Wolff products

The Wolff rearrangement of anti- and syn- dehydronorbomyl compounds 69 in methanol resulted in the formation of unexpected rearranged products 70-72. The photolysis of 69-anti gave five isomers viz. 70 -anti-exo, 10-anti-endo and the unexpected products l -anti-endo, l -anti-exo and 12-anti. The diazo ketone 69-syn led to two abnormal Wolff products 71 and 72 in addition to the expected Wolff rearrangement product. 

The disadvantages associated with the Clemmensen reduction of carbonyl compounds (see 3 above), viz., (a) the production of small amounts of carbinols and unsaturated compounds as by-products, (h) the poor results obtained with many compounds of high molecular weight, (c) the non-appUcability to furan and pyrrole compounds (owing to their sensitivity to acids), and (d) the sensitivity to steric hindrance, are absent in the modified Wolff-Kishner reduction. 

Aryl-4,5-dihydropyridazine-3(2//)-one undergoes ring opening when submitted to Wolff-Kishner reduction, while with lithium aluminum hydride the corresponding 2,3,4,5-tetrahydro product is obtained. 

Both the Wolff-Kishner and Clemmensen reductions of a, -unsaturated ketones give olefins. There has been considerable confusion concerning the exact product composition in the case of A -3-ketones. Wolff-Kishner reduction gives A" -, 5a-A - and 5 -A -olefins, and, depending on the substrate reaction conditions and work-up, any one or more of these may be isolated. (See ref. 287 for a recent review of the Wolff-Kishner reduction.)... 

The stereochemistry of the product resulting from the reaction of a 17-keto steroid with ethylidenetriphenylphosphorane is different from that of the 17-ethylidene steroids obtained by dehydration of 17a-ethyl-17/ -hydroxy compounds, Wolff-Kishner reduction of A -20-keto steroids or by sodium-alcohol or sodium-ammonia " reductions of 17-ethynyl carbinols. These latter products have generally been assumed to possess the trans configuration (C-21 methyl away from the bulk of the ring system) because of anticipated greater stability. The cis configuration for... 

B-norketone (119) by enlarging ring A with diazomethane to give A-homo-B-norketone (120). Wolff-Kishner reduction of (120) gave hydrocarbon (118) identical to the product from ketone (116a). 

The conditions described for the preparation of the semi-carbazone are critical and should be strictly observed. Otherwise, the yield of the product in the subsequent Wolff-Kishner reduction is decreased. 

Based on observations by Bamberger, Bucherer, and Wolff at the turn of the century, Matrka et al. (1967) described experiments which show that alkaline solutions (pH 8.5-9.2) of substituted benzenediazonium chlorides form nitrite ions and triazenes. The latter is obviously the reaction product of the amine formed in a retro-diazotization with the diazonium ion that is still present. The yield of nitrite formed was between 0.5% (benzenediazonium ion) and 50.2% (2-nitrobenzenediazonium ion). 

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). 

Hunt, J.V., Dean, R.T. and Wolff, S. (1988). Hydroxyl radical production and autoxidative glycosylation. Glucose oxidation as the cause of protein damage in the experimental glycation model of diabetes mellitus and ageing. Biochem. J. 256, 205-212. 

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. 

Different rearrangements were observed in other cases. Thus, Maas22 reported that when photolyzed in benzene the polysilyldiazoketone 180 gave the isomeric ketene 181, the product of a Wolff rearrangement (a 1,2 carbon-to-carbon rearrangement) of the initially formed carbene 182 (Eq. 57). The isomeric bis-silylketene 183 was not observed, but the siloxa-tene 184 was also a product of the reaction. 

Wolff rearrangements were also observed when most of the same acylsi-lyldiazoalkanes were photolyzed in acetone instead of benzene.21 The ketenes 185 resulting from a 1,3-methyl migration of the silene were detected in addition to the expected ene product 186 derived from the reaction of the silene with acetone (or other enolizable ketones) (Eq. 58). When R = Ad, only the cyclic siloxatene 187 was formed under the same... 

Carboalkoxymethylenes, like acylmethylenes, undergo rearrangement to ketenes as well as the olefin addition and C—H insertion reactions characteristic of methylenes.<37> Thus the photolysis of ethyl diazoacetate in olefinic solvents leads to substantial yields of products, which can be rationalized in terms of a Wolff rearrangement of the carboethoxymethylene followed by cycloaddition of the resulting ethoxyketene to the olefin ... 

Thermolysis of 58a in butanol affords, together with 17% of 60a (R = C4H9) which evidences the intermediacy of the thiophosphene 59 a, a variety of partly atypical products which seriously impede the desired rearrangement38. Photolysis of 58b in methanol is also found to give only 18 % 1,2-P/C shift to form the heterocumulene 59b, from which the thiophosphinic rater 60b (R = CH3) results 39). As already mentioned in connection with the photolysis of diazo compounds of type 36 (see Sect. 2.2), Wolff rearrangement (9%) and O/H insertion (6%) once again compete with thiophosphinic ester formation. Moreover, solvolysis of the P(S)/C(N2) bond 391 prevents a greater contribution of carbene products to the overall yield. 

Products of a so-called vinylogous Wolff rearrangement (see Sect. 9) rather than products of intramolecular cyclopropanation are generally obtained from P,y-unsaturated diazoketones I93), the formation of tricyclo[2,1.0.02 5]pentan-3-ones from 2-diazo-l-(cyclopropene-3-yl)-l-ethanones being a notable exception (see Table 10 and reference 12)). The use of Cu(OTf), does not change this situation for diazoketone 185 in the presence of an alcoholl93). With Cu(OTf)2 in nitromethane, on the other hand, A3-hydrinden-2-one 186 is formed 160). As 186 also results from the BF3 Et20-catalyzed reaction in similar yield, proton catalysis in the Cu(OTf)2-catalyzed reaction cannot be excluded, but electrophilic attack of the metal carbene on the double bond (Scheme 26) is also possible. That Rh2(OAc)4 is less efficient for the production of 186, would support the latter explanation, as the rhodium carbenes rank as less electrophilic than copper carbenes. 

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