Sulfides, allyl irradiation

Nishimura and coworkers57-59 studied the y-radiolysis of aqueous solutions of sulfoxide amino acids. Sulfoxide amino acids are the precursors of the flavors of onions (S-propyl-L-cysteine sulfoxide, S-methyl-L-cysteine sulfoxide and S-(l-propenyl)-L-cysteine sulfoxide) and garlic (S-allyl-L-cysteine sulfoxide). In studies on sprout inhibition of onion by /-irradiation it was found that the characteristic flavor of onions became milder. In the y-radiolysis of an aqueous solution of S-propyl-L-cysteine sulfoxide (PCSO)57,58 they identified as the main products alanine, cysteic acid, dipropyl disulfide and dipropyl sulfide. In the radiolysis of S-allyl-L-cysteine sulfoxide (ACSO) they found that the main products are S-allyl-L-cysteine, cysteic acid, cystine, allyl alcohol, propyl allyl sulfide and diallyl sulfide. The mechanisms of formation of the products were partly elucidated by the study of the radiolysis in the presence of N20 and Br- as eaq - and OH radicals scavengers, respectively. 

A useful solution to the latter problem, introduced by Keck and Byers,141 makes possible crotylation and isoprenylation. Irradiation of an allyl sulfide (28 3 equiv.), a reactive radical precursor (29 1 equiv.) and hexabutylditin (1.5 equiv.) produces substitution products (30) in good yields (Scheme 41). The... 

When BR is irradiated in the presence of some sensitisers, such as allyl bromide or phenyl sulfide, the band at 710 cm"1 due to the cis isomer slowly weakens as the irradiation time increases. On the other hand, the intensity of the peak at 970 cm1 which is due to the trans isomer slowly increases. From an initial cis/trans ratio of 57/43, BR was isomerised with allyl bromide in nitrogen to a structure with a cis/trans ratio of 10/90. In this case the band at 1450 cm 1 which is due to CH2 bending was taken as internal reference. 

Allyl-allyl cross-coupling of allyl bromides (Structure 1) and allyl sulfides (2) carrying homoallylic alcohol or ester functions takes place under irradiation with hexamethylditin (see eq. (1)). The reaction cleanly leads to 2,6-dienes (3) and no isomerization of allylic bromides is oberserved [56]. 

Oxidations. With microwave irradiation alcohols are oxidized by t-BuOOH, allylic alcohols give epoxides. 1,4-Dihydropyridines undergo aromatization, and sulfides are converted to sulfoxides. ... 

Allyldiethylamine behaves similarly, but the yields are low since neither the starting amine nor the products are stable to the reaction conditions. For the efficiency of the cyclopropanation of the allylic systems under discussion, a comparison can be made between the triplet-sensitized photochemical reaction and the process carried out in the presence of copper or rhodium catalysts whereas with allyl halides and allyl ethers, the transition metal catalyzed reaction often produces higher yields (especially if tetraacetatodirhodium is used), the photochemical variant is the method of choice for allyl sulfides. The catalysts react with allyl sulfides (and with allyl selenides and allylamines, for that matter) exclusively via the ylide pathway (see Section 1.2.1.2.4.2.6.3.3. and Houben-Weyl, Vol. E19b, pll30). It should also be noted that the purely thermal decomposition of dimethyl diazomalonate in allyl sulfides produces no cyclopropane, but only the ylide-derived product in high yield.Very few cyclopropanes have been synthesized by photolysis of other diazocarbonyl compounds than a-diazo esters and a-diazo ketones, although this should not be impossible in several cases (e.g. a-diazo aldehydes, a-diazocarboxamides). Irradiation of a-diazo-a-(4-nitrophenyl)acetic acid in a mixture of 2-methylbut-2-ene and methanol gave mainly l-(4-nitrophenyl)-2,2,3-trimethylcyclo-propane-1-carboxylic acid (19, 71%) in addition to some O-H insertion product (10%). ... 

However, the addition occurs contrary to the Markovnikov rule under irradiation by ultraviolet light or in the presence of peroxides 1 for instance, allyl-amine hydrochloride or a derivative thereof in alcoholic solution is thiolated by an excess of hydrogen sulfide under UV-irradiation, exclusively (yields up to 57%), to give 3-aminoalkanethiols.2 Addition of hydrogen sulfide is of use in the laboratory only when the reaction can be carried out in the liquid phase and is then preferably effected under the influence of a basic catalyst Dahl-bom,3 for instance, obtained 3-mefcapto-butyric acid from crotonic acid hydrogen sulfide in the presence of diethylamine in a closed vessel at 70° and 4-mercapto-4-methyl-2-pentanone is obtained in 80% yield from mesityl oxide and hydrogen sulfide with triethylamine as catalyst.4... 

Keck and Byers introduced a protocol in which the allyl sulfide was used together with (Bu Sn), when thiyl radical is unable to propagate the chain [87]. Two examples are reported below (equations (41) and (42)), in which an alkyl iodide and phenylselenide were treated with two equivalents of an appropriate sulfide and one equivalent of hexabutylditin under sunlamp irradiation [87, 88]. 

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