Butadiene, direct irradiation products

Attempts to sensitize this reaction resulted in no product formation, suggesting participation of a benzene singlet in the direct photolysis. Irradiation of isoprene in excess benzene resulted in products similar to those observed with butadiene/7 Irradiation of toluene and o- and p-xylene in the presence of isoprene yielded products similar to (62).<72)... 

The reactions of butadiene are very typical. As indicated in Scheme 32, direct irradiation yields predominantly cyclobutene in the presence of Cu(I) or Hg, however, bicyclobutane formed by an x[2 + 2] process is the major product, with minor products formed through [2 + 2] cycloaddition. (Cf. Section 7.4.2.)... 

When dilute solutions of polyalkylated, sterically congested butadienes 1 in inert solvents (pentane, cyclohexane) are subjected to direct irradiation (450-W, high-pressure Hg lamp) at ambient temperature, the corresponding bicyclobutanes 2 are formed in moderate to good yield, sometimes as the only isomerization product. ... 

Reviews of the hula-twist photoisomerization of dienes have been published. New calculations dealing with the isomerism of -cw-butadiene have been reported.Molecular dynamic simulations of the photochemical behaviour of butadiene have shown that cis-trans isomerism occurs. The regioselectivity observed in the photochemical isomerism of trans,trans-l-fluorohexa-2,4-diene is proposed as due to electrostatic control. Direct irradiation of the fluorinated dienes (102) results in preferential conversion to the Z,3E isomers (103). DCA-sensitized irradiation of the butatrienes (104) in various alcohols afford the adducts (105). The simpler alcohols give moderate yields of product, while -butanol affords only a trace of the adduct. ... 

Cyclic dienes such as cyclooctadiene 7, where r-cis-conformation is dominant, undergo electrocycUzation to give the dominant products. Similarly, acyclic conjugated diene such as 2,3-dimethyl-l,3-butadiene 8 undergoes electrocycUzation on direct irradiation from the r-c/r-diene conformation preferentially [16]. 

Methylfuran, irradiated in the presence of mercury vapor, gave carbon monoxide and a fraction containing 1,3-butadiene and 3-methylcyclopropene (45 55) (67JA1758). Subsequently, it was found that in both sensitized and direct photolysis of 2-methylfuran a more complex mixture of products was obtained, where 3-methylfuran was present (Scheme 5) (68JA2720 70JPC574). 3-Methylfuran was the only product when 2-methylfuran was irradiated in diethyl ether (68JA2720). 

The photolysis of phenylethynylpentamethyldisilane (56) takes place simultaneously by at least two different processes. The main route proceeds through a silacyclopropene and the other involves transient formation of a silapropadiene. Irradiation of a benzene solution of 56 in the presence of acetone gives four products, 2,2,5,5-tetrameth-yl-3-trimethylsilyl-4-phenyl-l-oxa-2-silacyclo-3-pentene (57), 2,2,5,5-tetra-methyl-3-phenyl-4-trimethylsilyl- l-oxa-2-silacyclo-3-pentene (58), phen-yltrimethylsilylacetylene, and 1-pheny 1-1 -trimethylsily 1-3-methyl-1,2-butadiene (59), in 51,2,10, and 5% yield, respectively, with 81% conversion, of the starting disilane. The formation of 57 and 58 can be explained by insertion of acetone into the silacyclopropene. Liberation of dimethylsilyl-ene species from either direct photolysis of 56 or decomposition of the silacyclopropene results in the formation of PhC=CSiMe3. Product 59... 

However, the most interesting products could be obtained upon the radiolysis of butadiene derivatives included in a host matrix ( - ) For a number of monomers with a non-centrosymmetric molecular structure it could be demonstrated that y-irradiation leads to stereoregular, optically active polymers in a direct asymmetric induction. Especially these studies indicate that apart from polymerization in solution using optically active catalyst systems (A), the solid state polymerization represents a suitable method to obtain stereoregular polybutadienes. 

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