O-Divinylbenzene

It has been suggested that certain 1,5-dienes including o-divinylbenzene (23),156 vinyl acrylate (24, X 11) and vinyl methacrylate (24, X CH )120 may also undergo cyclopolymerization with a monomer addition occurring prior to cyclization and formation of a large ring. However, the structures of these cyclopolymers have not been rigorously established. 

Oberachert, H., Premstaller, A., Huber, C.G. (2004). Characterization of some physical and chromatographic properties of monolithic poly(styrene-o-divinylbenzene). J. Chromatogr. A 1030, 201-208. 

Note Normally inhibited with 8-12 ppm 4-7er7-butylcatechol to prevent polymerization. According to Chevron Phillips Company (March 2002), 99.93% styrene contains the following components (ppm) benzene (<1), toluene (<1), ethylbenzene (50), a-meth ylstyrene (175), m + p-xylene (120), o-xylene (125), isopropylbenzene (100), / -propylbenzene (60), m + p-ethyltoluene (20), vinyltoluene (10), phenylacetylene (50), m + p-divinylbenzene (<10), o-divinylbenzene (<5), aldehydes as benzaldehyde (15), and peroxides as benzoyl-peroxides (5). 

New P-substituted benzo- and naphthofuryl derivatives of o-divinylbenzene were synthesized and irradiated in order to form annulated bicyclo[3.2.1]octadienes. The mechanism of the intramolecular (2+2]-cycloaddition was explained <99H(51)1355>. 

When the bis-dibromocarbene adduct of o-divinylbenzene is treated with methyl lithium a surprising influence of the reaction temperature on the product composition is noted. 

Probably the most rewarding experiments involving stable carbocation salts have been those using the monomers alkyl vinyl ethers (79-81X N-vinylcarbazole (82), p-methoxystyrene (21,67), cyclopentadiene (86), o-divinylbenzene (92), and to a lesser extent indene (34). 

The homopolymerisation of o-divinylbenzene is complicated by the possibility of intramolecular cyclisation occuring as well as direct propagation e.g. 

The photoinduced cleavage of 217-pyrans to a,/ ,y,8-unsaturated ketones, as reported for 2/f-chromene, has already been discussed. The formation of the 2/f-pyran system from such an unsaturated ketone is also known and has been reported for cis-/3-ionone411 and for the substituted o-vinylbenzophenone (395) which on irradiation at low temperature yields the unstable pyran (396).412 On prolonged photolysis, however, this benzophenone is converted in benzene solution into the epoxide (397) and in methanol solution into the methoxyisochroman (398). It seems probable that a common intermediate exists and that this has the structure 399. A close analogy, therefore, exists between this conversion and the photolysis of o-divinylbenzene in which a similar intermediate is postulated.413,414... 

Hirulog-8 has the formula H-(D-Phe)-Pro-Arg-Pro-(Gly)4-Asn-Gly-Asp-Phe-Glu-Glu-Ile-Pro-Glu-Glu-Tyr-Leu-OH. Hirulog-8 was synthesized by conventional solid-phase peptide synthesis employing an Applied Biosystems 430 A Peptide Synthesizer. This peptide was synthesized using BOC-L-Leucine-O-divinylbenzene resin. Additional t-BOC-amino acids (Peninsula Laboratories,... 

Absolute asymmetric [2 + 2] photocycloaddition in a crystalline CT complex was also found. A series of 1 1 CT crystals of bis[1,2,5]thiadiazolotetra cyanoquinodimethane (BTDA) 148 as an electron acceptor was obtained by mixing with neat arylolefins such as styrene, o-, m-, or /7-divinylbenzene as electron donors. X-ray crystallographic analyses of the CT crystals revealed the chiral nature of the red crystals formed between 148 and o-divinylbenzene oDV due to their belonging to space group P2, while the other cases were achiral. 

Scheme 24) [52], The reaction was much more efficient in the solid state than in solution. When o-divinylbenzene was used, an absolute asymmetric induction leading to the chiral cycloadduct (71% and 95% ee at 15°C and -70 °C, respectively) was observed to occur via a single-crystal-to-single-crystal transformation (P2, P2.). 

