Allylic rearrangement, 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. 

Methyl-1,2-dihydropapaverine (175, R = OMe) rearranges to the 2-methyl-3-(3,4-dimethoxybenzyl)-6,7-dimethoxy-3,4-dihydroisoquinolin-ium salt (176, R = OMe) under very mild conditions (treatment with 2% hydrochloric acid). A similar rearrangement of l-(3,4-methyl-enedioxybenzyl) - 2 - methyl - 6,7 - dimethoxyisoquinoline (175, R, R = —O—CHj—O—) affords 3-(3,4-methylenedioxybenzyl)-2-methyl-6,7-di-methoxy-3,4-dihydroisoquinolinium chloride (176, R, R = O—CHj—O—) (256). The reaction was shown to be an allylic rearrangement with internal return (275,275). 

Allylic rearrangements with 3,3,6,6-dj-cyclohexene occurred in 20% of the MMO hydroxylation products compared to 33% for cytochrome P-450. These two experiments suggest that, with M. trichospor-ium OB3b, a rebound reaction must occur with a greater rate constant than with cytochrome P-450, in accord with the radical clock substrate work. 

Mcclanahan RH, Huitric AC, Pearson PG, et al. Evidence for a cytochrome-P-450 catalyzed allylic rearrangement with double-bond topomerization. J Am Chem Soc 1988 110(6) 1979— 1981. 

High levels of asymmetric induction can be achieved intramolecularly if the substrate functionality and the heteroatom ligand are contained in the same molecule. Chiral amido(a]kyl)cuprates derived from allylic carbamates [(RCH= CHCH20C(0)NR )CuR undergo intramolecular allylic rearrangements with excellent enantioselectivities (R = Me, n-Bu, Ph 82-95% ee) [216]. Similarly, chiral alkoxy(alkyl)cuprates (R OCuRLi) derived from enoates prepared from the unsaturated acids and trans-l,2-cyclohexanediol undergo intramolecular conjugate additions with excellent diasteroselectivities (90% ds) [217]. 

Reaction type 6B of Table 10-1 is allylic rearrangement with simultaneous condensation with another molecule. The reaction, which is catalyzed by prenyl-transferases,3073 occurs during the polymerization of polyprenyl compounds (Fig. 22-1,Eqs. 22-2,22-3). Experimental evidence favors a carbocation mechanism for all of these reactions.308 309 See Chapter 22. 

The reaction is very slow in acetic acid alone, and accelerated as acetate by the addition of bases [59]. These two isomers undergo Pd-catalysed allylic rearrangement with each other. 3-Acetoxy-l,7-octadiene (139) is converted to the allylic alcohol 157 and to the enone 158, which is used as a bisannulation reagent [60], Thus Michael addition of 158 to 2-methylcyclopentanedione (159) and aldol condensation give 160. The terminal alkene is oxidized using PdCl2/CuCl/02 to the methyl ketone 161. After reduction of the double bond in 161, aldol condensation affords the tricyclic system 162. 

Methylglyoxalacetal (21) is obtained from acetone (39) by oxidation with methyl nitrite in the presence of methanol and an acid catalyst. Ethynylation and partial hydrogenation yield 2-hydroxy-2-methyl-but-3-enal-dimethylacetal (27), which, after acetylation, yields the P-formylcrotyl acetate (8 b)34 via a copper-catalyzed allyl rearrangement with subsequent hydrolysis. 

Chloro compound 112, when treated with sodium methoxide, is methox-ylated at the ring (113) if an ortho methyl group is present, this is methox-ylated to give 114. This transformation is considered to be an allylic rearrangement with participation by 7r-electrons of the heteroaromatic system (84M1171). 

Another fascinating, unique property of allylic systems is their propensity for allylic rearrangement with transfer of functionality from one end of the allylic system to the other and concomitant double bond shift with or without transformation of functional groups. In the latter case (X = Y equation 1) a reaction is synthetically useful only in unsymmetrical cases for a 1,3-transposition of the functional group. 

Reaction with unsaturated compounds (reviews Kharasch,Sosnovsky,andYang reported that, in the presence of a catalytic amount of a copper or cobalt salt, t-butyl perbenzoate reacts with an olefin to give an allylic benzoate with no allylic rearrangement with a terminal olefin the only product isolated was the allylic ester with a terminal double bond. A further example is the reaction with 1-methylene-4-f-butylcyclohexane. However, in contrast to these early reports, Kochi found by o... 

Occasionally, gew-dichlorocyclopropanes with phenyl or alkoxy substituents are transformed by strong base in aprotic or (rarely) protic solvents to allylic substitution products that do not obey at all the rules for cyclopropyl to allyl rearrangements with regard to their constitution and configuration. "These reactions are mechanistically distinct. They are usually initiated by base-induced elimination of hydrogen chloride to form phenyl- or alkoxy-substituted cyclopropenes, which are then intercepted by nucleophiles. ° These reactions are discussed in Section 2.B.2.I. Small structural differences can divert the reaction into one or the other reaction channel. Cyclopropane 25 on treatment at — 50°C with 2 equivalents of potassium /er/-butoxide in tetrahydrofuran in the presence of catalytic dicyclohexano-18-crown-6... 

Moreover, poly(trichlorobutadiene)s are known to undergo allylic rearrangements with migration of allylic chlorine (14%) and hydrogen (3-10%) atoms under the action of solvents [38]. This accounts for remarkable similarity of the IR spectra of dehydrochlorinated poly(l,l,2-trichloro-butadiene) and poly(l,2,3-trichlorobutadiene) (Figure 12.1). 

A compound somewhat related to 902, the alcohol 905, has been isolated from peppermint and synthesized from 2,6-dimethyl-5,7-octadien-2-ol (called ocimenol by the authors). The action of peracetic acid on the latter gave the furan 906, and allylic rearrangement with phosphorus tribromide followed by replacement of the bromide with potassium acetate gave the ( ) + (Z) acetates of 905. ... 

On the other hand, when tropone (41) is allowed to react with the phosphaalkynes 9a, 9b, or 9 e at a somewhat raised temperature in the molar ratio 1 1 in toluene, the reaction sequence ends with the formation of the diphosphapentacyclic compounds 45a-c [45]. In other words, this means that the initially formed 43 must have undergone a stereoselective, [8 + 2]-cycloaddition with a second equivalent of tropone (41). The hexacyclic species 44 thus formed experience a cyclopropyl-allyl rearrangement with subsequent [1,5]-H shift and ring inversion, finally to furnish the isolated pentacyclic compounds 45 [45]. The semiempirically... 

The viscidanes exhibit an antipodal configuration at C7 compared to the bisabolane, serrulatane and decipiane diterpenes. This difference may reflect the involvement of a 3/ ,6 -acyclic precursor (211), or 3S,6E-, which cyclizes to the lS,7/ -intermediate (212) (Scheme 51). A 1,2-hydride shift with displacement of X would generate the tertiary carbocation (213) which could alkylate the Re-facc of CIO. The spiro-ring system produced (214) contains the 1,4-trans-disubstitution on the cyclopentane ring observed for the viscidane nucleus. A 1,5-hydride shift of the quasi-a ial allylic hydrogen in 214 and allylic rearrangement, with net yn-addition of water, completes the elaboration of the nucleus. Circumstantial support for the last step can be enlisted... 

---