Rearrangement 1,5-dienes

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. 

Hydrocyanation of aliphatic conjugated dienes in the presence of Ni(0) complexes gives diene rearrangement products and /i.y-unsaUiratcd nitriles in 10-90% yields10. Dienes other than 1,3-butadiene do not produce terminal nitriles, implying that the more highly substituted jr-allyl nickel complex is favored. Thus, reaction of 1-phenylbuta-l,3-diene (1) affords ( )-2-methyl-4-phenylbut-3-enenitrile (2) as the sole product (equation 5). The... 

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-... 

Whereas the hexa-1,3,5-triene/cyclohexa-l,3-diene rearrangement serves as a model reaction in the hydrocarbon series, the perfluoro analog behaves differently, as presented in Section 5.3.2.1. Photolysis of perfluorohexa-l,3,5-triene (8) in the gas phase yields per-fluorobicyclo[2.2.0]hex-2-ene (10) as the major product, presumably via perfluorocyclohexa-1,3-diene (9).4 Perfluoro(3-vinylcyclobutene) is formed as the minor product. Thermolysis of hexa-tricnc 8 gives cyclohexadiene 9.4 Photolysis of 9 provides bicyclohexene 10, which reverts to 9 thermally.5... 

Numerous examples of vinylcyclopropane to diene rearrangement have been studied (e.g. equation 134)178 and thoroughly reviewed in the aforementioned surveys and in this series , and hence will not be repeated here. The reader will also find in this series180 ample examples of typical ring-opening reactions of cyclic vinylcyclopropanes (equation 135)181... 

Cycloaddition of cncdiynes. Photolysis of the enediyne 1 in the presence of catalytic quantities of CpCo(CO)2 in refluxing toluene results in the tricyclic diene 2. The reaction involves a diene rearrangement in the expected product (a).1... 

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-... 

Another type of reactive electron-deficient diene which combines with neutral imines is disulfone (46) (equation 17). Interestingly, this diene rearranges under the reaction conditions to isomer (47) which undergoes regioselective [4 + 2] cycloadditions with neutral imines to give initial adducts such as (48). However, this product suffers a subsequent 1,3-hydrogen shift to provide isolable adduct (49). Independent synthesis and cycloaddition of (47) provided good evidence for the overall reaction padiway shown. 

In acyclic systems, Claisen rearrangements show a well-established prefoence for chair-like transition states. With crotyl propenyl ether, the chair selectivity amounts to 97-98% at 142 C, which corresponds to an approx. 3 kcal mol difference between the fiee energy of activation (AAG ) of chair and boat TS (equation 26). The preference for a chair-like geometry in the TS is even more pronounced in the Cope reaiT ement 99.7% of the 3,4-dimethylhexa-1,5-diene rearranges at 225 C via a chair-like TS, corresponding to a AAG chair-boat of -5.7 kcal mol" . - The latter result closely parallels the difference in energy of the chair and boat conformations of cyclohexane (5-6 kcal mol" ). ... 

Similarly, 2,3-benzobicyclo[3.2.1]octa-2,6-dienes rearrange to 3,4-benzotricyclo[4.1.1.0 ]oct-3-enes. This reaction is also stereospecific, as illustrated for the exo- and e t/o-benzobicycloocta-dienols 43. ... 

The bicyclobutane to buta-1,3-diene rearrangement can be formally regarded as a twofold cyclopropyl to allyl rearrangement ... 

Pudovik, S.L, and Aladzheva, I.M., Acetylene-allene-diene rearrangements of diphosphites with P,Y-acetylenic bond in the entire ester radical, Zh. Obshch. Khim., 33, 708, 1963 J. Gen. Chem. USSR (Engl. Transl.), 33, 702, 1963. 

Metathesis Aikenes or dienes Rearranged aikene(s) or dienes Mo, Re, or Ru... 

Methylenation of 1,3,5-cyclooctatriene at low temperatures gives bicyclo[5.2.0]-nona-2,5-diene suggesting that the expected product, bicyclo[6.1.0]nona-2,6-diene, rearranges via a 3,3-shift under the reaction conditions (Scheme 10.43). " ... 

Only one of the two diastereomers of cw-bicyclo[7.1.0]deca-2,3-diene rearranged upon heating to 250°C in a flow system, and the major product was found to be tricyclo[5.3.0.0 " ]deca-5-ene. The stereochemistries of the reactant and product were reasonably assigned on the basis of the stereoelectronic requirements for... 

Acetoxy-1,4-dienes rearrange regio- and stereo-selectively to 1-acetoxy-2,4-dienes under the influence of palladium(ii) catalysts. Rearrangement, which is complete within a few minutes at room temperature, occurs preferentially at E-disubstituted double bonds, e.g. (143) (144). ... 

The diene (127), prepared by isomerization of the cis,cis-diene, rearranges to (128) the reaction proceeds by a Cope rearrangement through a chair transition state to give (129), followed by a second rearrangement through a boat transition state to the product. ... 

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