Deoxygenation, of aldehydes

The deoxygenation of aldehydes and ketones to the corresponding hydrocarbons via the hydrazones is known as the Wolff-Kishner reduction.28 Various modifications of the original protocols have been suggested. One of the most useful is the Huang-Minlon modification, which substituted hydrazine hydrate as a safer and less expensive replacement of anhydrous hydrazine. In addition, diethylene glycol together with sodium hydroxide was used to increase the reaction... 

The Clemmensen Reduction allows the deoxygenation of aldehydes or ketones, to produce the corresponding hydrocarbon. 

Since its introduction early in this century, the deoxygenation of aldehydes and ketones to methyl or methylene derivatives, respectively, via base treatment of hydrazone intermediates (equation 1) has proven to be one of the most convenient and synthetically useful processes available for this important type of transformation. The reaction is termed the Wolff-Kishner reduction in recognition of the two original independent discoverers.However, the initial recipes introduced proved tedious and unreliable with many structural, especially hindered, examples. This led to substantial efforts devoted over the years to developing more convenient and successful experimental procedures, resulting in a number of improved and more reliable modifications which are most often utilized at present. More recently, modified procedures have been provided which utilize hydride reductions of p-toluenesulfonylhydrazone (to-sylhydrazone) derivatives and subsequent decomposition to release the hydrocarbon products under much milder and less basic conditions than those normally required for Wolff-Kishner reductions (equation 2). 

The alkylation of sulfur with reactive alkylating agents, such as Mel, Me30Bp4 Et30Bp4, or MeOSOjCHj, results in 5,5-acetal deprotection without using Reductive removal of the sulfur of thioacetals with Raney-nickel (Ra-Ni) provides a frequently used procedure for deoxygenation of aldehydes or ketones. 

Ra-NL A mild procedure for deoxygenation of aldehydes or ketones is via desulfurization of their thioacetal derivatives. For example, reduction of thioacetals with Ra-Ni, derived by treatment of an Ni-Al alloy with NaOH, produces the corresponding alkane moieties. The hydrogen atoms in the deoxygenated product come from the hydrogen gas adsorbed on the Ra-Ni surface during its preparation. 

A milder approach for the deoxygenation of aldehydes and ketones involves treatment of the preformed hydrazone with t-BuO K in DMSO at room temperature. Alternatively, conversion of the carbonyl group of aldehydes and ketones into the corresponding tosylhydrazone and reduction of these with NaBH3CN ° or with (RC02)2BH produces the desired methylene compounds in good yields. 

Wolff-Kishner reduction Deoxygenation of aldehydes and ketones under basic conditions to give hydrocarbons via the corresponding hydrazones or semicarbazones. 496... 

Neumann and co-workers reported a catalytic variation of this chemistry. Labile Keggin heteropolymolybdates such as K5PV2M010O40 after activation by H2 catalyze the deoxygenation of aldehydes and ketones. For example, PhCOMe is deoxygenated to PhEt in 100% yield in the presence of K5PV2Moi0O40 supported on A1203.324... 

A very useful variant of the hydrazone reduction is the deoxygenation of aldehydes and ketones via the hydride reduction of tosylhydrazones (Caglioti reaction) The method is mild, convenient and widely applicable. While sodium borohydride was used in the earlier procedures, considerable improvements have been achieved through the uses of sodium cyanoborohydride, catecholborane, diborane, his-benzoyloxy borane and copper borohydride as reducing agents and HMPA, DMF, sulpholane, etc. as solvents. Use of the sterically crowded 2,4,6-triisopropyl tosylhydrazone derivative has greatly facilitated the reduction in some cases (equations 61-64). ... 

Inanaga has studied the use of Smiz deoxygenation of aldehydes and ketones.The reaction proceeds by a two-step mechanism, where Sml2 and CH2I2 react with the carbonyl to form an 0—SmIX species (M), which is converted to a better leaving group and reductively eliminated with Sml2." As the examples depicted in Scheme 20 indicate, no studies of chemoselectivity have been undertaken. ... 

From the following reaction with cyclohexene, it was concluded that the deoxygenation of aldehydes and ketones by Zn/Cu and TMSCI in diethyl ether takes place via a carbenoid intermediate [86a]. 

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