Ethylene derivatives 1.3- dienes, synthesis

Anthracene homologs can also be prepared in this way, by using derivatives of cyclohexadiene. Further, 1,4-naphthoquinone can be used as starting material (for a single diene synthesis) and the ethylene bridge may be substituted without destroying the ability of the product to split off the ethylene derivative. 

A short synthesis of ( )-isostegane, a tetracyclic dibenzocycloota-diene lactone, has been achieved by a sequential double a, -substitution of an electron-deficient ethylene derivative, in this case zl P-butenolide, followed by non-phenolic oxidative coupling with VOFg . An equally short synthesis of methyl jasmonate has been achieved through 1,4-addition-alkylation of cyclopentenone . 

Synthesis of ethylene derivatives from 1,3-dienes with migration of a carbon-carbon double bond... 

A cyclobutene ROCM sequence was also used in a synthesis of racemic sporochnol (410), a naturally occurring feeding deterrent toward herbivorous fish (Scheme 80) [170]. Exposing cyclobutene 406 (0.01 M in boiling 1,2-dichloroethane) in the presence of ethylene to second-generation catalyst C (8 mol%) led to 1,5-diene 407 in 73% yield, along with 9% of the homodimer derived from 407 by involving the less hindered double bond. Site-selective hy-... 

Drawn from these examples it is apparent that controlling the chemose-lectivity in inter-intermolecular Heck-Diels-Alder reactions of two different alkenes can be tedious if the alkenes show comparable reactivities. Nevertheless, the stepwise approach was realized in several other cases. In a synthesis of a derivative of cephalostatin 1 containing a central benzene instead of the pyrazine ring, Winterfeldt et al. linked two steroidal systems by a Heck coupling and subsequently performed high pressure Diels-Alder reactions of the conjugated diene with electron-deficient alkynes [34], Another example, reported by Hayashi et al., involves a selective Heck reaction of a bromoglu-cal with ethylene or acrylic acid derivatives followed by cycloadditions with maleic anhydride or N-phenylmaleimide [35]. 

We previously described in detail the synthesis and several properties of ethylene-propylene-based terpolyiJKrs containing diene systems as random pending groups. For the sake of completeness we outline here some general conclusions derived from the previous work. 

A comonomer for the synthesis of ethylene/propene elastomers - 2-ethylidene-norbomene (7) - is synthesised via a Diels-Alder cycloaddition of cyclopenta-diene and butadiene followed by an isomerization with titanium-based catalysts of the intermediate 2-vinyl derivative 6 in excellent yield (98 %) (eq. (12)) [22]. 

This reaction is applied to a wide range of alkenes such as acrylic esters, styrene, ethylene, 1-alkene, 1,3-dienes, allyl chloride, allyl acetate, and vinyl ethers [122]. Tolerance of the arylmercury compounds to polar functional groups in the substrate renders the reaction applicable to the synthesis of many functionalized styrene derivatives. A ferrocenyl mercury compound undergoes addition to alkene via the Heck type reaction of methyl methacrylate (Eq. 5.29) [123]. 

The results of the investigated cross-metathesis reactions of silicon containing norbomene derivatives with ethylene showed a poor reactivity for some substituents. Reactive chlorosilanes act as catalyst poisons and silazanes diminish the catalyst s activity by coordination of nitrogen to the metal center. Starting from norbomene derivatives with alkoxy-substituted silicon moieties, a selective synthesis of new silicon-containing a,(0-dienes could be accomplished (Scheme 2). 

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