Tandem olefin-migration

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. 

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. 

Fig. 8.125 ln(OAc)3-enhanced Ru-catalyzed tandem olefin migration and aldol reaction. 

In the ruthenium-catalyzed tandem olefin migration of 3-buten-2-ol and aldol reaction with aryl aldehydes, catalytic In(OAc)3 was found to be essential to elevate the poor yields to moderate and good levels [278] (Figure 8.125). Similar results were observed for the same reaction in ionic liquids [279]. 

A tandem RCM-alkene isomerization sequence to form 5-, 6-, and 7-membered enol ethers was reported by Snapper and co-workers <02JA13390> (Scheme 36). In this process the RCM reaction is run under an atmosphere of 95 5 N2.TI2 to convert the intermediate ruthenium alkylidene into an olefin-isomerization catalyst. Note that alkene migration can convert isomeric metathesis products into the same 2,3-enol ether. A single example of the formation of a 6-membered tosyl enamide was reported in this manuscript. 

Two approaches to tandem formation of copolymer nanocomposites (a) immobilization of the oligomerization catalyst, resulting in expansion of the clay layers during formation of a-olefins and (b) immobilization of the copolymerization catalyst, resulting in exfoliation of the clay by migration of the a-olefins into the interlayer spaces. 

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