Palladium catalysis cycloaddition

Keywords Absolute configuration. Amino acids, Bicyclopropylidene, Coupling reactions. Cycloadditions, Cyclopropanation, Cyclopropanes, Organolithium derivatives. Palladium catalysis. Radical reactions. Small ring polycycles, Spiro compounds. Strain energy. Sulfides... 

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... 

Keywords 1,3-Dipolar cycloadditions 6jr-Electrocydizations Cross coupling Diels-Alder reactions Palladium catalysis... 

The highly strained and thns unnsually reactive tetrasubstituted alkene bicyclopropylidene also turned out to cleanly undergo cocyclizations under palladium catalysis. The TMM species generated from 50 underwent formal [3 + 2] cycloadditions onto electron-deficient (Scheme 14) as well as strained alkenes (Scheme 15).[ ... 

Simple 1,3-dienes such as 1,3-butadiene, isoprene, and related compounds undergo efficient metal-catalyzed oligomerization. Under palladium catalysis, diene dimerization is the most common oligomerization reaction observed. Four modes of dimerization have been reported (Scheme 1) (i) [2 + 2] cycloaddition to afford 1,2-divinylcyclobutane (1) (ii) [4 -I- 2] cycloaddition to afford 4-vinylcyclohexene (2) (iii) [4 + 4] cycloaddition to afford 1,4-cyclooctadiene (3) and (iv) linear dimerization to afford 1,3,7-octatriene (4). 

Palladium catalysis has become an important tool in synthesis due in large part to its ability to mediate a number of different fundamental transformations with low reaction barriers. These include oxidative addition and reductive elimination reactions, insertion and de-insertion (often (3-hydride elimination), nucleophilic ligand attack, or cycloaddition (Scheme 6.1). 

An alternative approach to multicomponent heterocycle synthesis involves the use of palladium catalysis to construct keto-alkynes for cycloaddition reactions. Muller has demonstrated the power of this approach in the construction of a range of aromatic heterocycles. For example, the palladium-catalyzed coupling of acid chlorides with terminal alkynes provides a method to assemble 36. The trapping of this substrate can provide routes to aromatic heterocycles. As an example, the addition of amidines provides a multicomponent synthesis of pyrimidines (Scheme 6.69) [97]. This same substrate 36 is available via the carhonylative coupling of aryl halides with terminal alkynes, providing a four-component synthesis of pyrimidines (98j. 36 can also be employed in 1,3-dipolar cydoaddition reactions. For example, cydoaddition... 

The a-allylpalladium intermediate 135a, which must be formed on coupling of l,3-dicyclopropyl-l,2-propadiene (134), with, for example, iodobenzene under palladium catalysis rapidly undergoes rearrangement to the homoaUylpalladium species 135b and subsequent P-hydride elimination to yield the 1,3,5-hexatriene 136 [152g,h]. This in turn undergoes [4 + 2] cycloaddition with an added dienophile to furnish the 3-(2-cyclopropyl-l-phenyl)cyclohexene derivatives 138 as a mixture of trans,trans- and ds,trows-diastereomers (Scheme 8.31). 

Catalytic Reactions under Palladium Catalysis. PdCl2 (PPh3)2 catalyzes [4 + 2] cycloaddition of 1,1-dimethylsilacyclobutane with dimethyl acetylenedicarboxylate to give the... 

In their synthesis of the naturally occurring product loganin, Trost and co-workers prepared bicycle 87 as a key intermediate. Exposure of substrate 85 to cyclopentenone 86 under palladium catalysis, furnished the desired [3 + 2] cycloaddition adduct 87 in moderate yield. ... 

In this chapter we described [2 + 2 + 2] and related cycloaddition reactions using palladium, iron, manganese, rhenium, and other transition metals. Palladium complexes are able to catalyze [2 + 2 + 2] and related cycloaddition reactions, which proceed via cascade-type mechanism or metallacycle intermediates. It is worthy of note that arynes are suitable substrates for this palladium catalysis. Iron complexes are promising catalysts for practical [2 + 2 + 2] cycloaddition reactions, owing to their low cost and nontoxicity, although both catalytic activity and substrate scope are not satisfactory. Manganese and rhenium complexes allow the use of 3-keto esters as a cycloaddition partner. To realize the practical process and broaden the product scope, further development of new transition-metal catalysts is expected in this research field. 

A Pd-catalyzed method for generating indole-2,3-QDMs 84 from a-phosphonoenecarbamates 83 via the intramolecular Heck reaction was developed by Fuwa and Sasaki [41]. The resulting indole-2,3-QDMs could readily be trapped in situ by such electron-deflcient dienophiles as methyl acrylate, acrylonitrile, and A-methylmaleimide to afford the respective tetrahydrocarbazoles 85 (Scheme 28.29). They also developed an efficient approach to indole-2,3-QDMs from Af-(o-iodoaryl)allenamides 86 under the palladium catalysis, being utilizable for [4 -I- 2] cycloaddition with dienophiles [42]. 

The [2+2] cycloaddition of a ketene and an imine leading to P-lactams can be accomplished using palladium catalysis. Starting from an allyl phosphate or allyl chloride (see also 1), carbonylation with carbon monoxide lead to an intermediate ketene that cycloadds to imines to form the desired P-lactams (Scheme 5-176). ... 

As another example leading to novel conformationally restricted peptidomimetics, a Pd-catalysed enyne cycloisomerization was described as a route to macrocyclic diene structures (119, Figure 11.13, site of ring closure and palladium species indicated). Subsequent [4+2] cycloadditions with dienophiles then gave the target molecules. An interesting application of the use of palladium catalysis in macrocyclization was reported by Barnickel and... 

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