Hydrogen chloride conjugated dienes

This procedure illustrates a recently published, simple, general method for the synthesis of conjugated dienes from olefins. The scope of the reaction is shown in Table I.5 In most of these examples hydrogen bromide. .elimination can be effected by stirring a solution of the olefin-bromo-methanesulfonyl bromide adduct in methylene chloride with one equivalent of triethylamine at room temperature. Only two equivalents of the more costly potassium tert-butoxide are then needed in the second elimination step the yields using the two-base procedure are generally superior to that obtained using only potassium tert-butoxide. 

Conjugated dienes can be reduced to monoolefins by treatment with hydrogen, hydrated cobalt chloride, potassium cyanide, potassium chloride, sodium hydroxide, and tetramethylammonium chloride or benzyltri-ethylammonium chloride as the phase-transfer catalyst. The hydridopen-tacyanocobaltate anion, HCo(CN)s3, is the probable metal catalyst (47-... 

Chloro-l,3-dienes are stereoselectively formed via c/.v-halocarborative addition of al-kenes to alkynes in the presence of catalytic amounts of palladium(II) chloride, lithium chloride and oxygen46. The reaction proceeds via cis chloropalladation of the alkyne and c/.v-orientated alkene insertion, followed by /(-hydrogen elimination. Alternatively, 1.4-dienes are obtained if, for steric reasons, a. nn-periplanar /(-hydrogen atom is not available to form the conjugated diene (e.g., after m-orientated insertion of cyclohexene)46. 

Electrophilic addition is the characteristic reaction of alkenes, and conjugated dienes undergo addition with the same electrophiles that react with alkenes, and by similar mechanisms. Hydrogen chloride, for example, adds to the diene unit of 1,3-cyclopentadiene to give 3-chlorocyclopentene. Mechanism 10.3 is analogous to the electrophilic addition of HCl to alkenes. 

The conjugated diene moieties in 3 and 5 were not reduced (Scheme Many heteroatom functional groups can be tolerated in this reduction. Thus, for example, allylic chlorides, such as 7, are not competitively reduced. i Even the comparatively labile imine and N—O bonds in 9 were not hydrogenated (Scheme... 

The conversion of non-conjugated dienes and partially-conjugated trienes to cyclic peroxides has been investigated. In an extension of previously published work, Bloodworth and Khan have obtained high yields of cyclic peroxides by reaction of dienes with hydrogen peroxide in the presence of mercuric nitrate, followed by treatment with chloride ion. This cycloperoxymercuration procedure, as it is known, gave much higher yields of peroxides over those obtained by conventional acid-catalysed oxidation of diols. 

Catalytic hydrogenation of both double bonds yielded the quinolizidine-1,4-dione ( )-2234, the ketone of which was converted into a vinyl triflate before Stille coupling with aUyltributylstannane afforded the conjugated diene ( )-2235. Hydrogenation then produced a 5 2 mixture of racemic di-astereomers 2236 and 2237, which were separated by HPLC. Finally, addition of allylmagnesium chloride to the separated lactams followed by reduction of the adducts with sodium cyanoborohydride gave ( )-quinolizidine 2071 (rac-1728) and ( )-l-ept-quinoHzidine 2071 (rac-2238) as the sole isomers from 2236 and 2237, respectively. 

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