Tandem olefination

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). 

Grubbs has reported a similar tandem olefin metathesis-carbonyl olelination process for the preparation of cyclic olefins [31]. In this case, treatment of a keto-olefin with the molybdenum alkylidene 1 at 20°C generates an intermediate alkylidene complex. Under these conditions, competing intermolecular olelination does not occur. However, intramolecular carbonyl olelination of the initially formed alkylidene complex can occur and this results in the formation of a cyclic olefin. This tandem sequence is illustrated by the transformation of keto-olefins... 

Azabicyclononenecarboxylate acylated with unsaturated carboxylic acids is converted via tandem olefin metathesis in indolizidine scaffolds <2006OL5553>. 

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. 

Grubbs reported tandem olefin metathesis/hydrogenation as a means to make satnrated cyclic prodncts and a one-pot RCM/transfer dehydrogenation/hydrogenation ronte to (R)-(-)-Mnscone utilizing (4a) (Scheme 19). Snapper and coworkers took advantage of the isomerization side reaction... 

This new procedure makes use of an alternative building block for the cycloaddition step, namely, ethyl 2-(hydroxymethyl)acrylate (7), which can be easily prepared via a known [22] tandem olefination/Baylis-Hillman sequence (Scheme 16.4) from commercially available and inexpensive triethyl phosphonoacetate (6), paraformaldehyde and potassium carbonate as the base, in water at 40 °C for 1 h [23]. 

Kawasaki. T, Terashima, R., Sakaguchi, K.-E., Sekiguchi, H., and Sakamoto, M., A short route to reverse-prenylated pyrrolo[2,3-7>]indoles via tandem olefination and Claisen rearrangement of 2-(3,3-dimethyl-allyloxy)indol-3-ones. First total synthesis of flustramine C, Tetrahedron Lett., 37, 7525, 1996. Nasutavicus, W.A., Tobey, S.W., and Johnson, E, The cyclization of nitriles by halogen acids. Part 2. A new synthesis of substituted S/Z-azepines, J. Org. Chem., 32, 3325, 1967. 

Kawasaki, T., Terashima, R., Sakaguchi, K. et al. (1996) A short route to reverse-prenylated pyrrolo[2,3-h]indoles via tandem olefination and Claisen rearrangement of 2-(3,3-dimethyl-aUyloxy)indol-3-ones First total synthesis of flustramine C. Tetrahedron Letters, 37, 7525-7528. 

Very recently, the enantioselective total synthesis of hexahydropyrrolo[2,3-h]-indole alkaloids, (-)-pseudophynaminol, through tandem olefination, isomerization and asymmetric Claisen rearrangement was reported [81]. Using a 3-ketodi-hydroindole derivative 107, the reaction smoothly proceeded under extremely... 

The molybdenum-alkylidene 9 [130] promoted tandem olefin metathesis-carbonyl olefination of olefinic ketones offers an effective synthetic method for cy-cloalkenes (Scheme 4.56 Table 4.19). The complex 9 initially reacts with the ter-... 

Scheme 4.S6. Formation of cycloalkenes from olefinic ketones by the molybdenum-alkylidene promoted tandem olefin metathesis-carbonyl olefination.

Tab. 4.19. Tandem olefin metathesis-carbonyl olefination promoted by the molybdenum-alkylidene 9.

The same effect has been observed in the case of an encapsulated organogold catalyst of cycloi-somerization of enyne 441 by Scheme 5.23, and it has been attributed [22] to the hydrophobic environment within the coordination capsule 575, preventing carbenium-ionic intermediates of the catalytic process from their side reactions with water. The same caging catalyst has been used in [23] to perform the combined enzymatic and transition metal catalysis of tandem reactions by Scheme 5.24. The authors of this work also developed a tandem olefin isomerization-reduction reaction by Scheme 5.25 with the encapsulated organoruthenium cation as a catalyst on its... 

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]. 

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