Cascade sequence reactions

Malacria and coworkers346 prepared phyllocladane and kaurane types of diterpenes by means of [3 + 2]/[2 + 2 + 2]/[4 + 2] cascade reaction sequences. A representative example of such a reaction sequence has been outlined in equation 171. The five-membered ring of 598 was built by a 1,3-dipolar cycloaddition between 596 and an all-carbon 1,3-dipole generated from 597. The reaction of 598b with 568h afforded benzocyclobutene 599. The intramolecular [4 + 2] cycloaddition afforded diastereomers 600 and 601 in a 5 1 ratio. It is noteworthy that the exocyclic double bond in 598b neither participates in the [2 + 2 + 2] cycloaddition reaction nor isomerizes under the reaction conditions applied. 

Outline the mechanistic pathway for this radical cascade reaction sequence from 1 to 2. 

The usefulness of palladium-based chemistry is highlighted by the multicomponent cascade reaction sequence that uses o-ethylanilines, aryl iodides, primary amines, and carbon monoxide (Equation 99) <2005JOC6454>. 

To further expand the scope of this new silver(I)-mediated reaction sequence, interrupted Nazarov cyclizations were explored using the halocyclopropane chemistry, an investigation that was prompted by the discovery of an intriguing result. It was found that treatment of the phenethyl-substituted compound 76 with 1.5 equiv of silver tetrafluoroborate in dichloromethane provided benzohydrindenone 77 as the sole product, with no apparent formation of the simple a-chlorocyclopentenone (Scheme 4.24). This prompted an examination of appropriately substituted gem-dichlorocyclopropane substrates in analogous interrupted Nazarov processes to ascertain the scope of this new cascade reaction sequence. 

The carbolithiation of unactivated alkenes has also proven very successful for the synthesis of complex polycyclic systems. This has typically been achieved by reaction sequences utilizing an intramolecular carbolithiation process to generate a variety of carbocycles185 and heterocycles186. To achieve the intermolecular carbolithiation reaction required to initiate a controlled cascade reaction sequence for the generation of indole ring scaffold, Kessler and coworkers44 have expanded the synthetic utility of the styrene... 

The roles of Factors V and VIII in the reaction sequence leading to thrombin formation have slowly become known. Both these proteins are very large in size, serve as cofactors in this cascade reaction sequence, and increase by approximately 100 times their cofactor activity upon exposure to minimal concentrations of thrombin. Likewise, both factors are inactivated by a similar mechanism when attacked by activated protein C (Fll). Tans and coworkers utilized synthetic substrate assays specific for Factor Xa and thrombin to demonstrate that both these factors act predominantly by increasing... 

The rate of film oxidation is set by the rate determining step in the cascade reaction sequence. For this system, we have observed that the film oxidation rate essentially follows the hydrogen peroxide generation rate. We can use equations (18.14) and (18.15) for iire [IJ ]o 1 to relate the triiodide flux to the triiodide generation rate and, by equation (18.10), to the bound conjugate so that... 

Coldham et al. reported on a cascade reaction sequences involving condensation, cyclization, intramolecular dipolar cycloaddition for preparation of fused tricyclic heterocycles which can be converted in two steps to a 1,3-oxazine present in some yuzurimine-type Daphniphyllum alkaloids under some conditions [57], In another study, addition of hydroxylamine to substituted 4-chlorobutanals gives intermediate nitrones that imdergo tandem cyclization and then intramolecular dipolar cycloaddition to give the core... 

Kumar and coworkers synthesized the substrate 27 in quantitative yields from the commercially available 3-formylchromones and acetylene carboxylates in two steps [55]. Substrate 27 embodies multiple electrophiUc sites (5+), a vinylogous ester (a leaving group) and a couple of pronucleophUic sites (2 and 2 ) to faciUtate the interplay of diverse cascade reaction sequences (Figure 27.3). 

Af-Benzyl and phenyl hydroxylamines 45 and 46, the mononucleophiles triggered a new cascade reaction sequence (Scheme 27.4) with both 27 leading to... 

An efficient method to prepare l /f-spiro-[indoline-3,3 -quinoline]-2, 4 -diones and their trifluoromethylated products was developed hy Wang and co-workers in 2014. The reaction proceeds via a palladium-catalyzed Sono-gashira coupling-Wacker-type ojqqjalladation-cyclization cascade reaction sequence. The amount of water in the reaction system played an important role in the in situ trifluoromethylation reaction, and the trifluoromethylation exhibited excellent molecular self-induced stereoselectivity. 

SAM and related cofactors, isolated or produced by total synthesis, are highly priced and their stoichiometric consumption requires one or even more equivalents. An economically feasible cofactor-dependent biocatalysis thus rehes on the substoichiometric or even catalytic use of the cofactor associated with a cofactor regeneration system, ideally in a cascaded reaction sequence. Such enzymatic conversions are assisted by an additional recycling reaction which restores the... 

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