Polyenes synthesis

Polychloromethylsulphonylbiphenyls, mass spectra of 154, 155 Polyenes, synthesis of 771 Polymerization, of sulphoxides 846 Polymer-supported reagents 928 Polymorphonuclear leukocytes 854 Poly(olefin sulphonejs, radiolysis of 916-922 Polysulphones, radiolysis of 913 Population analysis 14, 15, 21, 22 Propargylic sulphenates, rearrangement of 736-739... 

Nucleophilic additions to carbonyl groups lead to alcohols which on dehydration, furnish alkenes70,71. This two-step protocol has been extremely useful for diene and polyene synthesis with wide variation in the carbonyl substrate and the nucleophilic addendum. Diene synthesis using aldol-type condensation as well as phenyl sulphonyl carbanion (the Julia reaction) are also discussed in this section. 

TABLE 14. Polyene synthesis through the Wittig reaction... 

Polyene synthesis. The Vedejs trienic phosphorane 1 (6,14-15) is useful for synthesis of bifunctional all-tram polyenes, since the mixture of (E)- and (Z)-... 

Alkene bonds more remote from the carboxyl function do not interfere wiA the normal Kolbe coupling reaction. An example of this point during a polyene synthesis is given by the formation of the insect pheromone 19 [100]. 

Normant, J.-F. Alkyne Carbocupration and Polyene Synthesis. In Organocopper Reagents A Practical Approach, Taylor, R. J. K., Ed. Oxford University Press Oxford, 1994 pp 237-256. 

The McMurry reaction involving low-valent titanium species accomplishes coupling of two carbonyl groups to furnish aUcenes. The low-valent titanium species is generated either from TiCls/LAH , TiCls/Mg or TiCU/Zn-Cu. When one or both carbonyl substrates carry one or more additional double bonds, dienes or polyenes result from this reaction (equation 109) . The McMurry coupling reaction is remarkably selective and a wide variety of functionalities are tolerated. This reaction can be carried out in both inter- and intramolecular modes to furnish a variety of dienes and polyenes. Synthesis of dienes and polyenes where McMurry coupling has been a key reaction is given in Table 21 . 

The allyl phosphine oxide approach to diene and polyene synthesis has been used by Lythgoe28- in his vitamin D3 synthesis, and by Pattenden29-1 in syntheses of compounds such as 31. 

High-yielding Suzuki substitutions of halogen in halo-boronates are also possible using Al-methylimino-diacetic acid (MIDA) to form the protected boronate, which resists coupling under anhydrous conditions. This approach has been applied to aryl and heteroaryl (only thiophene and benzofuran, shown below) systems, and also for polyene synthesis. ... 

Polyene synthesis. In the presence of titanocene bis(triethyl phosphite), activated alkynes react with (Z)-alkenyl sulfones to give conjugated dienes in a highly legioselective and stereoselective fashion. Mixed unsaturated sulfones react in an analogous manner, and when the titanated coupling adducts are quenched with carbonyl compounds it results in 1,2,4-trienes. ... 

Polyene synthesis. Allylidenetriphenylphosphorane (1) reacts with methyl cw-3-chloropropenoate (2) to form the stabilized yhde (3), presumably by Michael addition (a) and loss of chloride ion (b), and deprotonation. The ylide reacts with aldehydes and ketones to form polyenes, (4) and (5). 

The application of metathesis catalysis to polyene synthesis may be viewed as following a progressive path from polymerizing acetylene itself, a two-membered ring , to ring-opening a... 

Carotenoids, Retenoids, Pheromones and Polyenes.-A convenient route to exclusively ( )-allylic phosphonates (e.g. 165), compounds which are useful in polyene synthesis, is provided by the base-catalysed isomerisation of the corresponding vinylphosphonates. " The bis(trifluoromethyl) analogue (167) of a known, potent squalene synthase inhibitor has been synthesised using the Wittig reaction of (166) with hexafluoroacetone as a key step. ... 

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