Ethylene derivatives enynes

Alkeiie oxides s. Oxido compounds Alkenes s. Ethylene derivatives Alkenynes s. Enynes Alkoxides s. Alkali alkoxides Alkoxinies... 

Substitution of the ethylenic carbons in a conjugated enyne by either an electropositive group in the 3-position or by an electronegative group in the 4-position favors addition to the acetylenic group. G. F. Bettinetti, G. Desimoni, and P. Griinanger, G. 94, 91 (1964) cyclopropane ring from ethylene derivatives in methanol s. F. Wessely and A. Eitel, M. 95, 1577 (1964). 

Alkenes s. Ethylene derivatives Alkenynes s. Enynes Alkoxides... 

Blechert carried out a tandem reaction of enynes in the presence of olefins instead of ethylene (Scheme 21). Treatment of cyclopentenol derivative 58a with Ic in the presence of an alkene affords 59a. The five-membered ring in estrone 58b is cleaved by Ic to give 59 and an alkene part is introduced on the six-membered C ring. However, cycloalkenyl amine derivative 60 is treated in a similar manner in the presence of an allyl alcohol derivative to give pyrrolidine derivative 61, and in this case, an alkene part is introduced on the diene moiety. Presumably, ruthenium carbene complex XVI reacts with an alkyne part to produce the pyrrolidine ring with a regioselectivity opposite to the other cases. 

Quite recently, the alkenylative cyclization of enynes with ethylene was achieved using Cp RuCl(cod) as a precatalyst at room temperature [92]. This mild and selective transformation was applied to a sulfonamide 95 to produce the corresponding pyrrolidine derivative 96 (Eq. 37). A ruthenacyclopentene intermediate was proposed for this novel cyclization. 

Norbornene derivatives bearing two alkynes undergo cascade enyne metathesis reactions when treated with a first generation ruthenium carbene and ethylene, giving heterocyclic dienes [28]. The ROM of the norbornene moiety initiates the cascade enyne RCM reactions (Scheme 14). When ethylene is replaced by a monosubstituted alkene, a single enyne RCM takes place, after the initial ROM of norbornene. 

It is usually more convenient, as in the Heck reaction, to use a stable and soluble Pd(ll) derivative such as bis(triphenylphosphine)palladium(ll) chloride instead of Pd(0). This is rapidly reduced in situ to give a coordinatively unsaturated, catalytically active, palladium(O) species. The geometry of the alkene is generally preserved so that cis (Z) and trans (E) dichloro-ethylene give the two different geometrical isomers of the enyne below in >99% stereochemical purity as well as excellent yield. 

Treatment of an alkyne/alkene mixture with ruthenium carbene complexes results in the formation of diene derivatives without the evolution of byproducts this process is known as enyne cross-metathesis (Scheme 22). An intramolecular version of this reaction has also been demonstrated, sometimes referred to as enyne RCM. The yield of this reaction is frequently higher when ethylene is added to the reaction mixture. The preferred regiochemistry is opposite for enyne cross-metathesis and enyne RCM. The complex mechanistic pathways of Scheme 22 have been employed to account for the observed products of the enyne RCM reaction. Several experiments have shown that initial reaction is at the alkene and not the alkyne. The regiochemistry of enyne RCM can be attributed to the inability to form highly strained intermediate B from intermediate carbene complex A in the alkene-first mechanism. Enyne metathesis is a thermodynamically favorable process, and thus is not a subject to the equilibrium constraints facing alkene cross-metathesis and RCM. In a simple bond energy analysis, the 7r-bond of an alkyne is... 

Coupling an ROM event with enyne metathesis opens up further possibilities for RRM. As already discussed for reactions involving only olefins, norbomenes are valuable strained cycloolefins for the ring-opening step [22], Treatment of the norbomene derivative 123 with the first-generation Grubbs catalyst 1 under ethylene atmosphere induced a smooth domino ROM/enyne RCM/diene RCM process with quantitative formation of the tricyclic compound 124 (Scheme 2.45) [22b]. 

The synthesis of block copolymers via ROMP of conventional monomers has been the focus in the last 10 years. This has included making block copolymers via sequential polymerization of different ROMP monomers as well as those made from a combination of ROMP with other polymerization techniques [74, 141] A metathesis approach has been reported involving ROMP combined with the polymerization of 1,6-heptadiynes by molybdenum or ruthenium initiators [142,143], or with monomers allowing enyne metathesis polymerization [144]. Choi et al. [145] prepared block copolymers of NBE derivatives with a 6-heptadiyne derivative leading to an in situ crosslinking of the conjugated segment and in turn to nanoparticle formation. Moreover, a combination of ROMP and insertion polymerization of ethylene has also been reported [146]. 

Further work from Vollhardt s group on cobalt-catalysed cycloadditions of olefins and acetylenes has led to a synthesis of cyclohexadiene derivatives (188 n = 0—2) by addition of trimethyl silylacetylenes the reactions can also be carried out in an intramolecular sense, leading to tricyclic compounds. The novel tricyclic compound (189) has been obtained from naphthoquinone by a [2 + 2]addition of l,l-bis(silylmethyl)ethylene followed by treatment with a Lewis acid. A key step in the first total synthesis of a decipiene diterpene is the formation of tricyclic ketone (190) by an intramolecular aldol condensation, which required the use of methanolic barium oxide. ... 

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