Dienes rearrangements with

Diallylsulfonium salts undergo intramolecular allylic rearrangement with strong bases to yield 1,5-dienes after reductive desulfurization. The straight-chain 1,5-dienes may be obtained by double sulfur extrusion with concomitant allylic rearrangements from diallyl disulfides. The first step is achieved with phosphines or phosphites, the second with benzyne. This procedure is especially suitable for the synthesis of acid sensitive olefins and has been used in oligoisoprene synthesis (G.M. Blackburn, 1969). 

Carboxylic acids react with butadiene as alkali metal carboxylates. A mixture of isomeric 1- and 3-acetoxyoctadienes (39 and 40) is formed by the reaction of acetic acid[13]. The reaction is very slow in acetic acid alone. It is accelerated by forming acetate by the addition of a base[40]. Addition of an equal amount of triethylamine achieved complete conversion at 80 C after 2 h. AcONa or AcOK also can be used as a base. Trimethylolpropane phosphite (TMPP) completely eliminates the formation of 1,3,7-octatriene, and the acetoxyocta-dienes 39 and 40 are obtained in 81% and 9% yields by using N.N.N M -tetramethyl-l,3-diaminobutane at 50 in a 2 h reaction. These two isomers undergo Pd-catalyzed allylic rearrangement with each other. 

Irradiation of a benzene solution of 7-benzyl-2,5-diphenyl-3,4,7-triazanorcara-2,4-diene (15) with a high-pressure mercury lamp (Pyrex filter) results in a photochemical walk rearrangement to give 4-benzyl-3,7-diphenyl-477-l, 2,4-triazepine (16) in 53 % yield, accompanied by A-benzyl-3,6-diphenylpyridazin-4-amine (6%), 1-benzyl-2,3-diphenylpyrrole (1%) and... 

Electronically rich 1,3-butadienes such as Danishefsky s diene react with chromium alkenylcarbene complexes affording seven-membered rings in a formal [4S+3C] cycloaddition process [73a, 95a]. It is important to remark on the role played by the metal in this reaction as the analogous tungsten carbene complexes lead to [4S+2C] cycloadducts (see Sect. 2.9.1.1). Formation of the seven-membered ring is explained by an initial cyclopropanation of the most electron-rich double bond of the diene followed by a Cope rearrangement of the formed divinylcyclopropane (Scheme 65). Amino-substituted 1,3-butadienes also react with chromium alkenylcarbene complexes to produce the corre-... 

An interesting phenomenon has been observed in the high pressure Diels-Alder reactions of the l-oxa[4.4.4]propella-5,7-diene (117) with 1,4-naphthoquinone, maleic anhydride and N-phenylmaleimide, where the diene 117 undergoes a rearrangement to the diene isomer 118 which, although thermodynamically less favored, exhibits a greater reactivity [40]. The reactivities of the three dienophiles differed since maleic anhydride and N-phenylmaleimide reacted only in the presence of diisopropylethylamine (DIEA) and camphorsulfonic acid (CSA), respectively (Scheme 5.15). The distribution of the adduct pairs shows that the oxygen atom does not exert a consistent oriental dominance on TT-facial selectivity. 

The similarity of the MS spectra of isoterpinolene (11), terpinolene (12), a-terpinene (13) and the alio-ocimene (7) is striking. Whereas the hydrogen rearrangements suggested to explain this similarity might be speculative, they offer a reasonable explanation for the almost identical MS of the open and closed diene structures with that of the triene (7) spectrum. 

Diepoxidation of a diene Diepoxidation of the diene 1 with m-chloroper-benzoic acid gives a mixture of the d,l- and meso-diepoxides, whereas Sharpless epoxidation results in d- or 1-2 by a double asymmetric epoxidation. On treatment with base, 2 rearranges to the diepoxide a and then cyclizes to the meso-tetra-hydrofuran 3, a unit of teurilene, a cytotoxic C, -cyclic ether of red algae. This... 

The product 303 from disulfur dichloride and 2,3-dimethylbuta-l,3-diene rearranges spontaneously to the tetrahydrothiophene 304 (equation 159)150. The reaction of liquid sulfur dioxide with conjugated dienes 305 (e.g. butadiene, isoprene) results in cyclic sulfones which dissociate into their components on heating (equation 160)151 152. 

It should be noted that the stereochemical aspects of the Cope rearrangement are widely used for synthesis of various natural products, e.g. of the elemene-type derivatives 493-496 starting from germacrene-type sesquiterpenes 492 having cyclodeca-1,5-diene structure with stable conformations (equation 186)244. 

The preparation of conjugated diene complexes will be presented by groups. In addition, isomerization reactions, or degenerate rearrangements with activation energies >25 kcalmol-1, will be considered in this section. 

The complete shift of a conjugated diene to a new conjugated diene system has also been observed in the -ionone system (33). Such diene rearrangements require a stoichiometric quantity of Fe(C0)5. The rearranged diene ligand is conveniently liberated from the Fe by oxidation of the complex with FeCls-... 

Reactions of pcrfluoroalkadienes with antimony(V) fluoride are similar to those of per-fluoroalkenes. Terminal dienes 1 rearrange with antimony(V) fluoride at 0-20 C selectively to internal dienes 2, in which the terminal trifluoromethyl groups are predominantly in the configuration.3,37,38 Higher temperatures and a threefold excess of catalyst lead to cyclo-pentenes (see Section 5.3.3.1.). 

The alkoxymercuration of conjugated dienes is more complex since these compounds are less reactive than simple alkenes and the products often react further to afford dimercurated products whose regio- or stereo-chemistry is strongly affected by the initial product. For example, 1,3-butadiene, 1,3-pentadiene, 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene react with meicuiy(II) acetate in methanol to produce 1,2-adducts (equation 265).443-446 These adducts sometimes rearrange with time.446 1,3-Butadiene reacts further to afford primarily the meso adduct of double 1,2-additions.447 Surprisingly, little additional work has been reported on reactions of conjugated dienes. 

Photochemically, a [1,3] suprafacial shift of hydrogen is allowed, and has been observed with several 1,3-dienes rearranging to the unconjugated 1,4-... 

Cope rearrangement (10, 31). The Pd(II)-catalyzed Cope rearrangement of chiral 1,5-dienes occurs with virtually complete 1,4-transfer of chirality.1 Example ... 

A number of reactions are known, however, in which more extensive rearrangements of bonds occur and which involve cyclic intermediates or products. The Diels-Alder reaction is a classical example of this. In the normal Diels-Alder reaction a Ci s-1,3-diene reacts with an ethylene derivative (dienophile) to form a cyclohexene ... 

In entry 28 is an example of Fe-H addition to conjugated dienes, while the Si-Fe bond remains intact. With isoprene, the initial product from 1,4-addition is a cr-allyl compound, which then rearranges with loss of CO to a 77--allyl derivative. This opens a useful route to other functionally substituted derivatives. 

Conjugated dienes, i.e. 1,3-butadiene and 2,3-dimethyl-1,3-butadiene, added fluorine at 0°C ionically, without rearrangement, with formation of 1,2- and mainly 1,4-difluoro adducts in contrast, xenon difluoride afforded exclusively 1,2-adducts. 1,3-Pentadienes, both cis and trans, gave mostly rearranged products [49] ... 

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