Hydrogenation vinyl functions

The composition of the products derived from hydrogenation of vinyl functions is determined by the relative rates of two competing reactions. 

For example, a proline-based chiral ligand was attached to a vinyl-substituted monomer (Fig. 42.15) by reacting vinylbenzoyl chloride with the amine functionality of the ligand [106]. As mentioned previously, the apolar Merrifield resin as a support is not swollen in polar solvents. Hence, in order to match the polarity of the resin with that of the typically used substrates in enantioselective hydrogenation, the functionalized monomer was copolymerized with polar units of methacrylic acid 2-hydroxyethyl ester. 

While most catalysts reduce the least-substituted double bond preferentially, the novel catalyst system CoBr(PPh3)3 BF30Et2 can selectively hydrogenate conjugated dienes to monoenes via 1,2-hydrogen addition to the more substituted double bond (Scheme 92). Unfortunately, hydrogenation of functionalized alkenes, such as methyl vinyl ketone, methyl acrylate and -butyl vinyl ether, does not occur even under forcing conditions. 

Addition of 5-substituted 2-pyrrolidinones to methyl glyoxylate produces useful precursors (190) to exocyclic A-acyliminium ions (equations 132). The preferred iminium ion geometry is most probably ( ) as depicted in (191) for steric reasons. This geometry explains the stereochemical relationship between the ring junction hydrogen atom and the ester function in the products (192) and (193). Best yields are achieved by using the thermal cyclization of intermediate mesylates, and the major products have the ester and vinyl function trans. ... 

Depending on the substituents of l,6-enynes, their cyclization leads to 1.2-dialkylidene derivatives (or a 1.3-diene system). For example, cyclization of the 1,6-enyne 50 affords the 1.3-diene system 51[33-35]. Furthermore, the 1.6-enyne 53, which has a terminal alkene, undergoes cyclization with a shift of vinylic hydrogen to generate the 1,3-diene system 54. The carbapenem skeleton 56 has been synthesized based on the cyclization of the functionalized 1,6-enyne 55[36], Similarly, the cyclization of the 1,7-enyne 57 gives a si -mem-bered ring 58 with the 1,3-diene system. 

Carbon Cha.in Backbone Polymers. These polymers may be represented by (4) and considered derivatives of polyethylene, where n is the degree of polymeriza tion and R is (an alkyl group or) a functional group hydrogen (polyethylene), methyl (polypropylene), carboxyl (poly(acryhc acid)), chlorine (poly(vinyl chloride)), phenyl (polystyrene) hydroxyl (poly(vinyl alcohol)), ester (poly(vinyl acetate)), nitrile (polyacrylonitrile), vinyl (polybutadiene), etc. The functional groups and the molecular weight of the polymers, control thek properties which vary in hydrophobicity, solubiUty characteristics, glass-transition temperature, and crystallinity. 

Osmium carbonyl (Os3(CO)i2) acts as a photoinitiator of vinyl polymerization [20], which can function without a halide additive. The mechanism of photoinitiation is by a hydrogen abstraction from monomer to pho-... 

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