Wolff photolytic

D. Cyclic a-Diazoketones Ring-Contraction in Photolytic Wolff Rearrangements... 

The photolytic decomposition of a-diazoketones, accompanied by rearrangement to ketene (photolytic Wolff rearrangement), has been used successfully in the preparation of A-nor- and C-norsteroids. The method is reviewed in chapter 15 by R. M. Scribner. ... 

In this section we first discuss photolytic reactions of arenediazonium salts and report on quinone diazides at the end of the section in the context of imaging technology. Diazoalkenes, non-quinonoid diazo ketones, and the Wolff rearrangement are treated in the book on aliphatic diazo compounds (Zollinger, 1995, Chap. 8). 

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). 

Scheme 10.14 gives some other examples of Wolff rearrangement reactions. Entries 1 and 2 are reactions carried out under the classical silver ion catalysis conditions. Entry 3 is an example of a thermolysis. Entries 4 to 7 are ring contractions done under photolytic conditions. Entry 8, done using a silver catalyst, was a step in the synthesis of macbecin, an antitumor antibiotic. Entry 9, a step in the synthesis of a drug candidate, illustrates direct formation of an amide by trapping the ketene intermediate with an amine. 

The formal relationship between cyclopropenone and an a,a -biscarbene of a ketone (R—C—CO—C—R ) initiated investigations on photolytic and Ag-catalyzed decomposition of a, a -bisdiazo dibenzyl ketone (49) (Trost50 ). Indeed, diphenyl-cyclopropenone was formed in addition to other products (52 and tolane) derived from it furthermore, products resulting from solvent insertion and Wolff rearrangement of the monocarbene 50 were isolated (51) ... 

Other synthetic routes to the carbapenem ring system include photolytic Wolff rearrangement (73JCS(P 1)2024), aldol condensation (78JA313), addition-cyclization (80JOC1135) and /3-lactam formation (78JOC4438,79TL4359). An excellent review of carbapenem synthesis has recently appeared (82H(17)463). 

The photolytic Wolff ring contraction of diazopyridones (181) is a synthesis of pyrrole-2-carboxylic acids via carbene (182) and ketene (183) intermediates (76S754). 

The photolytic Wolff ring contraction of diazopyridones 247 leads to pyrrole-2-carboxylic acids 250 via carbene 248 and ketene 249 intermediates <1976S754>. The thermolysis of 2-azidopyridine A-oxides 251 affords A-hydroxy-2-cyano-pyrroles 252 (Scheme 137) <1973JOC173> (see also Section 3.4.3.11). 

Another synthetic route to )8-lactams involves the photolytic ring contraction of 4-diazopyrrolidine-2,3-diones. Diazo compounds 49 undergo Wolff... 

The intramolecular insertion into the N—H bond of j8-lactams was used successfully in the synthesis of bicyclic ring systems. Photochemical, in contrast to Rh(II)-catalyzed, decomposition of diazo ester 62 was found to occur far less selectively. In the photolytic reaction, the imide 63 is the major product. It presumably arises by a photolytic Wolff rearrangement to a ketene intermediate, which is trapped intramolecularly. With Rh2(AcO)4 catalyst the Wolff rearrangement is suppressed and 62 undergoes ring closure to 64 nearly quantitatively (80TL31). 

A wide variety of fused cyclopropanes featuring a carbonyl group can be obtained in good yield from a-diazo- -carbonylphosphoryl derivatives (Table 4). It is worthy of note that only the copper powder catalyzed method yields the expected cyclopropanes under photolytic conditions, Wolff rearrangements are observed. ... 

Flash photolytic Wolff rearrangement of a-cyanodiazoacetophenone (210) produces a-cyano-a-phenylacetic acid (211) via hydration of the ketene intermediate.89... 

Examples of analogous [2 +2] cycloadditions of ketenes with alkenes in photolytic Wolff rearrangements have been known since 1964 (Masamune and Castellucci see references given by Danheiser et al., 1990b, footnote 11). 

Wolff s discovery in 1902-1912 was accomplished by using thermal and silver-catalyzed conditions. Photochemical Wolff rearrangements were discovered only 50 years later (Horner and Spietschka, 1952). During the last 40 years, more preparative and mechanistic work was made under photolytic conditions. Nevertheless, we will discuss first mechanistic investigations of the thermal method. 

For the investigation of the migratory tendency of groups in Wolff rearrangements, the results obtained with unsymmetrically substituted 2-diazo-l,3-dicarbonyl compounds (8.89) are interesting (8-45). Systematic investigations under comparable thermal and photolytic conditions had already been made at an early time (see review of Meier and Zeller, 1975, Table 2), more recently by Tomioka et al. (1983), by Nikolaev et al. (1991, and earlier references mentioned there), by Nikolaev and Popik (1992), Meier et al. (1988), McMahon et al. (1985), and by others. 

Photolytic or Rh-catalysed decomposition of (l-diazo-2-oxoalkyl)phosphonic amides (372) leads to the pho.sphinylphenylacetic acid (374)(presumably by way of a Wolff rearrangement to (373) after initial carbene formation) and to 1,2-azaphosphetidines (375). the latter being formed diastereoselectively in favour (10 1) of the (Xp) form. ... 

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