Monocyclic olefins

The early Escherunoser-Stork results indicated, that stereoselective cyclizations may be achieved, if monocyclic olefins with 1,5-polyene side chains are used as substrates in acid treatment. This assumption has now been justified by many syntheses of polycyclic systems. A typical example synthesis is given with the last reaction. The cyclization of a trideca-3,7-dien-11-ynyl cyclopentenol leads in 70% yield to a 17-acetyl A-norsteroid with correct stereochemistry at all ring junctions. Ozonolysis of ring A and aldol condensation gave dl-progesterone (M.B. Gravestock, 1978 see p. 279f.). 

While the foregoing concepts have been utilized to rationalize the product distribution obtained on hydrogenation of a number of monocyclic olefins, it should be noted that the effect of pressure on the stereochemistry of hydrogenation of steroidal double bonds has not been critically evaluated. 

By using a transition metal chloride catalyst and an iodine modified cocatalyst, ring-opening polymerization of C5 and C8 monocyclic olefins is controlled to prepare either cis polymers or trans products that are crystallizable. In copolymerization, the cis/trans units in the copolymers are regulated by adjusting the C5/C8 olefin monomer ratio. As the comonomer is increased, the copolymer becomes less crystalline and then completely amorphous at equal amounts of cis/trans units. Polymerization results are reported from WC16 and MoCl5 catalysts. 

Before discussing the polymerization of monocylic olefins, a brief review of the preparation of polymers from bicyclohep-tenes will acknowledge their historical contribution with respect to polymerization catalysts, polymer structure and properties. Their monomer reactivity in polymerization is much faster than the reactivity of the less strained monocyclic olefins. Anderson (1) and Truett (2) polymerized norbornene... 

Intramolecular cycloadditions of alkenyl-substituted nitrile oxides produce bicyclic isoxazolines. When monocyclic olefins are used, tricyclic structures are obtained. This approach was pioneered by both Kozikowski s and Curran s groups. A typical case involves the cycloaddition of nitro compound 191 [mixture of diastereomers derived from pentenose pyranoside 190], which produced a diaster-eomeric mixture of isoxazolines that contain cis-fused rings (i.e., 192) in near quantitative yield (326) (Scheme 6.85). Further elaboration of this mixture led to epoxycyclopentano-isoxazoline 193, which was then converted to the aldol product in the usual manner. The hydrogenation proceeded well only when rhodium on alumina was used as the catalyst, giving the required (3-hydroxyketone 194. This... 

Simple illustrations of monocyclic olefins bearing unsaturated substituents (Eqt. 13 and 14) are 1-vinyloydohexene 4 J- bonyl-ethinylcyclohexfine,108 and l-phenylcyclohex ne.1M< w 4... 

Monocyclic olefins and diolefins rate below the corresponding saturates. 

Polymers of monocyclic olefins (cyclopentene, cyclooctene) produced by ring-opening metathesis are linear elastomers. Their properties are somewhat similar to those of poly eri-1,4-hn i.idiene). Polymers of dicy-clopentadiene produced with the same catalysts are heavily cross-linked resins displaying high toughness and tensile strength as well as excellent impact strength at low temperatures. 

The first species may be compared with the normal (i.e. non-bridgehead) olefin bicyclo[3.3.1]non-2-ene, 22d. The former is less stable than the latter by some 80 kJmol-1 even though the second species has a —CH=CH— linkage and the first has a >C=CH— linkage. (For calibration, one may compare the relative stability of the hardly strained monocyclic olefins our primary archive shows that of the isomeric 3- and 1-methylcyclopentenes, the latter is more stable69 than the former by 11.2 1.0 kJmol-1.)... 

It has been reported (102) that the equatorial bicyclic ketotosylate 360 (R=CH3) is transformed into monocyclic olefin ester 362 (R=CH3) by treatment with sodium ethoxide while the axial isomer 363 yielded the bicyclic olefin 364. Similarly, compound 360 (R=C00CH3) gave 362 (R=C00CH3 ) (103). Thus, reactions with the equatorial tosylates take place via the stereoelectroni-cally controlled fragmentation of intermediate 361 (R=CH3 or COOC2H5). 

As shown in the Section II, A, daphniphylline (1) and daphmacrine (18), whose stereostructures have been unambiguously determined, have the same amine moiety but differ in the oxygen heterocyclic skeleton. Thus, it is quite reasonable to suppose that two different moieties must be constructed from such a common precursor as A which can be derived from squalene via squalene-2,3-oxide, and from a monocyclic olefin (Scheme X). 

Only a very limited amount of research has been published concerning 10-carbon, monocyclic olefins as ligands. In 1955 Cope and co-workers... 

Polymers formed by ROMP of unsubstituted monocyclic olefins such as cyclopentene [29] contain double bonds that may be cis or trans (1). NMR spectra give not only the proportions of cis and trans double bonds but also the proportions of cc, cr, and tt dyads. Low-cw polymers of norbornene and derivatives usually have a random distribution of the two kinds of double bond but in high-cw polymers the trans double bonds frequently occur in pairs, indicating an influence of the double bond one removed... 

Polymers formed by ROMP of prochiral monocyclic olefins and bicyclic olefins possess chiral centres at regular intervals in the chain, giving rise to dyads which may be isotactic (m) or syndiotactic (r). 2 represents an dXX-trans polymer of 4-methylcyclopentene containing both m and r dyads [31], while 3 represents a polymer of norbornene, also containing both types of tactic dyad [32]. 

ULTRASOUND ASSISTED METATHESIS OF MONOCYCLIC OLEFINS WITH TUNGSTEN-BASED CATALYSTS... 

Metathesis polymers obtained from unsubstituted monocyclic olefins, such as cyclopentene or cyclooctene, can contain two types of repeating units. These are units in which the carbon-carbon double bond has the cis or trans configuration.Sequences of cis- and trans-enchained poly(l-octenylene) are shown in Figure 20.1. 

Polymerization of monocyclic olefins has been carried out with the most important representatives of this series, from cyclobutene to cyclododecene and higher homologues [1-3]. Lower cycloolefins such as cyclobutene and cyclopentene proved to be rather reactive in... 

Depending upon the structure of the olefin, either methyl ketones or epoxides can be formed by treatment with molecular oxygen and a catalytic quantity of [PdCl(N02)(MeCN)2] (Scheme 6). With monocyclic olefins other products are formed, resulting mainly from -elimination of intermediate metallacyclic species. ... 

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