Christo Jossifov

Speculations on a possible mechanism of a tungsten catalyzed 1,2,3,3-tetraphenylprop-2-en-1-one polymerization

Abstract A mechanism is suggested for the reaction of 1,2,3,3-tetra-phenylprop-2-en-1-one (1) under the influence of some tungsten compounds containing WO or WC bonds. The processes involved in the polymerization of 1 are described as redistribution of atoms (C, O and W), involving four-membered metallacyclic transition states. The latter can be visualized by the schemes of olefin metathesis, carbonyl-olefin exchange reaction, reductive coupling of carbonyl compounds etc. These conclusions are confirmed by the fact that the processes under investigation can be catalyzed not only by tungsten oxocompounds but also by the stable Casey carbene.

Synthesis and properties of poly(9,10-anthracene diylidene)

Abstract A new conjugated polymer, poly(9,10-anthracene diylidene) has been prepared by self-condensation of anthrone in poly(phosphoric acid). The polymer exhibited high thermal and oxidative stability, thermochromism, semiconductive and paramagnetic properties.

Polymer formation via reductive coupling of a diketone by metathesis catalytic systems

Abstract It is shown that, not only reduced transition metal reagents, but also two-component Friedel–Crafts catalytic systems (WCl6·AlCl3) are effective for olefin metathesis and coupling of carbonyl compound. Benzil gives polymeric products, whose structures have been elucidated by elemental analysis, IR, UV-vis, 1H- and 13C-NMR spectroscopy.

Recent Applications of Alkene Metathesis in Fine Chemical Synthesis

During the last decade or so, the emergence of the metathesis reaction in organic synthesis has revolutionised the strategies used for the construction of complex molecular structures. Olefin metathesis is indeed particularly suited for the construction of small open-chain molecules and macrocycles using crossmetathesis and ring-closing metathesis, respectively. These reactions serve, inter alia, as key steps in the synthesis of various agrochemicals and pharmaceuticals such as macrocyclic peptides, cyclic sulfonamides, novel macrolides, or insect pheromones. The present chapter is aiming at illustrating the great synthetic potential of metathesis reactions. Shortcomings, such as the control of olefin geometry and the unpredictable effect of substituents on the reacting olefins, will also be addressed. Examples to be presented include epothilones, amphidinolides, spirofungin A, and archazolid. Synthetic approaches involving silicon-tethered ring-closing metathesis, relay ring-closing metathesis, sequential reactions, domino as well as tandem metathesis reactions will also be illustrated.

Copolymerization of a conjugated dicarbonyl compound with a strained cycloolefin mediated by a metathesis catalytic system

A very simple one-pot synthesis of a copolymer consisting of conjugated fragments connected by aliphatic segments is presented. The copolymerization of terephthalaldehyde with norbornene proceeds under the influence of the binary system TiCl3+AlCl3. The products are oligomers with monomodal broad molecular weight distribution (dispersity=2.8; Mw=3900). The IR bands are assigned to aromatic, olefinic and aliphatic C-H vibrations. The absorption in the visible range reveals conjugated blocks in the backbone. The products are soluble in benzene, toluene, chloroform, etc.

Synthesis and properties of 1,5- and 1,8-dichloro-substituted poly(9,10-dihydroanthracene-9,10-diylidene)s

Abstract Two new dichloro-substituted poly(9,10-dihydroanthracene-9,10-diylidene)s were prepared by self-condensation of 1,5-dichloroanthrone and 1,8-dichloroanthrone. The bromination and thermal and semiconductive properties were investigated.

Copolymerization of benzoquinone with norbornene

Abstract For the first time, the conjugated dicarbonyl compound benzoquinone has been copolymerized with the strained cyclo-olefin norbornene using catalytic amounts of the Friedel-Crafts metathesis catalytic system WOCl 4 +AlCl 3 . All analyses reveal that the products consist of conjugated blocks originating from benzoquinone connected with spacers originating from norbornene. The products are soluble in benzene, toluene, chlorobenzene, etc. but possess properties of the conjugated polymers. They have been synthesized via a very simple one-pot procedure.

Carbonyl-Olefin Exchange Reaction and Related Chemistry

A new carbon—carbon double bond forming reaction (carbonyl olefin exchange reaction) mediated by transition metal catalytic systems has been discovered. The catalytic systems used (transition metal halides or oxohalides alone or in combination with Lewis acids) are active only in the case when the two reacting groups are in one molecules and are conjugated. In addition these systems accelerate other reactions which run simultaneously with the carbonyl olefin metathesis rendering a detailed investigation of the process very complicated.

A Possible Mechanism of Polymer Formation from α,β-Unsaturated Carbonyl Compounds Under the Influence of Metathesis Catalytic Systems

In 1983 we discovered a new reaction between an olefinic double bond and a carbonyl group which takes place in the presence of WCl6. We used this reaction to transform several α,β-unsaturated carbonyl compounds into substituted polyacetylenes [1]. The new reaction can be described, like the olefin metathesis, as a cleavage of double bonds and generation of new ones. The final result is a redistribution of atoms (C, O), connected with double bonds. We called this new reaction Carbonyl — Olefin Exchange Reaction (COER).