Wolff mechanism

Photochemical Wolff rearrangement of 2-diazo-3-ketones, though not widely used as a source of A-norsteroids, is discussed in section V in connection with the mechanism of the important photochemical synthesis of D-norsteroids. Photochemical rearrangement of epoxy ketones is a source of A-nosteroids these rearrangements are discussed in chapter 13. Other photochemical routes to A-norsteroids are known." " ... 

Figure 19.11 MECHANISM Mechanism of the Wolff-Kishner reduction of an aldehyde or ketone to yield an alkane.

The photolysis of o-quinone diazides was carefully investigated by Stis in 1944, many years before the development of photoresists. Scheme 10-102 shows the photolysis sequence for the diazoquinone 10.75 formed in the diazotization of 2-amino-1-naphthol. The product of the photolytic step is a ketocarbene (10.76), which undergoes a Wolff rearrangement to a ketene (10.77). In the presence of water in-dene-3-carboxylic acid (10.78) is formed this compound is highly soluble in water and can be removed in the development step. The mechanism given in Scheme 10-102 was not postulated as such by Stis, because in 1944 ketocarbenes were unknown (for a mechanistic discussion of such Wolff rearrangements see review by Zollinger, 1995, Sec. 8.6, and Andraos et al., 1994). 

When the Wolff rearrangement is carried out photochemically, the mechanism is basically the same, but another pathway can intervene. Some of the ketocarbene orieinallv formed can undergo a carbene-carbene rearrangement, through an oxi-... 

The first step in the mechanism of the Wolff-Kishner reaction consists of formation of the hydrazone (16-19). 

Not much is known about the mechanism of the Clemmensen reduction. Several mechanisms have been proposed, " including one going through a zinc-carbene intermediate. " One thing reasonably certain is that the corresponding alcohol is not an intermediate, since alcohols prepared in other ways fail to give the reaction. Note that the alcohol is not an intermediate in the Wolff-Kishner reduction either. 

Figure 3.2 Proposed mechanisms of protein modification through carbonyi interactions involving monosaccharides [from Brownlee et af. (1988) and Wolff and Dean (1987)].

Wolff-Kishner reduction of ketones bearing other functional groups sometimes gives products other than the expected methylene reduction product. Several examples are given below. Indicate a mechanism for each reaction. 

The mechanism through which a-methylmercury substituents eliminate Wolff rearrangements of acyl- and carboalkoxymethylenes is not clearly evident. 

Lazrak, T., A. Milon, G. Wolff, A.M. Albrecht, M. Miehe, G. Ourisson, and Y. Nakatani. 1987. Comparison of the effects of inserted C40- and C50-terminally dihydroxylated carotenoids on the mechanical properties of various phospholipid vesicles. Biochim. Biophys. Acta 903 132-141. 

The one-step mechanism, depicted in path a, consists simply of a 1,2-shift of an ortho carbon. While this process is an all-carbon version of the Wolff rearrangement, the bond order of the migrating bond is substantially greater than 1.0. Hence this would represent an unprecedented reaction of carbenes. 

Hydrazones are important intermediates in a Wolff-Kishner reduction, a procedure for reducing a carbonyl group. An example of a Wolff-Kishner reduction appears in Figure 10-27, and the mechanism is in Figure 10-28. 

For the heterogeneous reactions of HCl on PSCs and aerosols to be important, there must be mechanisms to continuously provide HCl to the surface. This could occur, for example, if HCl is sufficiently soluble in ice and if it diffuses at a sufficient rate from the bulk to the surface. However, the solubility and diffusion rates have been shown to be sufficiently small that these processes are not expected to be important under stratospheric conditions (see Wolff and Mulvaney, 1991 Domine et al., 1994 and Thibert and Domine, 1997). 

The thyroid gland also regulates its uptake of iodide and thyroid hormone synthesis by intrathyroidal mechanisms that are independent of TSH. These mechanisms are primarily related to the level of iodine in the blood. Large doses of iodine inhibit iodide organification (Wolff-Chaikoff block, see Figure 38-1). In certain disease states (eg, Hashimoto s thyroiditis), this can inhibit thyroid hormone synthesis and result in hypothyroidism. Hyperthyroidism can result from the loss of the Wolff-Chaikoff block in susceptible individuals (eg, multinodular goiter). 

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