A-diazoketone photolysis

Second Encounter with Versatile a-Diazoketones Photolysis versus Reaction with Methanol... 

Bachmann, C., N Guessan, T. Y., Debu, F., Monnier, M., Pourcin, J., Aycard, J. P., Bodot, H. Oxirenes and ketocarbenes from a-diazoketone photolysis experiments in rare gas matrices. Relative stabilities and isomerization barriers from MNDOC-BWEN calculations. 

Photolysis of a-diazoketones has also been used to prepare A-norsteroids. Results in the A-nor series support the ketene intermediate invoked for the assignment of the 16) -configuration to the D-nor acids. Thus, irradiation of 2-diazo-5a-cholestan-3-one (99) gives 2/ -carboxy-A-nor-cholestane (100, R = H) in 45 % yield. ... 

The photolysis of cyclic a-diazoketones results in ring contraction to a ketene, which can be isolated as the corresponding ester. 

This type of reaction is better demonstrated by two examples in which the insertion reaction is a bit more obvious when there are no p hydrogens, the carbene inserts into C-H bonds a little further away in the same molecule or even in the solvent (cyclohexane in the second example). In the first case, the carbene is formed by a elimination and, in the second case, by photolysis of a diazoketone. 

A total synthesis of ( )-royleanone from 5,7,8-trimethoxy-l-tetralone (123) has been described.129 The tetralone was converted into the tricyclic ketone (124), which was in turn converted into 11,12,14-trimethoxypodocarpatriene (125). Demethyla-tion and oxidation afforded the quinone (126 R = H) which was alkylated to give royleanone (126 R = Pr ). Synthetic studies in the resin acid series have led130 to the preparation of the dicarboxylic acid (127) with a cis a/b ring junction. The preparation of some tetracyclic ketones as intermediates for gibberellin synthesis has been described.131 132 The key reaction involves photolysis of a diazoketone (128) to afford the tetracyclic system (129). In a synthesis of phyllocladene from abietic acid... 

Cyclization of /3-mercaptoaldehydes has been reported to give 2-hydroxy-thietanes (which are thioacetals) in 16-84% yield.They are said to be useful as flavoring substances. However, cyclization of 4-mercaptopropene gave only 0.1% of 2-methylthietane. The major product was thiolane. Photolysis of the a-diazoketone of 2,2,5,5-tetramethylthiolane-3,4-dione in methanol gave a 28% yield of 2,2,4,4-tetramethyl-3-carbomethoxythietane. " Several dispirothietanes have been obtained from the bis-hydrazone of 3-thietanone. ... 

Photolysis of l,3-dithian-5-ones, for example, 360, and 3-methyl-5-thiacyclo-hex-2-ene-l-one, 361, gives 3-thietanones. A 3-thietanone intermediate was suggested in the photolysis of 3-thiatetralone. Photolysis of 8-thiabicyclo-[3.2.1.]-3-octene-2,6-dione gives a 3-thietanone, 8-thiabicyclo[4.1.1]-4-octene-3,7-dione. Thermolysis of the a-diazoketone 362 gives the 2-exomethylene derivative 363. ... 

Photolysis of disilanyl a-diazoketones 497 leads through the sequence involving silyl carbene formation followed by rearrangement to acyl sil-enes and their facile cyclization to give l-oxa-2-sila-3-cyclobutenes 498 (84JA1486 88CC72 90CB589). 

The singlet form of carbenes substituted with a carbonyl group is much lower in energy than the triplet, so the photolysis of a-diazocarbonyl compounds gives singlet carbenes. The photo-Wolff rearrangement (Chapter 2) of a-diazoketones occurs upon photolysis of these compounds. 

Diphenylpyridazine N-oxide is transformed upon irradiation into a mixture of 3-benzoyl-5-phenylpyrazole (307) and 2,5-diphenylfuran (308). A diazoketone (306) is proposed as intermediate for both products. In a low-energy photolysis experiment it was shown that the diazoketone reaches a maximum concentration after 20 /xsec, and in a nanosecond photolysis the diazoketone is formed as the primary photoproduct in less than 20 nsec. The diazoketone is able to decompose competitively by thermal (to 307) and photochemical (to 308) pathways. Similarly, irradiation of 3,4,5,6-tetraphenylpyridazine N-oxide results in the formation of a mixture of tetraphenylpyridazine (61) and a bicyclo-heptadienone (309) as the main products, together with compounds 310-312 7,598 an intermediate diazoketone (cf. 306) is proposed (Scheme 18). 3,4,6-Triphenylpyridazine 1-oxide gives upon irradiation almost equal... 

Much remains to be understood about the photochemical behaviour of formaldehyde and related species despite further work published this year. For example, the question of the possible formation of the isomeric hydroxycarbene (CHOH) remains unresolved. The following tautomeric equilibrium between singlet a-oxocarbenes (1) formed by photolysis of the corresponding a-diazoketones (2, R = Me, Et, Pr ) has been reported by Tomioka et al. 

Photolysis of a-diazoketones produces acyl carbenes, which efficiently rearrange to ke-tenes that are subsequently trapped (Eq. 16.73). This photochemical version of the Wolff re-... 

The most extensive application of a-diazocarbonyl compounds is in the lithographic production of integrated circuits used by the computer industry. The majority of photoresist materials involved in this process are a-diazoketone derivatives. 2 Upon photolysis, these compounds form ketenes that subsequently react with water to produce carboxyhc acids. The difference in carboxylic acid and diazoketone solubility is then utilized to pattern electronic devices. 

During 1961-2 four independent groups almost simultaneously reported the first syntheses of D-norsteroids, based on the photolysis of 16-diazo-17-ketones. In a typical procedure. Cava and Moroz ° convert the 16-oximino-17-one (93) derived from estrone methyl ether (92) to the diazoketone (94)... 

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