Migration, olefin

Use of DMF as a solvent for the oxidation of l-o1efins has been reported by Clement and Selwitz. The method requires only a catalytic amount of PdCl2 and gives satisfactory yields under mild conditions. A small amount of olefin migration product is the only noticeable contaminant in the cases reported. The procedure can be applied satisfactorily to various 1-olefins with other functional groups. This useful synthetic method for the preparation of methyl ketones has been applied extensively in the syntheses of natural products such as steroids,macrolides, dihydrojasmone, and muscone. " A comprehensive review article on the palladium-catalyzed oxidation of olefins has... 

In the presence of transition-metal complexes, organic compounds that are unsaturated or strained often rearrange themselves. One synthetically useful transition-metal catalyzed isomerization is the olefin migration reaction. Two general mechanisms have been proposed for olefin migrations, depending on the type of catalyst employed (A and B) (Scheme 3.8).137... 

Recently, Grubbs138 demonstrated that olefin isomerization of allyl-lic ethers and alcohols is catalyzed by Ru(II)(H20)6(tos)2 (tos = p-toluenesulfonate) in aqueous medium. The olefin migration products, enols, and enol ethers thus generated are unstable and are hydrolyzed instantly to yield the corresponding carbonyl compounds (Eq. 3.34). 

It has also been shown that dimethylsilyl enolates can be activated by diisopropylamine and water and exhibit a high reactivity toward iV-tosyl imines to give Mannich-type reaction products in the absence of a Fewis acid or a Bronsted acid.51 For example, the reaction of [(1-cyclohexen-l-yl)oxy]dimethylsilane with 4-methyl-A -(phenylmethylene)benzene sulfonamide gave re/-4-methyl-N- (f )-[(15)-(2-oxocyclohexyl)phenyl-methyl] benzenesulfonamide (anti-isomer) in 91% yield stereoselectively (99 1 anti syn) (Eq. 11.30). On the other hand, Fi and co-workers reported a ruthenium-catalyzed tandem olefin migration/aldol and Mannich-type reactions by reacting allyl alcohol and imine in protic solvents.52... 

Recently, ruthenium-catalyzed tandem olefin migration/aldol-type or Mannich-type reactions have been developed with aldehydes or imines and allylic alcohols (Scheme 74). 

Using a protocol for tandem carbonylation and cycloisomerization, Mandai et al.83 were able to synthesize cyclopentene and cyclohexene derivatives in high yield, including fused and 5/>/>0-bicycles (Scheme 25). The cyclohexene Alder-ene products were not isolable methanol addition across the exocyclic double bond (in MeOH/ toluene solvent) and olefin migration (in BuOH/toluene solvent) were observed. The mechanism of methanol addition under the mild reaction conditions is unknown. In contrast to many of the other Pd conditions developed for the Alder-ene reaction, Mandai found phosphine ligands essential additionally, bidentate ligands were more effective than triphenylphosphine. 

Because olefin migration was very rapid under the conditions used, internal alkenes could be used. Thus, treatment of ( )-2-pentene or ( )-3-pentene with Tf2NH (1.1 eq) and (p-ClC6H4)3P in chlorobenzene at 65 °C for 24 h both gave the 1-pentylphosphonium salt in 91% yields (Scheme 21). The use of mixtures of alkene regioisomers and stereoisomers for the reaction may have a synthetic advantage. 

Now that the a/3-diadsorbed species is known to be tr-complexed olefin, the simplest interpretation of rollover is that the metal-olefin bond breaks the free olefin has then a transient existence in the gas phase and can migrate from one type of site to another. That this occurs to an appreciable extent even at ambient temperatures starting with alkane in excess D2 may seem surprising but is powerful support for the olefin migration step postulated in hydrocracking and hydroreforming on dual-functional catalysts. 

Tandem Olefin-Migration/Aldol- and Mannich-Type Reactions.325... 

Indeed, a ruthenium-catalyzed tandem olefin-migration/aldol-type reaction has been realized when an aldehyde is present in aqueous media [18,19]. For 3-butene-2-ol (9), the tandem isomerization/aldol-type reaction was examined. The mixture of 9, aldehyde (10), and a catalytic amount of RuCl2(PPh3)3 in H20/toluene(4/l) (Eq. 6) or H20 alone (Eq. 7) was stirred for 5 h at 110 °C (oil bath temperature) and afforded the aldol adduct 11. 

Under the same conditions, the yield of the corresponding aldol product was very low (10%) when a-vinylbenzyl alcohol (12) was used instead of 9 to react with benzaldehyde (10a). The allyl alcohol 12 was mainly converted into pro-piophenone, which was attributed to the olefin migration by path b described in Fig. 1. By adding a Lewis acid, In(OAc)3, as a cocatalyst, the aldol reaction was dramatically improved and the yield of 13a was increased from 10% to 80% (Eq.8). 

Higher 1-alkenes reacted more effectively with (/ -ClC6H4)3P than with PPhs or (jc>-tolyl)3P. The reaction of 1-pentene (5 eq), Tf2NH (1.1 eq), and (p-C1C6H4)3P in the presence of the palladium complex (1.0 mol%) gave the 1-pentylphosphonium salt in 91% yield (Scheme 20). The use of 5 eq of 1-pentene was sufficient for this reaction, despite the volatile nature of this compound (bp 30 C), and the rapid olefin migration to form a very small amount of 1-pentene. The reaction of 1-hexene also proceeded effectively giving the 1-hexylphosphonium salt in 88% yield. 

While these catalysts could effect metathesis with similar levels of Z-selectivity, they had lower levels of metathesis activity and caused significant amounts of olefin-migration... 

In the study of Ru-BINAP catalyzed asymmetric hydrogenation of geraniol 10, a striking isomerization to y-geraniol 11 was observed, Eq. (5) [24]. The reaction is noteworthy in that it promotes the olefin migration from an inner to an exo position. Originally the presence of 11 was supposed to be an intermediate... 

For substrates lacking olefinic migrating groups, [1,2]-shifts occur instead to give oxabicydic products, Eq. 46. 

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