Subject cyclic olefins

Evidence for this mechanism includes (1) an experiment showing a 4.5% nOe between and of the triene in Eq. (14), validating the -stereochemistry of the exo-cyclic olefin and (2) preparation of a hexadeuterated allenyne that was subjected to the reaction conditions which gave complete transfer of a deuterium atom to the exocyclic double bond of the triene (Eq. 15). 

The Heck reaction is a synthetically powerful reaction wherein a carbon-carbon bond is formed between two sp hybridized carbon atoms. The syn nature of the addition of vinyl-aryl palladium species to carbon-carbon double bond precludes a syn p-hydride elimination for cyclic olefins. As a result, a new chiral center is formed. Shibasaki and Vogl provided a comprehensive review of this subject in 1999 440 Overman and Donde reviewed the intramolecular version of this reaction in 2000. Pfaltz and co-authors specifically reviewed this reaction using PhosOx ligands. ... 

The chiral Mo-alkylidene complex derived from AROM of a cyclic olefin may also participate in an intermolecular cross metathesis reaction. As depicted in Scheme 16, treatment of meso-72a with a solution of 5 mol % 4a and 2 equivalents of styrene leads to the formation of optically pure 73 in 57% isolated yield and >98% trans olefin selectivity [26]. The Mo-catalyzed AROM/CM reaction can be carried out in the presence of vinylsilanes the derived optically pure 74 (Scheme 16) may subsequently be subjected to Pd-catalyzed cross-coupling reactions, allowing access to a wider range of optically pure cyclopentanes. 

Independent interpretation of mass spectroscopic data by Wolovsky 66> and Ben-Efraim, Batich, and Wasserman 6 ) indicate that cyclic olefins subjected to disproportionation conditions form interlocking rings (catenanes) as well as cyclopolyolefins. The proposed scheme involves four-center transition state and Mobius-Strip approach... 

Subjects specifically excluded are cycloolefin polymerizations catalyzed by naked nickel catalysts, palladium-catalyzed ethylene/carbon monoxide alternating copolymerizations, metathesis polymerizations of cyclic olefins, and diene polymerizations... 

Cyclopentadiene [542-92-7] (CPD), CsHe, (1), and its more stable dimer, dicy-clopentadiene [77-73-6] (DCPD), C10H12, (2), are the major constituents of hydrocarbon resins, cyclic olefin polymers, and a host of specialty chemicals. They can be transformed into many chemical intermediates used in the production of pharmaceuticals, pesticides, perfumes, flame retardants, and antioxidants. Because of their wide industrial uses, their chemistry has been extensively investigated and documented. Numerous reviews (1-12) have been published on the subject. The production processes and industrial uses of CPD and DCPD are summarized in Reference 13. In addition to the classical organic reactions, CPD forms organic metallic complexes, ferrocene, with transition metals (14). Some of these complexes have been established as excellent olefin polymerization catalysts. Several reviews have been published on this rapid growing field (15-19) (see Single-Site Catalysts). 

When cyclic olefins are subjected to olefin metathesis, breaking of the double bonds proceeds with opening of the unsaturated cyclic unit, and poly(alkenylenes), that is, macromolecular products that are also known as polyalkenamers, can be obtained (Scheme 20.3). Common examples of cyclic... 

Aldol addition and related reactions of enolates and enolate equivalents are the subject of the first part of Chapter 2. These reactions provide powerful methods for controlling the stereochemistry in reactions that form hydroxyl- and methyl-substituted structures, such as those found in many antibiotics. We will see how the choice of the nucleophile, the other reagents (such as Lewis acids), and adjustment of reaction conditions can be used to control stereochemistry. We discuss the role of open, cyclic, and chelated transition structures in determining stereochemistry, and will also see how chiral auxiliaries and chiral catalysts can control the enantiose-lectivity of these reactions. Intramolecular aldol reactions, including the Robinson annulation are discussed. Other reactions included in Chapter 2 include Mannich, carbon acylation, and olefination reactions. The reactivity of other carbon nucleophiles including phosphonium ylides, phosphonate carbanions, sulfone anions, sulfonium ylides, and sulfoxonium ylides are also considered. 

