WHITING Diene synthesis

WHARTON Olefin synthesis 412 WHITING Diene synthesis 413 WIDEQUIST Cyclopropane synthesis 414 Widman 318 Wiechell 134 Wieland 20... 

WHITING Diene synthesis Diene synthesis trom 2-alkyne-1,4-diols with LAH. 

When a carbonyl moiety is the ene component of a 1,6- or 1,7-diene system, the ene reaction is more favorable. Heating 698 to 110°C, for example, led to a 94% yield of 699 in White s synthesis of 2-desoxystem-odinone.5 5 In 845, the Jt-bond of the aldehyde carbonyl and the Jt bond of the cyclohexene unit constitutes a 1,6-diene, which is more easily seen in the conformational drawing. The reaction occurred at a very reasonable temperature, in good yield, and with excellent stereoselectivity due to the rigid nature of the tricyclic system. 

A useful synthesis of benzo[c]furans, based on experiments described by Ried, has been published by White et It consists of the Diels-Alder reaction of an acyclic diene with dibenzoylacetylene (146) and subsequent ring closure of the resulting 1,2-diaroylcyclohexadiene with /j-toluenesulfonic acid in benzene there has, however, been one report where this... 

White peach scale. Several scale sex pheromones have now been elucidated each of them possesses an asymmetric center and usually a trisubstituted alkene link within an isoprenoid framework (43). The structure of the white peach scale pheromone, R,Zb-II (Figure 8), lent itself to synthesis with another chiral starting material, namely limonene (44). Selective ozonlysis followed by workup with dimethyl sulfide-methanol provided a ketoacetal, III. Wittig methylenation followed by hydrolytic cleavage of the acetal gave a dienaldehyde, IV. Conversion of the aldehyde via the acid to an amide (45) with enantiomerically pure ot-methylbenzylamine permitted chromatographic assessment of the purity of the diene aldehyde (and the limonene). The required R-isomer of the diene aldehyde was >48% ee. 

Bruce, D. A., A. P. Wilkinson, M. G. White, J. A. Bertrand, The synthesis and characterization of an Aluminophosphate with chiral layers, rrans-Co(dien)2 AI3P4O16 3H2O , J. of Solid State Chemistry, 125,228-233 (1996). 

Natural rubber, a terpene composed of repeating isoprene units, is isolated from latex, a sticky white fluid that oozes from Hevea brasiliensis, the South American rubber tree, when its bark is cut. The word rubber was first suggested by English chemist Joseph Priestly in 1770, when he used latex to rub out pencil markings. Rubber is a polymer containing 1,5-diene units in which all the double bonds have the Z configuration. In Chapter 30, we learn about the synthesis and properties of polymers like rubber. 

A general synthetic route to several polyhydroxylated agarofurans was developed by J.D. White and co-workers and the total synthesis of (+)-euonyminol was achieved. The key intermediate was prepared via a Diels-Alder reaction between a diene and a substituted benzoquinone. The resulting bicyclic homoannular diene was reduced under the Luche conditions with excellent regio- and stereoselectivity at C6. The substrate was mainly in the boat conformation and the (3-face of the ketone was more exposed to hydride attack. The C6 ketone was also more sterically accessible and more basic than the C9 ketone functionality. 

D.A. Bruce, A.P. Wilkinson, M.G. White, and J.A. Bertrand, The Synthesis and Characterization of an Aluminophosphate with Chiral Layers trans-Co(dien)2 A13P4016 3H20. J. Solid State Chem., 1996, 125, 228-233. 

The reaction of a diene with a three-carbon, two-electron species in a [4+3] cycloaddition (Figure 2) has been studied extensively for the synthesis of seven-membered rings. Noyori, ° Hoffmann, White,Mann, Harmata, " Trost, Giguere, and others have reported spectacular examples of these processes, a few of which are illustrated here. ... 

Triptans have provided a futile ground for indole synthesis employing both the Heck and the intramolecular Heck reaction. In Glaxo s process synthesis of naratriptan, the reaction of 5-bromoindole with A -methyl-4-piperidone gave the A -methyl-tetrahydropyridinyl substituted indole. The Heck reaction between the 5-bromoindole and the A -methylvinylsulfonamide was carried out on 700-g scales. Both double bonds of the resulting diene were hydrogenated to give naratriptan hydrochloride as white crystals in 71% yield after recrystallization from hot water. 

Helquist and his co-workers have now given more useful experimental details of the stereoselective synthesis of trisubstituted olefins by addition of alkyl-copper complexes, especially methylcopper, to acetylenes (Scheme 8). Clean results are obtained consistently only if the copper(i) bromide-dimethylsulphide complex (22) is white in appearance and its solutions are colourless. If either the solid or solution develops a pink colour (indicative of Cu" salts) then larger amounts of dienes formed from coupling of the alkenyl-copper intermediates (23), are obtained. Complex (22) is best stored under nitrogen, although manipu-... 

Occidentalol is a eudesmane-type sesquiterpene isolated from the wood of Eastern white cedar Thuja occldentalis Linn.), and is characterized by the presence of a c/s-fused decalin system and a homoannular 1,3-diene unit in the molecule, an intriguing combination of functional groups rarely encountered in this class of natural products. Three related syntheses of occidentalol, all of which are based on hexahydronaphthalen-2-one intermediates have been reported, and utilize the carbonyl group for introduction of the diene chromophore in ring A 1-3,5 synthesis outlined below, utilizing a c/s-fused decalone derivative (A) illustrates several of the key features of these syntheses. 

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