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Photo addition

When the substituent groups in the polyphosphazenes were azobenzene [719] or spiropyran [720] derivatives, photochromic polymers were obtained, showing reversible light-induced trans-cis isomerization or merocyanine formation, respectively. Only photocrosslinking processes by [2+2] photo-addition reactions to cyclobutane rings could be observed when the substituent groups on the phosphazene backbone were 4-hydroxycinnamates [721-723] or 4-hydroxychalcones [722-724]. [Pg.224]

Photo-addition of allene to the enone (90) yield adduct (91) in 75 % yield, which was subjected to ketalization in 77% yield. Epoxidation of (92) with perbenzoic acid followed by chromatography on alumina afforded two expoxides (93) and (94). Both (93) and (94) could be converted separately through (95) and (96) respectively which was the common intermediate leading to isoishwarane (98) and ishwarane following a deketalization-retroaldol-aldol process to furnish the keto-alcohol (97) (99) 30>. [Pg.99]

Bryce-Smith, D., and J. E. Lodge Preparation of cyclo-octatetraenes by the photo-addition of acetylenes to benzene. Proc. chem. Soc. [London] 1961, 333. [Pg.70]

Hara, M., Y. Odaira, and S. Tsutsumi Photo-addition reactions of dimethyl maleate and dimethyl acetylene dicarboxylate with norbome-ne. Tetrahedron 22, 95 (1966). [Pg.74]

Sasse, W. H. F., P. J. Collin, and G. Sugowdz The photo-addition of tolan to some naphthalenes. The formation of derivatives of 2.3-benzo-tetracyclo[3.2.1.05-7.08-8]octene-(2). Tetrahedron Letters 1965, 3373. [Pg.79]

The cyclic peroxide system was constructed by photo-addition of 02 to the diene 25 in a total synthesis of plakortic acid derivatives isolated from a marine sponge <02OL485> and the key step in a synthesis of related marine products is an intramolecular Michael addition of a peroxy hemiacetal <02BMCL69>. [Pg.376]

Dimethylhexa-2,4-diene and a 4,6-dienone undergo photo-addition to give a mixture of isomeric 4,5-adducts of type (302), including 4a,5a-, 4a ,5/3-, and 4/3,5/3-adducts. 4-Methylpenta-1,3-diene adds in the same orientation. The mechanistic and stereochemical features are discussed both dienes are of the type which function as substituted alkenes rather than as Diels-Alder dienes.242... [Pg.270]

The photo-addition of ethoxycarbonylnitrene on to unsaturated steroids and the photo-rearrangements of steroidal 4-azasteroidal 5-en-3-ones have been reviewed.248... [Pg.272]

The photolysis of the 6-oxo-3a,5a-cyclo-19-oic acid (520) gives initially the 4-en-6-one (521), but in t-butanol a rapid photo-addition then affords the 4a-t-butoxy-6-hydroxy-lactone (522). Similar reactions transformed the methyl ester (523) into the ketonic derivative (525). Photolysis of the saturated keto-acid (526), in an alcohol as solvent, gave first the corresponding 6-monoester (527) of the 5,6-seco-6,19-dioic acid, and finally the 6,19-anhydride (528). Formation of the 6-ester (527) probably involves addition of the solvent alcohol to a keten intermediate. ... [Pg.322]

The results confirm that It is the state of the arene which reacts with ground state alkene but do not allow any conclusion to be made about the intermediacy of an exciplex or any other species along the reaction path. Also in the same laboratory, the products of the meta photo-addition of cyclopentene with alkyl and alkoxy benzenes have been determined and the effect of increasing size of the alkyl or alkoxy group examined. The major product isolated is (80). although (81) and other isomers become more important for alkyl benzenes as the substituent s size is increased. The results are consistent with a polar mechanism involving the formation of (82) where the substituent stabilises the positive charge and steric interactions are avoided by the endo orientation of the cyclopentane. Also consistent with a polar intermediate are the meta adducts... [Pg.301]

Photo-addition of alkenes to A methylnaphthalene dicarboxamides in benzene has been studied. The structure of the arene moiety in the imide was important in determining the reaction path. Mainly cyclobutane and oxetan formation occurred. The dicarboximide (342) undergoes photochemical cyclization with incorporation of methanol to yield the two products (343) and (344) in 55 and 16% respectively. This type of cyclization appears to be quite general for such systems and is also reported for the imides (345) and (346). A variety of products resulting from aminolysis, reduction, and radical coupling is produced on irradiation of the phthalimide (347) in diethylamine. ... [Pg.222]

We noted that a small amount of anhydride 41 was formed in the photolysis of 32 when no added hydroxylic reactant was present. Presumably a trace of water is responsible for the small amount of fragmentation that occurred. The anhydride may arise from the photo-addition of the initially formed phosphonic acid 40 to the phosphoryl group, followed by fragmentation. [Pg.125]

The meta photo-addition of cyclic alkenes to benzene derivatives generally yields the endo stereoisomers such as (34) rather than the exo stereoisomers such as (35), even though formation of the latter would involve less steric interaction in the approach of the alkene to the arene. This preference has been attributed to a weak bonding interaction between the arene w-system and a C-H (i.e. [Pg.197]

Bryce-Smyth, D., and A. Gilbert Specificity in the Thermal- and Photo-additions... [Pg.77]

Gilbert and Rodwell have examined the photo-addition of furan to various substituted benzenes.With benzonitrile the meta adduct... [Pg.229]

The same group has investigated the photo-addition of alkenes to 1,2- and 2,3-naphthalenedicarboxylic acid anhydride.No products of addition of the alkene to the naphthalene ring were observed instead the alkene inserts into the C(=0)-0 bond of the anhydride or adds to one of the carbonyl groups to produce an oxetane. By analogy with imides, the insertion reaction can be viewed as an addition to the partial C-o double bond Illustrated by the contributing structure (81) to give adduct (82) which collapses to the isolated insertion product (83). [Pg.236]

The photo-addition of saturated heterocyclic eunines containing two heteroatoms (e.g. morpholine and piperazine) to the singlet excited state of benzene has been examined the outcome of the... [Pg.236]

Oxetans. - A mechanistic investigation of the reaction of methylthiotri-methylsilane (38) and oxetan, in the presence of a catalytic amount of zinc chloride, suggests the involvement of an oxonium cation-methylthiozinc dichloride ion-pair, resulting in the formation of (3-methylthiopropoxy)-trimethylsilane (39). A dependence of the stereochemistry of the photoaddition products of aldehydes and alkenes on the concentration of alkene has been observed.Additional examples of the known photo-addition of benzophenone to 2,5-dimethylthiophen to form an oxetan have been reported and the unusual bis(cyanomethylene)oxetan (40) has been described. ... [Pg.65]


See other pages where Photo addition is mentioned: [Pg.550]    [Pg.556]    [Pg.558]    [Pg.560]    [Pg.561]    [Pg.563]    [Pg.569]    [Pg.571]    [Pg.574]    [Pg.577]    [Pg.748]    [Pg.314]    [Pg.212]    [Pg.459]    [Pg.215]    [Pg.560]    [Pg.258]    [Pg.119]    [Pg.184]    [Pg.186]    [Pg.108]    [Pg.392]    [Pg.393]    [Pg.221]    [Pg.226]    [Pg.228]    [Pg.231]    [Pg.484]    [Pg.203]   


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