Olefin light-induced

One example of selective photochemistry with lasers is the gasphase photochemical addition of bromine to olefin molecules induced by the monochromatic light near 6940 A from a pulsed, tunable ruby laser, as studied by Tiffany... 

Lack of stereospecificity, extensive formation of olefinic products, and extensive tar formation limit the thermal decomposition of pyrazolines as a route to cyclopropanes.182 263 Light-induced decomposition of stereoisomeric pyrazolines establishes a method for the formation of cyclopropanes stereospecifically.222 Photolysis of 3-carbomethoxy-cis-3,4-dimethyl-l-pyrazoline (CCLI) produced cis-l,2-dimethylcycIopropane-l-carboxylate (CCLII) and without olefinic formation. Furthermore, irradiation of 3-carbomethoxy-trans-3,4-dimethyl-l-pyrazoline (CCLIII) gave [Pg.123]

The initiation step in this reaction does not necessarily involve excitation of the a,p-unsaturated ester, since carbamoyl radicals may be produced by other processes, as in the case of the isolated double bond. The chemical yield of this direct light-induced addition reaction was somewhat higher than the one obtained in the terminal olefins case. It may be assumed that the radical resulting from the addition of a carbamoyl radical to the a,(Tunsaturated system... 

The products of this photoalkylation reaction are 3-alkylated-2-pyrro-lidones and 5-alkylated-2-pyrrolidones (1 2). It is noteworthy that in this reaction the alkylation at the carbon alpha to the nitrogen atom is the predominating reaction, whereas the alkylation at the carbon alpha to the carbonyl yields the minor product of the reaction. Similar results have been obtained in the thermal process (48). The light-induced addition of 2-pyrrolidone to olefins when induced directly leads to traces only of the desired 1 1 adducts. However, the use of acetone as a photosensitizer enables this reaction to proceed in relatively high yields. 

The light-induced addition of 2-pyrrolidone to olefins when induced directly by light leads to traces only of the desired 1 1 adducts. On the other hand, when acetone is used as a photosensitizer for this reaction it results in relatively high yields of the 1 1 adducts and may be exploited for synthetic purposes in some cases. As in the case of y-butyrolactone the initiation step can be regarded involving a hydrogen atom abstraction process from the lactam by the excited acetone molecule,... 

The Light-induced Addition of y-Butyrolactone to Olefins. Chem. 

The attempted synthesis of [njcyclophenacenes has also been reported. Kuwata-ni and coworkers reported the synthesis of a pentabenzo[20]annulene, as a possible precursor to [10]cyclophenacene (Scheme 2.3) [16]. Light-induced electrocycli-zation of the precursor was unsuccessful because of isomerization of the (Z)-olefin into the (E)-olefin, which undergoes an undesirable transannular reaction [17]. St. Martin and Scott tried to synthesize [12]cyclophenacene, but attempts at the macrocyclic oligomerization of substituted naphthalene and phenanthrene building blocks by flash vacuum pyrolysis method were unsuccessful [18]. 

The reaction is not accompanied by the insertion of methylene groups into the C—H bond attached to the olefinic linkage 457). The latter is a serious side reaction in the light-induced methylenation of olefins by diazomethane, giving inseparable isomeric hydrocarbons along with the desired cyclopropane derivatives 23, 119, 387, 465, 554). Isomerization of the olefin is not observed and no rearranged cyclopropane derivatives are produced 457). 

Chloro(methoxy)- and chloro(phenoxy)carbenes, which are generated from the diazirine precursors, behave as ambiphiles in additions to alkenes, exhibiting high reactivities toward both electron-poor and electron-rich olefins. Methoxy(phenyl)- and ferrocenyl(methoxy)methylenes have been transferred in a stereospecific manner from transition metal complexes of these species to electron-deficient alkenes. Irradiation of benzocyclobutanedione with UV light induces a rearrangement of the cyclic a-diketone to 17, which has been trapped by alkenes in good yields " . Thermolysis of 18 gives rise to nucleophilic dimethoxycarbene, which has been intercepted by electron-deficient olefins or by styrene derivatives. 

Irradiation of propylene and 02-loaded zeolite BaY at room temperature with green or blue light induced partial oxidation of the olefin [18]. Readily identified products were acrolein, allyl hydroperoxide, and propylene oxide. The hydroperoxide was found to be stable when the zeolite was kept at -100°C. Hence, photolysis experiments at this temperature allowed us to find out about the origin of the aldehyde and epoxide. Allyl hydroperoxide was the main product at -100°C, the remaining 13% were propylene oxide. Warm-up of the zeolite after photo-accumulation of the hydroperoxide produced propylene oxide if excess propylene was kept in the matrix, but only acrolein if the olefin was removed prior to warm-up. Hence, allyl... 

Elad, D., and R. D. Youssefyeh The Light-induced Addition of y-Butyrolactone to Olefins. Chem. Commun. 7 (1965). 

The 1,3-cycloaddition of ethylenes to benzene and its derivatives, giving rise to dihydrosemibullvalenes, has been known for a number of years and the reaction has recently been reviewed.84 The reaction with cyclopentene as olefin has been the subject of several earlier reports.10 Its light-induced addition to anisole can be used as a stereospecific synthesis of perhydroazulenes 35 the adduct (18) is formed in 85% yield. Its consumption of only one mole of hydrogen on catalytic hydrogenation and its failure to undergo photosensitized decomposition have been... 

Some 30 years after Bresler, Beredjick reported the details of an ultraviolet (UV) light-induced 2-D polymerization at the air/water interface. Oligomeric components were used as monomers which had been prepared from dodecenyl succinic anhydride, maleic anhydride and propylene glycol by solution condensation, such that each oligomer on average carried 1.5 olefinic units. These monomers were then transferred to the air/water interface and crosslinked by radical polymerization. Unfortunately, very litde proof was provided regarding the achievement of a 2-D crosslinked polymer [71]. 

Scheme 4.9 Rh(lll)-catalyzed orfho-directed olefination of arylsilanes, followed by light induced intramolecular cyclization to indanone derivatives as reported by Bolm and coworkers [56].

Simple homolysis of the C-I bond by heating or by light is the most straightforward approach and was the first used for adding perfluoroalkyl iodides to olefins. One presumes that both the thermal and the photochemically induced addition reactions of perfluoroalkyl radicals proceed via free radical chain reactions as depicted in the Scheme below. However, the conditions of these reactions are rarely ideal for preparative purposes because high temperatures are required for the thermolytic process and long photolysis times are required for the photolytic method [60]. 

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