Cascade reaction double

The mesoionic compound 41 was further used in a reaction with dimethyl acetylene dicarboxylate (DMAD) to produce a nine-membered cycloadduct 44 which is formed by a reaction cascade of double addition of the alkyne and transannular ring opening of the intermediate 43 (Scheme 7) <20030BC978>. 

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. 

It is very well known that jr-allyl palladium complex 1, which is a key intermediate for the Tsuji-Trost type allylation, has an electrophilic character and reacts with nucleophiles to afford the corresponding allylation products. We discovered that bis 7r-allyl palladium complex 2 is nucleophilic and reacts with electophiles such as aldehydes [27] and imines [28-32] (Scheme 2, Structure 2). We have also shown that bis 7r-allyl palladium complex 2 can act as an amphiphilic catalytic allylating agent it reacts with both nucleophilic and electrophilic carbons at once to produce double allylation products [33]. These complexes incorporate two allyl moieties that can bind with different hapticity to palladium (Scheme 3). The different complexes may interconvert by ligand coordination. The complexes 2a, 2b and 2c are called as r]3,r]3-bisallypalladium complex (also called bis-jr-allylpalladium complex), r)l,r)3-bis(allyl)palladium complex, -bis(allyl)palladium complex, respectively. Bis zr-allyl palladium complex 2 can easily be generated by reaction of mono-allylpalladium complex 1 and allylmetal species 3 (Scheme 4) [33-36]. Because of the unique catalytic activities of the bis zr-allyl palladium complex 2, a number of interesting cascade reactions appeared in the literature. The subject of the present chapter is to review some recent synthetic and mechanistic aspects of the interesting palladium catalyzed cascade reactions which in-... 

The addition of organometals to non-activated carbon-carbon double or triple bonds, although a breakthrough in polymer chemistry about 70 years ago, has now become an efficient way of creating linear or cyclic substituted structures. The new organometallic thus formed can be quenched by various electrophiles, or can be used, in the case of polyunsaturated systems, to create polycycles via cascade reactions. 

However, methylenecyclopropanes with tetrasubstituted double bonds are outstandingly reactive in intramolecular Heck reactions and the particularly strained bicyclopropylidene (7) [53] even surpasses styrene and methyl acrylate in its reactivity, as demonstrated in an interesting cascade reaction of the three partners iodobenzene, bicyclopropylidene (7), and... 

Cooper et al. reported that the cascade reaction of the palladium-catalyzed cyclization and the Barbier-type allylation of the 1,3-diene-aryl iodide 514, the aldehydes 515, and indium gave the heterocycles 516 in good yields (Scheme 154).220b The reaction proceeds through oxidative addition of a C—I bond of 514 to Pd(0) and subsequent insertion of a double bond of 517 to give the jr-allylpalladium intermediate 518. Transmetalation of the jr-allylpalladium 518 with indium leads to the allylindium complex 519, and the following reaction with the aldehydes 515 gives 516. 

A C-radical originated by a yff-fragmentation is able to participate in cascade reactions. For example, a double /9-fragmentation reaction has been described (Eq. 3)... 

The graphitization of diamond may involve thermally-allowed six re-electron concerted processes an electrocyclic reaction converts a six-membered ring in the diamond lattice into three isolated double bonds as shown in Fig. 12. Subsequently, each of the three cyclohexene rings can undergo a retro-Diels-Alder reaction, multiplying the number of double bonds in a triple cascade reaction 23]. 

The use of intramolecular Diels-Alder reactions which use the 2,3-double bond of the indole system as a dienophile appears ideally suited for the synthesis of Aspidosperma and Strychnos alkaloid core structures. In an early example of this approach, Padwa and coworkers [36] first explored the intramolecular cyclization/ rearrangement cascade reaction of the amidofuran derivative 80 as an entry to the tetracyclic core of the Strychnos alkaloids (Scheme 22). After heating 80 at 240°C... 

Double and even triple Heck-Diels-Alder cascade reactions involving bicyclopropyli-dene and 1,4-diiodo- or 1,3,5-triiodobenzene, respectively, have been accomplished. In these sequences, the carbopaUadation across the highly strained alkene is followed by a cyclopropyhnethyl to homoallyl rearrangement with concomitant /3-hydride elimination to yield an allylidenecyclopropane, which subsequently undergoes a smooth [4 + 2] cycloaddition to furnish the spiro[5.2]octene moiety (Scheme 4). ... 

The intramolecular Heck reaction followed by a Diels-Alder cycloadditiont leading to bicyclo[4.3.0]nonene derivatives has been developed into a one-pot cascade reaction.f f Various 2-bromo-l,6-heptadienes including systems with heteroatoms in the tether between the double bonds were cyclized under palladium catalysis producing vicinal exodimethylenecycloalkanes, which reacted with dienophiles (either present... 

The prototypic substrate for intermolecular cascade reactions is norbomene or one of its analogs. Starting from an aryl halide, addition of the formed palladium species to the strained double bond of norbomene yields a norbomylpalladium derivative, which cannot undergo /3-hydride elimination but can accept hydride, for example, from piperidinium formate (Scheme 1) or potassium formate, the latter reaction occurring even at room temperature. 

Bromobenzyl thiopropargyl ethers undergo a microwave-assisted cyc-locarbopalladation-palladium(O) cross-coupling cascade reaction with stan-nanes or boronic acids producing thiochromans with an exocyclic double... 

P.S., and Tilve, S.G. (2009) Cascade wittig reaction-double claisen and cope rearrangements one-pot synthesis of diprenylated coumarins gravelliferone, balsamiferone, and 6,8-diphenylumbelliferone. Tetrahedron Lett, 50,6488-6490. 

A palladium-catalysed double C—H activation using sulfoxide as a traceless directing group has been applied to the regioselective synthesis of polysubstituted diben-zothiophenes through a cascade reaction " by the abstraction of four hydrogen atoms (Scheme 136). 

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