Palladium derivatives cycloaddition

Palladium-Catalyzed Cycloaddition of Benzyne with Allyl Derivatives.141... 

Table 7 Palladium-catalyzed cycloaddition of benzyne with allyl derivatives...

In 1987, Tsuji reported for the first time the racemic palladium-catalysed 1,3-dipolar cycloaddition of vinylcyclopropanes with aryl isocyanates to give the corresponding 5-lactams. ° In 2008, Johnson et al. developed racemic palladium-catalysed cycloadditions of vinylcyclopropanes with aldehydes for the formation of tetrahydrofurans. Inspired by these pioneering results, Kura-hashi and Matsubara have recently developed nickel-catalysed 1,3-dipolar cycloaddition of vinylcyclopropanes with imines to give regioselectively the corresponding substituted pyrrolidine derivatives. As shown in Scheme 1.15,... 

Vinyloxetanes 153 also undergo the palladium catalyzed cycloaddition reaction with carbodiimides to give 4-vinyl-l,3-oxazin-2-imine derivatives 154 " . ... 

Catalytic [2+2+2] cycloaddition of diyne 2.42 to allenes (Scheme 2.59, route (b) leads to cyclic condensed methylencyclohexadienes 2.169, which are often isomerized to the corresponding benzene derivatives Cycloaddition of diyne 2.42 with alkenes route (c) leads to derivatives of 1,3-cyclohexadiene 2.170, which may be used as substrates for further transformations [4]. Different transition metals M such as ruthenium, palladium, rhodium, iridium, nickel, and cobalt were used as catalysts for this reaction. 

For the activation of a substrate such as 19a via coordination of the two carbonyl oxygen atoms to the metal, one should expect that a hard Lewis acid would be more suitable, since the carbonyl oxygens are hard Lewis bases. Nevertheless, Fu-rukawa et al. succeeded in applying the relative soft metal palladium as catalyst for the 1,3-dipolar cycloaddition reaction between 1 and 19a (Scheme 6.36) [79, 80]. They applied the dicationic Pd-BINAP 54 as the catalyst, and whereas this type of catalytic reactions is often carried out at rt or at 0°C, the reactions catalyzed by 54 required heating at 40 °C in order to proceed. In most cases mixtures of endo-21 and exo-21 were obtained, however, high enantioselectivity of up to 93% were obtained for reactions of some derivatives of 1. 

The reactions of nitrones constitute the absolute majority of metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions. Boron, aluminum, titanium, copper and palladium catalysts have been tested for the inverse electron-demand 1,3-dipolar cycloaddition reaction of nitrones with electron-rich alkenes. Fair enantioselectivities of up to 79% ee were obtained with oxazaborolidinone catalysts. However, the AlMe-3,3 -Ar-BINOL complexes proved to be superior for reactions of both acyclic and cyclic nitrones and more than >99% ee was obtained in some reactions. The Cu(OTf)2-BOX catalyst was efficient for reactions of the glyoxylate-derived nitrones with vinyl ethers and enantioselectivities of up to 93% ee were obtained. 

An intramolecular palladium-catalyzed tandem cyclization of dienamides 67 in which the amide nucleophile adds twice has been developed (equation 29)60. This reaction constitutes a formal [4+1] cycloaddition and provides a new route to pyrrolizidine and indolizidine alkaloids. Reaction of dienamides 67 in the presence of catalytic amounts of Pd(OAc)2 and CUCI2/O2 as the oxidant afforded bicyclic compounds 68 in good yields. The pyrrolizidine derivative 68 (R = Me, n = 1) was transformed to the alkaloid ( )-heliotridane. 

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... 

Similar to furo derivatives, cascade ketene imine [2-f2] cycloaddition and palladium catalyzed cyclization gives thieno benzazepines 98 and 99 (X = S) with the fused /i-lactam moiety in 65 and 66% yields, correspondingly (Scheme 18, Section 2.1.2 (1995TL9053)). 

The palladium-phosphine-catalyzed cycloaddition reactions of vinyloxetanes 530 with aryl isocyanates or diaryl-carbodiimides led to 4-vinyl-l,3-oxazin-2-ones 531 or l,3-oxazin-2-imines 532, respectively (Scheme 101). In the absence of phosphine ligands (PPhs, bis(diphenylphosphino)ethane (DPPE), l,3-bis(diphenylphosphino)propane (dppp), no conversion of heterocumulenes was observed. Starting from fused-bicyclic vinyloxetanes, both types of cycloadditions proceeded in a highly stereoselective fashion, affording only the r-isomers of alicycle-condensed 1,3-oxazine derivatives <1999JOC4152>. 

Furukawa and co-workers (368,369) succeeded in applying the softer dicationic Pd-BINAP 260 as a catalyst for the 1,3-dipolar cycloaddition between 225 and 241a (Scheme 12.82). In most cases, mixtures of endo-243 and exo-243 were obtained, however, enantioselectives of up to 93% ee were observed for reactions of some derivatives of 225. A transition state structure has been proposed to account for the high selectivities obtained for some of the substrates (368). In the structure shown in Scheme 12.82, the two phosphorous atoms of the Tol-BINAP ligand and the two carbonyl oxygens of the crotonoyl oxazolidinone are arranged in a square-planar fashion around the palladium center. This leaves the ii-face of the alkene available for the cycloaddition reaction, while the re-face is shielded by one of the Tol-BINAP tolyl groups. 

Methylidenecyclopropanes were converted in a formal [3+2] cycloaddition both to fiirane and pyrrole derivatives. Their reaction, in the presence of a suitable palladium catalyst, with a carbonyl group led to the construction of a tetrahydrofiirane ring (3.92.),117 The analogous reaction in... 

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