Single palladium catalyzed reaction

In spite of these first successful results, so far Stille cross-couplings have rarely reported employing functionalized stannylated allenes such as easily available donor-substituted allene 80a or allenyl esters such as 81 (Scheme 14.19) [19, 41, 42]. A single palladium-catalyzed annulation reaction with 80b as precursor leading to an a-pyrone derivative was reported [43],... 

A single reaction has been described in which a palladium-catalyzed reaction was employed to form an alkyne [45], Thus, attempted alkylation of carbonate 145 with dimethyl malonate in the presence of Pd(PPh3)4 gave a mixture of enyne 87 and the alkylation product 86 in a 15 1 ratio (Scheme 14.37). Methoxide caused an elimination in (jT-allyl)palladium intermediate 146, which is apparently faster under these conditions than a reaction with the nucleophile (cf. Eq. 14.9). The synthetic importance of this process seems to be limited. 

Palladium-catalyzed reaction of bromo dienes 39 was complete after a few hours, and afforded spirocycles 40a and 40b as single regio- and stereoisomers (Scheme 12). The Heck spirocyclization reaction is regioselective, giving five-membered heterocycles. In addition, it is stereoselective because the Heck adducts were obtained as single geometric isomers [60]. 

The /V-arylalion of certain azoles can be conducted using palladium catalysts. The analogous reactions of pyrazoles and imidazoles have not been reported, and palladium-catalyzed reactions of these azoles with two nitrogens may never compete with classic UUmann chemistry with copper catalysts. However, azoles containing a single nitrogen atom are suitable substrates for palladium-catalyzed IV-arylations. 

The palladium-catalyzed hydrothiolation of terminal alkynes has been achieved using a metallocycle catalyst that was generated through the treatment of palladium acetate with phosphinic acids (Scheme 5.53) [79], Using this catalyst system, benzenethiol was added to 1-octyne in moderate yield with high selectivity for the Markovnikov-isomer. While only a single hydrothiolation example was reported, this chemistry provides the foundation for the design of additional palladium-catalyzed reactions. 

When the products are partially or totally miscible in the ionic phase, separation is much more complicated (Table 5.3-2, cases c-e). One advantageous option can be to perform the reaction in one single phase, thus avoiding diffusional limitation, and to separate the products in a further step by extraction. Such technology has already been demonstrated for aqueous biphasic systems. This is the case for the palladium-catalyzed telomerization of butadiene with water, developed by Kuraray, which uses a sulfolane/water mixture as the solvent [17]. The products are soluble in water, which is also the nucleophile. The high-boiling by-products are extracted with a solvent (such as hexane) that is immiscible in the polar phase. This method... 

A single-mode microwave procedure has been reported for the palladium-catalyzed preparation of both aryl and vinyl nitriles from the corresponding bromides. The reaction times were short and full conversions were achieved in just a few minutes (Eq. 11.33) [50], The cycloadditions to yield the tetrazoles needed slightly longer reaction times, from 10 to 25 min, but only 20 W of power was required as a temperature of 220 °C was reached after 10 min heating. The yields in this step ranged from 36% to 96%. This method for transforming halides into tetrazoles has been used for the synthesis of a novel HIV-protease inhibitor [50],... 

An intramolecular palladium-catalyzed cycloisomerization of enyne 170 was used to access the antifungal agent, chokol C (Scheme 43).102 The choice of ligand and catalyst was essential to the efficiency of the Alder-ene reaction. Enone 171 was obtained as a single olefinic isomer resulting from migration of only Ha during the cycloisomerization reaction. 

As an extension of the Heck reaction, Pd-catalyzed hydroarylation of alkynes and alkenes continnes to attract high level of research interest in simple couphng processes and in cyclization reactions. The use of this type of transformation as part of a domino reaction will be of increasing interest. The research in the field of domino reactions is attracting considerable attention in synthetic organic chemistry since it enables the rapid assembly of complex molecirles in one-pot processes. Very elegant examples of palladium-catalyzed cascade processes where a single catalytic cycle entails several sequential bond transformations have been recently reported [la, b, 2a, b, c]. 

By 1984, the palladium-catalyzed aUyhc alkylation reaction had been extensively studied as a method for carbon-carbon bond formation, whereas the synthetic utility of other metal catalysts was largely unexplored [1, 2]. Hence, prior to this period rhodium s abihty to catalyze this transformation was cited in only a single reference, which described it as being poor by comparison with the analogous palladium-catalyzed version [6]. Nonetheless, Yamamoto and Tsuji independently described the first rhodium-catalyzed decarboxylation of allylic phenyl carbonates and the intramolecular decarboxylative aUylation of aUyl y9-keto carboxylates respectively [7, 8]. These findings undoubtedly laid the groundwork for Tsuji s seminal work on the regiospecific rho-... 

Erb W, Neuville L, Zhu JP (2009) Ugi-post functionalization, from a single set of Ugi-adducts to two distinct heterocycles by microwave-assisted palladium-catalyzed cyclizations tuning the reaction pathways by ligand switch. J Org Chem 74 3109-3115... 

An efficient synthesis of functionalized carbazoles was developed by the palladium-catalyzed annulation of a variety of internal alkynes. This reaction involves arylpalladation of the alkyne, followed by intramolecular Heck olefination, and double bond isomerization. The iodoindole 588 reacts with the alkyne 589 in the presence of a catalytic amount of palladium(O) to give substituted carbazoles 590. In this reaction two new C-C bonds are formed in a single step. Higher reaction temperatures were necessary due to the low reactivity of the iodoindole (566) (Scheme 5.29). 

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