Mercury lamps alkyl benzenes with

A new synthetic route to alkyl-substituted quinones has relied on the photochemical reaction of 2,3-dichloro-l,4-naphthoquinone with a thiophene derivative (77CL851). Irradiation of a benzene solution of the quinone and thiophene by a high pressure mercury lamp gave photoadduct (295) in 56% yield. Desulfurization of this compound over Raney nickel (W-7) gave the 2-butyl-1,4-naphthoquinone derivative (296 Scheme 62). Alkyl-substituted quinones such as coenzyme Q and vitamin K, compounds of important biological activity, could possibly be prepared through such methodology. 

Irradiation with a mercury lamp of (diacyloxyiodo)benzene (64) in the presence of disulfide, generates the corresponding alkyl sulfide (65) together with iodobenzene and carbon dioxide (eq. 2.31) [75, 76]. This is useful for the preparation of adamantyl sulfides or selenides, since the preparation of such caged tert-alkyl sulfides or selenide is not so easy with polar reaction methods. 

Generally, the reactions are carried out in refluxing benzene solution, since the yield in benzene is better than that in other solvents. Probably, the radicals formed may be somewhat stabilized by the weak orbital-orbital interaction between the radicals and benzene. However, from the environmental point of view, toluene or dioxane is recently used. As substrates, alkyl bromides or alkyl iodides are used, and the reactivity increases in the order prim-alkyl < seoalkyl < te/t-alkyl. Sugar anomeric bromide (3) is generally not so stable, so the reaction is carried out under irradiation conditions with a mercury lamp at room temperature (eqs. 4.2 and 4.3). There are two types of anomeric glycosyl radicals as shown in Figure 4.1. One is the axial radical [I], and the other is the equatorial radical [I ]. The axial radical is more nucleophilic than the equatorial radical due to the stereoelectronic effect, where this effect comes... 

The most well-known radical allylation reagent is allyltributyltin. Typical radical allylations are carried out by the irradiation of a benzene solution of alkyl bromide or selenide and allyltributyltin in the presence of AIBN with a mercury lamp. Eqs. 4.32a and 4.32b show the allylation of a-bromosulfone (76) and a-phenylselenyl-cyclopentanone... 

Finally, as examples of similar types of reactions, photolytic treatment of O-acyl ester (D) of benzophenone oxime, A-acyloxy-phthalimide (E), and O-acyl ester (F) of A-hydroxy-2-pyridone with a mercury lamp generates the corresponding alkyl radicals via decarboxylation. However, these reactions can be used only for the alkylation of aromatics (solvents such as benzene) and reduction [86-89], so their synthetic utility is extremely limited. 

Saccharin 218 is obtained by KMn04 oxidation of o-methylbenzenesulfonamide 217 (Scheme 126). Various V-alkylsaccharins 219 (n = 2) and A-alkyl-l,2-benzisothiazolin-3-one A-oxides 219 (n= 1) are conveniently prepared in moderate to good yields by the reaction of A-alkyl(0-methylarene)sulfonamides with (diacetoxyiodo)benzene in the presence of iodine under irradiation with a tungsten or mercury lamp <1999T14885, CHEC-III(4.05.9.1.2)599>. 

Miranda etaL reported that irradiation (254-nm mercury lamp) of [3.2]PCP-2-one 16 in benzene led to [2.2] PCP 15 as the only product via acyl-alkyl biradical 32 and biradical 33. A laser-flash photolysis study (266 nm) of 16 in cyclohexane indicated that biradical 33 is detectable at room temperature and does not cleave to p-xylylene 35 but cycKzes to [2.2]PCP 15 or dimerizes to [2 ]PCP 34. Irradiation (laser, 308 nm) of a cyclohexane solution of 15 containing a triplet quencher (cyclooctadiene) showed two absorption maxima, which correspond to p-xylylene 35 and the hiradical 33. The cyclophanes [2 ]PCP 21 and [2 ]PCP 34 were formed by irradiation (laser, 248 or 266 nm) of cyclohexane solutions of [2.2]PCP 15. While the formation of 34 agrees well with the intermediacy of 33, the detection of [2 ] PCP 21 provided further evidence for the intermediacy of p-xylylene 35, which can couple either its tiimeric or tetrameric products. 

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