkylbromide, and aromatic nitrile (3) sluggish-reduction carboxylic acid, aliphatic nitrile, primary amide, nitro and azoxy compounds, and secondary alkylbromide and tosylate (4) inert olefin, oxime, alkylchloride, sulfoxide, azo-compound, sulfide, sulfone, and sulfonic acid. 

The aromatic synthon was obtained by reduction of 3,5-dimethoxyphthalic anhydride (124) to hydroxyphthalide 125. Wittig coupling of the two fragments (125 was first converted to the sodium carboxylate 125a with dimsyl anion) and acid treatment afforded the seco acid 126 as a 1 1 mixture of olefin isomers. 

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