Vinyl cyclopentadiene synthesis

Another useful-looking photochemical approach to five-membered-ring carbo-cycle synthesis is by way of di-7r-methane type rearrangement of 3-vinylcyclo-propenes [e.g. (44)- (45)]. This approach to cyclopentadiene synthesis shows features not dissimilar to the method involving base treatment of vinyl gem-dibromocyclopropanes [e.g. (46)- (45)]. ... 

Stable aryl boronates derived from tartaric acid catalyze the reaction of cyclo-pentadiene with vinyl aldehyde with high selectivity. Chiral acyloxy borane (CAB), derived from tartaric acid, has proved to be a very powerful catalyst for the enantioselective Diels-Alder reaction and hetero Diels-Alder reaction. Scheme 5 23 presents an example of a CAB 73 (R = H) catalyzed Diels-Alder reaction of a-bromo-a,/i-cnal 74 with cyclopentadiene. The reaction product is another important intermediate for prostaglandin synthesis. In the presence of... 

Saturated 2-vinyl-5(47Z)-oxazolones have been widely used as intermediates for the synthesis of polymeric compounds that will be described in Section 7.3.2.9. Apart from these polymerization reactions, the Diels-Alder reactions of 4-sub-stituted-2-vinyl-5(47/)-oxazolones 134 with cyclopentadiene are reported to give norbomenyl oxazolones 135 that are useful to prepare norbornenyl functionalized resins by azlactone ring-opening addition reactions (Scheme 7.39). 

The synthesis from 5-benzyloxymethyl-l,3-cyclopentadiene and (/ )-p-tolyl vinyl sulfoxide of the ketone (6), a key intermediate in the Corey prostaglandin synthesis, nicely illustrates these methodologies [530],... 

Molecular oxygen inserts into substituted cyclopentadienes under acidic conditions producing pyrylium salts a hydroperoxide rearrangement is proposed <05JOC5768>. In a further development of the use of benzotriazole (Bt) in synthesis, P-lithiation of the vinyl ether 16 and quenching of the anion with chalcone affords an enol ether. Cyclisation with PCI5 produces 2,4,6-triarylpyrylium salts <05S245>. 

Catalytic asymmetric synthesis of the key intermediate 11 in the preparation of 3/1.8/ , 10a-trihydroxycapnellene and 3/ ,8/J,10a,14-telrahydroxycapnellene is achieved upon treatment of 5-methyl-5-(3-trifluoromethanesulfonyloxy-3-butenyl)-1.3-cyclopentadiene (10) with catalytic amounts of palladium(II) acetate, (S)-BINAP and tetrabutylammonium acetate in dimethyl sulfoxide. The (.STS..S (-enantiomer of 11 is obtained in 89% yield and 80% ce23,8 . In a similar cyclization reaction of the substrate which contains a vinyl iodide unit in the side chain, a much lower asymmetric induction w7as observed. 

Synthesis of these adducts was realized in very short times compared with the same reactions under the action of classical heating. The efficiency of the MW process is all the more noteworthy because the three dienophiles (dimethylbutadiene, cyclopentadiene, and ethyl vinyl ether) are volatile. Although an excess of these reagents relative to 3 was used, the adsorption power of graphite was responsible of their retention, because the temperature of the reaction mixture exceeded their boiling points of approximately 120-130 °C. 

A number of cycloaddition reactions involving allene derivatives as dienophiles have been recorded. Allene itself reacts only with electron-deficient dienes but allene carboxylic acid or esters, in which a double bond is activated by conjugation with the carboxylic group, react readily with cyclopentadiene to give 1 1 adducts in excellent yield. For example, the allene 12 gave, with very high yield and selectivity, the cycloadduct 13, used in a synthesis of (-)-P-santalene (3.19). An allene equivalent is vinyl triphenylphosphonium bromide, which is reported to react with a number of dienes to form cyclic phosphonium salts. These can be converted into methylene compounds by the usual Wittig reaction procedure (3.20). 

Bicyclo[2.2.1]heptanes are widely distributed in namre among the bicyclic ter-penes, and the Diels-Alder reaction provides a convenient method for their synthesis. Thus, cyclopentadiene and vinyl acetate react smoothly on warming to form the adduct 49, which is easily transformed into norcamphor 50 and related compounds (3.44). 

Dienophiles such as nitroethene 56, a-chloroacrylonitrile 57, and vinyl sulfoxide 58 can be used as ketene equivalent in the synthesis of organic compounds to improve the yield of the products. The cycloadducts of cyclopentadiene derivatives obtained from these dienophiles are used in the synthesis of prostaglandins. 

In 2004, Fossey and Richards [21] reported the synthesis of 2,6-bis(2-oxazolinyl) phenylplatinum(I I) NCN-Pincer complexes (63a-d) (Scheme 16.20). These cationic complexes were employed as Lewis acid catalysts for the Michael reaction between methyl vinyl ketone (49c) and ethyl cyanoacetate (64) and Diels-Alder reaction between acrylonitrile (67) and cyclopentadiene (14). The highest rates of the Michael reactions were observed when Pt-oxazolines (63a) and (63b) were used as catalysts, and the lowest rates of the Diels-Alder reaction was observed when Pt-oxazoline (63c) was used as a catalyst. Introduction of a nitro substituent on para position as shown for (63c) resulted in higher Lewis acidity but reduced catalytic activity. 

Show the reaction involved, (b) It can also be prepared by allowing cyclopentadiene to react with vinyl chloride and treating the product with a base. Outline this synthesis. 

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