Cascade reactions synthesis

Multistep Cascade Reactions Synthesis of Bis-1,3,4-thiadiazolo-1,3,5-triazinium Halides... 

Hulot, C., Amiri, S., Blond, G. L, Schreiner, P. R., Suffer , J. (2009). Understanding the torquoselectivity in 8x-electrocyclic cascade reactions synthesis of fenestradienes versus cyclooctatrienes. Journal of the American Chemical Society, 131, 13387-13398. 

Hao, L., Teck-Peng, L. (2008). Control of up to five stereocenters in a cascade reaction synthesis of highly functionalized five-membered rings. Journal of the American Chemical Society, 130, 7194-7195. 

Ma, G., Afewerki, S., Deiana, L., Palo-Nieto, C., Liu, L., Sun, J., Ibrahem, I., Cordova, A. (2013). A palladium/chiral amine co-catalyzed enantioselective dynamic cascade reaction synthesis of polysubstituted carbocycles with a quaternary carbon stereocenter. Ange-wandte Chemie International Edition, 52, 6050-6054. 

The known, in many cases very special, synthetic approaches to azocines often proceed via valence isomerization of appropriate precursor molecules. In this section these routes are classified by the last step in the reaction cascade. The synthesis and chemistry of azocines has been described in several excellent reviews,9-11 so that the treatment here is systematic and rather concise. 

Nicolaou, K.C., Edmonds, D.J., Bulger, P.G. (2006) Cascade Reactions in Total Synthesis. Angewandte Chemie International Edition, 45, 7134-7186. 

The same concept of using mutually interfering acid and base catalysts was achieved by Frechet s group through the use of star polymer systems [30]. The synthesis of the catalysts is outlined in Scheme 5.13. The arms of the star polymers prevent the catalysts from interfering with each other and allow the cascade reaction to proceed unhindered. 

Poessl, T.M., Kosjek, B., Ellmer, U. et al. (2005) Non-racemic halohydrins via biocatalytic hydrogen-transfer reduction of halo-ketones and one-pot cascade reaction to enantiopure epoxides. Advanced Synthesis and Catalysis, 347 (14), 1827-1834. 

A systematic exploration of the intramolecular [4+2]/[3+2] cycloaddition cascade of 1,3,4-oxadiazoles was described. The studies permit the use of unsymmetrical dienophiles, dipolarophiles, and oxadiazoles as well as to control the cycloaddition regioselectivity and diastereoselectivity. The scope and utility of the reaction were defined <2006JA10589>. The tandem intramolecular [4+2]/[3+2] cycloaddition cascade reaction of 1,3,4-oxadiazole was applied to the syntheses of a series of natural products including a total synthesis of (-)- and ent-(+)-vindoline <2006JA10596>. 

In some cases, the reaction (4—> 5) can be combined with the synthesis of starting AN (4) from simpler molecules. As mentioned above, there are no general methods for the synthesis of AN (4). Several most commonly used schemes for the synthesis of functionalized AN (4) are given below (most often, there are cascade reactions). 

Et3B-induced radical cascade reactions with 1,5-enynes and 1,5-diynes have been applied to the synthesis of dioxatriquinanes and tricyclic glucocon-jugates (Scheme 17) [44,45]. Some of these elegant cascade cyclizations were also performed under mild conditions at - 50 °C. 

Cascade Addition-Cyclization Reactions Given the importance of cascade reactions in modem chemical synthesis, the MacMillan group has proposed expansion of the realm of iminium catalysis to include the activation of tandem bond-forming processes, with a view toward the rapid constraction of natural products. In this context, the addition-cyclization of tryptamines with a,p-unsaturated aldehydes in the presence of imidazolidinone catalysts 11 or 15 has been accomplished to provide pyrroloindoline adducts in high yields and with excellent enantioselectivities (Scheme 11.3a). This transformation is successful... 

Keywords Absolute configuration, Amines, Amino acids, Carbenes, Cascade reactions, 2-chloro-2-cyclopropylideneacetates. Combinatorial libraries. Cycloadditions, Cyclobutenes, Cyclopropanes, Diels-Alder reactions. Heterocycles, Michael additions. Nitrones, Nucleophilic substitutions, Peptidomimetics, Palladium catalysis. Polycycles, Solid phase synthesis, Spiro compounds. Thiols... 

So-called domino or cascade reactions have become more and more important for the efficient synthesis of complex organic molecules [1211. In this respect methyl 2-chloro-2-cyclopropylideneacetate (1-Me) has been used as a dieno-phile to trap cyclic dienes which were produced by intramolecular Heck reactions in Diels-Alder cycloadditions. Thus, the spirocyclopropanated functionalized bicyclo[4.3.0lnonenes 248,250 (Fig. 11) were obtained from the bromo-diene 247 or enynes 249 in 56-83% yield (Scheme 71) [122,1231. 

Bowman et al. reported the total synthesis of ellipticine (228) involving an imidoyl radical cascade reaction (730). For this key step, the required imidoyl radical was generated from the imidoyl selanide 1290, which was obtained from ethyl 2-(4-pyridyl)acetate (1286). Reaction of 1286 with LDA, followed by addition of methyl iodide, led to the corresponding methyl derivative 1287. Treatment of 1287 with 2-iodoaniline (743) in the presence of trimethylaluminum (AlMes) afforded the amide 1288. Using Sonogashira conditions, propyne is coupled with the amide 1288 to afford the aryl acetylene 1289. The aryl acetylene 1289 was transformed to the... 

Chemoenzymatic polymerizations have the potential to further increase macro-molecular complexity by overcoming these limitations. Their combination with other polymerization techniques can give access to such structures. Depending on the mutual compatibility, multistep reactions as well as cascade reactions have been reported for the synthesis of polymer architectures and will be reviewed in the first part of this article. A unique feature of enzymes is their selectivity, such as regio-, chemo-, and in particular enantioselectivity. This offers oppormnities to synthesize novel chiral polymers and polymer architectures when combined with chemical catalysis. This will be discussed in the second part of this article. Generally, we will focus on the developments of the last 5-8 years. Unless otherwise noted, the term enzyme or lipase in this chapter refers to Candida antarctica Lipase B (CALB) or Novozym 435 (CALB immobilized on macroporous resin). 

For the synthesis of furanones, Kirsch et al. studied the gold-catalyzed hetero-cyclization/1,2-migration cascade reaction of a-hydroxy propargyl ketones [139]. 

Meijere et al. [117] group have investigated the direct synthesis of 3-spiro-cyclopropanated p-lactams 184 (Scheme 43) using novel three-component cascade reaction. Earlier, Alberto Brandi and coworkers [118-120] have applied nitrones 181 and bicyclopropylidene 182 to obtain cylcoadducts 183, which were further fragmented under acidic conditions to afford spiro-p-lactams 184. However, this reaction required longer reaction time for the formation of cycloadducts 183. 

A related one-pot, three-component synthesis of fi-amino carbonyl compounds has been achieved using a cascade reaction of anilines with aromatic aldehydes and car- (g) bonyl compounds, catalysed by zinc triflate.19... 

For exhaustive illustrations of Pd-mediated cascade reactions, see (a) Negishi, E.-I., ed. Handbook of Organopalladium Chemistry for Organic Synthesis, Vols. 1 and 2 J. Wiley Sons, Chichester, 2002 (b) Tsuji,... 

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