Addition cyclo, photo

ROMP and PROMP are very useful methods to synthesize a number of novel materials with unique properties. Poly(cyclooctenes), poly(norbornenes) and poly(acetylenes) were discussed in more details and some of their properties like Tg, cristallinity, oxygen permeability, dielectric properties etc. listed. The polymerization of the cycloolefins was done either thermally or photochemically with the "old" Ru(II)-salts and the later developed Ru-phosphines as catalysts, whereas substituted acetylenes were photo-polymerized with W-, Mo- and Ta-catalysts. In addition, polymeranalogous transformations of the double bonds in ROMP polymers, (additions and cyclo-additions, epoxidation, (photo) crosslinking etc.) were discussed. We are convinced that these materials and systems will find useful applications in the near future. 

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. 

Muller, F. and Mattay J. (1993) Photo-cyclo-additions control by energy and electron transfer. Chemical Reviews, 93, 99-117. 

Natural sunlight induced photooxidation of naphthalene in aqueous solution has also been reported by McConkey et al. to produce six major products including 1-naphthol, coumarin, and two hydroxyquinone [9]. The authors proposed that the initially formed 2 + 2 and 2 + 4 photo cyclo addition products undergo subsequent oxidation and/or rearrangement to form the observed products [9]. Grabner et al. have studied solvent effects on the photophysics of naphthalene and report that fluorescence lifetime decreases by a factor of 2.5 in aqueous solution compared to organic solvents (e.g. ethanol, hexane, acetonitrile) [10]. Based on the observed differences in naphthalene excited triplet state properties in aqueous and organic media, the decrease... 

In the course of a study of the scope of photo-1,3-additions of aromatics to olefins, Srinivasan and co-workers examined the reaction of tetralin with cyclo-pentene and observed the formation of adduct 316 21 When treated with a catalytic quantity of hydrogen chloride, 316 was rapidly isomerized to 317, an annulated tricyclo[6.3.0.03,7]undecadiene structure. 

Photolysis of an ethereal solution of photo-a-pyrone (157) and cyclopentadienyldicarbonylcobalt yields, in addition to the air-stable, yellow crystalline (cyelobutadienc)cyclo])entadienylcobalt, a dark green, air-sensitive crystalline species melting at 121° 122°C with the empirical... 

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. ... 

An approach very closely related to that of Woodward and Hoffmann is the so-called Hiickel-Mobius approach 35> based on the rule An +2 electron systems prefer Hiickel geometries and An electron systems prefer Mobius geometries 36>. When no symmetry exists and there is no cyclic orbital array the allowedness or forbiddenness of a reaction can be determined by following the form of the MO s during the reaction 37>. A detailed quantum mechanical study of the stereochemistry of thermal and photo cyclo-addition reactions has been reported38), and a quantum mechanical discussion of the applicability of the Woodward-Hoffmann rules can be found in a paper by George and Ross 39>. 

An analogous photo-isomer of A -benzyloxycarbonylmethyl-2(l//)-pyridone has been prepared and various transformations of its cyclobutene ring have been explored. The photodimerization of A -methyl-2(l/ )-pyridone in water gives exclusively the products of [4 + 4] addition the yields of trans-anti- (31), trans-syn-, cis-anti-, and cw-jjfn-dimers were 51, 0.6, 11.2, and 6.8%, respectively. In non-aqueous solvents (ethanol or benzene), only a t/-dimers were formed. The thermal cycloaddition of dimethyl acetylenedicarboxylate to 2(l/f)-pyridones also occurs across positions 3 and 6. Reaction is favoured where steric buttressing of the methyl groups in the starting pyridone occurs for example, the cyclo-adduct (32) is... 

Presumably the adducts are formed by singlet addition yielding (257) followed by a second addition. [2 + 4]Addition is also encountered yielding the photo-chemically labile 2,3-diphenylnorbornadiene. The irradiation (206 nm, pentane solution, degassed) of cyclo-octa-l,5-diyne at room temperature rapidly gave butatriene as the only product.176... 

The photoenolization of the quinone (286) can be carried by irradiation at 313 or 365 nm in acid solution. The steady state irradiation has identified the product as the unstable hydroxylated compound (287) which is formed via the enol (288). The presence of this intermediate was detected in a laser flash study of the reaction. The quinones (289) undergo cyclization when irradiated with visible light.The mechanism by which the compounds (289) are transformed into the derivatives (290) involves the production of an excited state that is either a zwitterion or a biradical. After the transfer of a hydrogen the intermediate (291) is formed. It is within this species that cyclization occurs to give the final products. (2+2)-Cyclo-adducts such as (292) and oxetanes can be obtained by the photochemical addition of quinones to homobenzvalene. Interest in the photo-SET in quinone systems has led to the synthesis of the pyropheophytin substituted naphthoquinone dyads (293). A pulse radiolysis study of vitamin K in solution has been reported. 

Irradiation of solutions of cycloheptatrieneiron tricarbonyl at low temperatures followed by addition of diphenylacetylene produces the [2 + 6] adduct, 7,8-diphenyl-bicyclo[4,2,l]octa-2,4,7-triene similar results were obtained with cyclo-octatetraene-iron tricarbonyl and related compounds. The mechanism suggested involved photo-induced replacement of one of the olefin bonds or carbon monoxide ligands in the complexes by a solvent molecule, thermal replacement of the solvent by the acetylene, and an intramolecular cycloaddition. ... 

The course of the intramolecular photocycloadditions of the isoelectronic ketene and allene of structure (372 X = O or CH2) is quite different the ketene cyclizes to (373), whereas the allene gives (374). Similar behaviour is found for other cyclo-hexenones, and opposite charge distribution in the ground states of the allenes and ketenes is thought to be responsible for the differences in regioselectivity. Deuteriumlabelling studies show that the isomerization of the benzobarrelene (375) into the benzocyclo-octatetraene (376) occurs by way of initial [2 + 2] photo-addition between the aliphatic C=C bonds. This is not the pathway favoured by previous investigators or by the Epiotis polar pericyclic theory. The photochemical addition... 

Although photo-cycloadditions to benzene are well established, analogous reactions with pyridine, which, unlike benzene, has a non-bonding HOMO, are scarce. However, photoelectron spectroscopy shows that for perfluoropyridine the HOMO is rr-bonding, and that cyclo-adducts are to be expected. In fact, pentafluoropyridine undergoes photo-addition with ethylene to give a mixture of the 1 1 and 1 2 adducts (31) and (32). ... 

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