In many cases, e.g., with o-divinylbenzene or o-diethynylbenzene, monomeric as well as polymeric cyclic adducts can be isolated.439... 

Sodamide (60 mmoles) in liquid ammonia (300 ml) is mixed with methyltriphenylammo-nium bromide (55 mmoles), and the ammonia is evaporated. The residue is boiled in ether (200 ml) under reflux. o-Phthalaldehyde (28 mmoles) in ether (100 ml) is stirred during 15 min into the orange-yellow solution of methylenetriphenylphosphorane, and the mixture is boiled for 2 h. After removal of the triphenylphosphine oxide, concentration of the filtrate to 50 ml, and then removal of further oxide, the filtrate affords o-divinylbenzene, b.p. 75-78°/14 mm, in 75 % yield (2.7 g). 

Co-trimerization of the unreactive disubstituted acetylenes with acetylene proved possible in some cases. For instance, acetylene with 2-butyne produced benzene, o-xylene (72), tetramethylbenzene (67), and styrene (72, 67). Acetylene and divinylacetylene yielded mainly o-divinylbenzene (13, 74). The co-trimerization of acetylene with vinylacetylene yielded styrene (75). This reaction probably also accounts for formation of styrene during cyclotrimerization of acetylene, because small amounts of vinyl-acetylene are usually present or are formed from acetylene under the reaction conditions. 

Aso et al. [294,295] studied the radical polymerization of pure o-divinylbenzene by AIBN in benzene solution at 20 to 90 °C. The products obtained were either totally or at least partially soluble in organic solvents such as aromatic hydrocarbons or chloroform. A conversion of 70% to a totally soluble product could be reached with [Mo] = 0.6 mol/L at 70 °C. The amount of pendant double bonds in the polymers was determined by use of IR spectroscopy and bromination and found to be 30 to 90% of the maximum value calculated for one double bond per monomer unit. The authors suggested that cyclization had occurred in addition to conventional 1,2-polymerization. 

Anionic polymerization of o-divinylbenzene was examined by Aso et al. [294]. The authors used n-BuLi, phenyllithium, and naphthalene/alkali metal in THF, ether, dioxane, and toluene at temperatures between —78 and 20 °C. Generally, it was found that as with radical and cationic initiators, a competition between cyclopolymerization and conventional 1,2-polymerization occurs, with the tendency for cyclization to be lower than with the other mechanisms. The polymerization initiated with the lithium organic compounds resulted in polymers with up to 92% double bonds per monomer unit (THF, 20 °C). Polymerization with lithium, potassium, and sodium naphthalene also showed a rather weak tendency for cyclization. In THF at 0°C and 20 °C the cyclization tendency increased with decreasing ionic radii of the counter cation, while in dioxane the reverse effect was observed, and in ether still another dependence was found (K > Li > Na). Nitadori and Tsuruta [299] used lithium diisopropyl amide in THF at 20 °C to polymerize m- and p-divinylbenzene. The authors obtained soluble products with molecular weight up to 100 000 g/mol (GPC) and showed the polymers to contain pendant double bonds by IR and NMR spectra. It seemed to be important that a rather large excess of free amine (the initiator was formed by reaction of -BuLi with excess diisopropylamine) was present in the polymerization mixture. In later studies [300,301] a closer view was taken on polymerization kinetics and the steric course of the polymerization reaction. 

Irradiation of p,(3 -dithienyl substituted o-divinylbenzenes (146) and (147) commonly led to intermolecular [2 + 2] cycloadducts (148) and (149). The compound (146) also led to an intramolecular cyclised dihydronaphthalene (150), while (147) afforded a polycyclic compound as a side product. Irradiation of (151) gave a polycyclic compound (152) as a... 

Cyclization occurred in the free-radical polymerization and copolymerization of o-divinylbenzene. Indane units were found in the polymer chains 3, 6, 7). 

Appreciable cyclization accompanies the cationic polymerization of o-divinylbenzene (11-53) (5). The relative magnitudes of x and y depend on the catalyst employed. At 0°C, in toluene as solvent, there was 19 % cyclization with boron trifluoride etherate. Under the same conditions as much as 47.8 % cyclization occurred when stannic tetrachloride was used. 

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