In the polymer field, reactions of this type are subject to several limitations related to the structure and symmetry of the resultant polymers. In effect, the stereospecific polymerization of propylene is in itself an enantioface-diflferen-tiating reaction, but the polymer lacks chirality. As already seen in Sect. V-A there are few intrinsically chiral stractures (254) and even fewer that can be obtained from achiral monomers. With two exceptions, which will be dealt with at the end of this section, optically active polymers have been obtained only from 1- or 1,4-substituted butadienes, fiom unsaturated cyclic monomers, fiom substituted benzalacetone, or by copolymerization of mono- and disubstituted olefins. The corresponding polymer stmctures are shown as formulas 32 and 33, 53, 77-79 and 82-89. These processes are called asymmetric polymerizations (254, 257) the name enantiogenic polymerization has been recently proposed (301). 

Early work on strained double bonds has been reviewed.7-9 Double bonds in strained bicylic systems and medium-sized cycloalkenes are particularly reactive and add azides quantitatively in an exothermic reaction43-45 81,82 that could be useful in derivatization83 and quantitative analysis.84 The reaction of organic azides with strained, olefinic bonds in cyclic systems, first recorded by Alder,43-45 has been the subject of numerous theoretical and... 

Fig (14) Olefin (107) has been converted to cyclic ether (114) by standard reactions. Its transformation to enone (115) is accomplished by annelation with methyl vinyl ketone and heating the resulting diketone with sodium hydride in dimethoxyethane. The ketoester (116) is subjected to Grignard reaction with methyllithium, aromatization and methylation to obtain the cyclic ether (117). Its transformation to phenolic ester (119) has been achieved by reduction, oxidation and esterification and deoxygenation. 

Cyclic nitro olefins. Some years ago Bachman and Whitehouse reported the Markownikoff addition of mercury(II) nitrite to olefins. The salt is generated in situ from mercury(II) chloride and sodium nitrite. Because of the requirement for an aqueous medium the rate is slow the reaction is also subject to steric effects. 

In marked contradistinction to the above, Vogel, et al. found that when N-methyl- or A -ethyl-2,5-diformyl pyrrole (2.368 or 2.369) are subjected to McMurry conditions, the cyclic trimers 2.370 and 2.371 could be isolated, albeit in yields of less than 1%. Here, H NMR spectroscopic experiments led to the conclusion that these systems were olefinic, rather than aromatic, in nature. These same experiments revealed, however, that 2.370 and 2.371 possess a predominant conformation in which one of the pyrrole rings is rotated outward (as shown in Scheme 2.3.23), presumably, to accommodate the steric bulk of the nitrogen protecting groups. In any event, because of these conformational effects, systems 2.370 and 2.371 have... 

In the laboratory of K. Mori the task of determining the absolute configuration of the phytocassane group of phytoalexins was undertaken. To this end, the naturally occurring (-)-phytocassane D was synthesized from (R)-Wieland-Miescher ketone. During the synthesis, a tricyclic ketone intermediate was subjected to the Shapiro olefination reaction to give the desired cyclic alkene in good yield. 

C.i.a. Sequential Hydroarylation (Hydroalkenylation)/Cyclization. Since the cis stereochemistry of addition pushes the substituents of the acetylenic moiety to the same side of the olefinic double bond, a cyclization reaction can follow the addition step when these substituents bear suitable nucleophilic and electrophilic centers, and the whole process resembles a valuable straightforward methodology for the preparation of cyclic compounds (Scheme 20). Cyclization can occur under hydroarylation(hydroalkenylation) conditions—either before or after the substitution of the carbon-hydrogen bond for the carbon-palladium bond—or by subjecting the isolated hydroarylation(hydroalkenylation) product to suitable reaction conditions. This strategy has been employed successfully to develop new routes to various heterocycles. 

The method is rapid and fairly simple, but subject to variation in the quality of the silica gel employed. The lightest components in gasoline need to be removed from each sample in order to obtain the best results, and certain compound types can elute with the wrong group, for example, cyclic di-olefins elute with the aromatics. The method gives results in... 

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