Reactions of 1,4-Diketones

2 Reactions of 1,3-Diketones. - ab initio Calculations have been carried out in a study of the single bond rotation within 3-hydroxyacrolein. Pulsed-laser photolyis of acetylacetone, in its enol form, shows that hydroxyl radicals are formed. The photochemical reactivity of some 1-acetonaphthones in the presence of piperidinopropenenitrile has shown both addition and substitution reactions. Photochemical ring expansion of ethyl 2,4-dioxo-3-(aryl)-aza-bicyclo[3.1.0]hexane-6-carboxylates afford ethyl N-(aryl)-2,6-dioxo-piperid-3-ene-4-carboxylates in 68-80% yields.  

2 Reactions of 1,3-Diketones - The carboximide derivative (203) undergoes photochemical rearrangement on irradiation in acetonitrile using Pyrex filtered light. The reaction is considered to proceed by a zwitterionic intermediate such as (204). When the reaction is carried out in the presence of P-ketoesters [e.g. (205)] with added triethylamine, adducts are formed in yields of 40-60% and have been identified as (206). The intermediacy of (204) is supported by the formation of (207). 

3-diketones (208) isomerise on irradiation at 300 nm in benzene solution. The products are the lactones (209) and they are formed in high yield as a mixture of the two possible isomers (209a) and (209b). The reactions are proposed to occur from a short-lived singlet state since sensitisation was ineffective. When acetophenone was used as a sensitiser the dione (208d) did 

1 Reactions of 1,2-Diketones - A study of the ketoamides (217) has shown that their direct irradiation in benzene solution brings about efficient cycloaddition to give the bicyclic oxetanes (218). In the solid state, irradiation of (217) also affords these products. However, the syn anti ratio is higher in the solid state than in solution. Furthermore, there is a temperature effect and the syn. anti ratio is greater at lower temperatures. The ee is also affected by changes of temperature. 

High chemical but low quantum yields of the two products (233) and (234) are obtained on irradiation (X 500 nm) of the tetraketones (235). The primary photochemical step is the conversion of the tetraketones into carbon monoxide and the ketenes (236). The reaction process occurs from the singlet state and is thought to be concerted. The final products are formed by the addition of these ketenes (236) to ground state tetraketone. The ketene (236b) was studied in a little more detail and it was shown that irradiation in benzene or toluene at room temperature results in the formation of the dimer (237). Addition of the same ketene to diketones such as biacetyl was also reported. 

2 Reactions of 1,3-Diketones. - A tuneable laser has been used to study the photoisomerization of acetylacetone in a nitrogen matrix at 10 Organero and Douhal have reported a temperature effect on non-radiative decay 

The photochemical reactions of ethyl phenylglyoxalate (217) in benzene have been re-examined. The three new products (218), (219) and (220) have been isolated from the reaction mixture. The quantum yields for the formation of the products are dependent on concentration. Irradiation of the phenylglyoxalate derivatives (221) results in conversion into the lactones (222) from (221, R = H) and (223) and (224) from (221, R = Me). The reactions are proposed to involve an intramolecular electron transfer process forming a zwitterionic biradical. This leads to activation of the methylenes adjacent to the sulfur atom. A similar effect is observed with the nitrogen analogue (225) which affords (226) as the 

The cycloaddition of the diene (234) to the furan-2,3-dione derivatives (235) affords the cycloadducts (236). The reaction takes place efficiently with high regio- and stereo-selectivity. 

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A different kind of triazine, 3,5,6-trisubstituted 1,2,4-triazines 166, were prepared by reaction of 1,2-diketones 164 with acyl hydrazide in the presence of ammonium acetate and acetic acid at 180 °C for 5 min under microwave irradiation in a sealed tube [107]. Different substituents can be introduced in the final triazines providing a general approach for this kind of heterocycles (Scheme 59). 

Cyclic peroxides are obtained from diketones when a five- or six-membered peroxide ring can be formed, as is the case with acetyl-acetone, acetonylacetone, triacetylmethane, and benzalacetylace-tone. In the reaction of 1,2-diketones with hydrogen peroxide, the C—C bond is broken to give carboxylic acids, without intermediate formation of a four-membered peroxide ring.37... 

Taylor, R.J.K., Bii-Wittig reactions of 1,2-diketones. The preparation of 3,4-disubstituted mucononi-trUes, Synthesis, 566, 1977. 

Reactions of 1,2-Diketones and other 1,2-Dicarbonyl Compounds. - Further details of the control of the photocyclizations of enamides such as (142) affording (143) have been described. The results obtained are influenced by the nature of the chiral auxiliaries used. The best results are obtained using ionic and covalent auxiliaries in the crystalline phase or in zeolites. " Photochemically induced a-cleavage occurs on irradiation of the ketoamides (144) in water. This results in the release of the carboxylic acid moiety. The by-product of the reaction is the hemiacetal (145). " The irradiation of propellane in the presence of... 

Reactions of 1,2-Diketones and other 1,2-Dicarbonyl Compounds. - 1,2-Dicarbonyl compounds such as glyoxal and biacetyl have been irradiated under direct sunlight. A study has examined the wavelength dependence for fission of glyoxal into the CHO radical on irradiation in the 290-420 nm range. a-Fission is the principal photochemical reaction of vicinal cyclic tricarbonyl compounds such as indanetriones. ... 

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