Palladium-promoted reaction

A useful palladium-promoted reaction on an intact pyrrolidone is illustrated in Scheme 27 in which a 1-vinyl derivative is arylated to give both 1-and 2-isomers.55 Compounds of type 24 may prove to be useful precursors for the synthesis of pharmacologically valuable 2-arylethylamines. A related palladium-catalyzed process is described in the section on furans. (see Eq. 14 in Section IV,B,1). 

The formation of carbon-carbon bonds by palladium-promoted reactions has been widely used in organic synthesis [114-116]. A major advantage is that most of these coupling reactions can be performed with catalytic amounts of palladium. Palladium(II)-catalyzed reactions, e.g., the Wacker process, are distinguished from palladium(O)-catalyzed reactions, e.g., the Heck reaction, since they require oxidative regeneration of the catalytically active palladium(II) species in a separate step [117]. Several groups have applied palladium-mediated and -catalyzed coupling reactions to the construction of the carbazole framework. 

The complementary nature of the purely basic and the palladium-assisted alkylation in combination with the chemoselective epoxidation of either of the two double bonds of 2-phenylsul-fonyl-1,3-dienes102 makes these substrates useful synthons for multicoupling reactions. By changing the order of nucleophilic addition and epoxidation, three isomers of the alkylated hydroxy vinyl sulfone are available one of them, that depicted, by palladium-promoted reaction. Without sodium hydride, or in the absence of a nucleophile, / -hydride elimination to the corresponding dienol occurs. 

Recently, palladium complexes of carbene ligands have been recognized as highly reactive catalysts for palladium-promoted reactions, in particular for the Heck reaction [42-44]. The polymer-supported palladium carbene complexes 18 and 19 were prepared by the nucleophilic substitution of the bromomethy-lated Wang resin with 17 under basic reaction conditions (Scheme 7) [45]. The catalytic activity of 18 and 19 was examined for the Heck reaction of aryl bromides with acrylates or styrene to exhibit high TONs up to 5,000. The polymer-supported palladium-carbene complexes are air-stable and recyclable. 

The treatment of carbonyl compounds with Sml2 and methyl chloroformate in the presence of molecular sieves affords the cyclic carbonates or biscarbonates of pinacols. This one-pot reaction proceeds rapidly even with aliphatic ketones. The stereochemistry of the reaction run by this procedure is different from that of conventional pinacolic couplings. Trifluoromethylated five-membered cyclic carbonates were prepared through the palladium-promoted reaction of tertiary trifluoromethylated propargylic alcohols and sodium carbonate (Scheme 6). ... 

The substrate scope of the SEGPHOS-palladium promoted reactions proved to be very restricted, however. This motivated the search for new catalytic systems and the design of more appropriate phosphorus ligands. Thus, Ci-symmetric PN ligands, L5a, which combine axially chiral binaphthylphosphine and chiral... 

The palladium-promoted conversion of 1,3-dienes to pyrroles proceeds via 4-acetoxy-2-alkenylpalladium complexes (Scheme 50g) (81CC59), and a similar pathway may be involved in the palladium mediated reaction of but-2-ene-l,4-diol with primary amines to give A-substituted pyrroles (74CC931). 

Primary (R = H) and secondary aromatic amines react with alkenes in the presence of thallium(III) acetate to give vie- diamines in good yields. " The reaction is not successful for primary aliphatic amines. In another procedure, alkenes can be diaminated by treatment with the osmium compounds R2NOSO2 and R3NOSO (R = t-Bu)," analogous to the osmium compound mentioned at 15-51. The palladium-promoted method of 15-51 has also been extended to diamination. " Alkenes can also be diaminated indirectly by treatment of the aminomercurial compound mentioned in 15-51 with a primary or secondary aromatic amine. 

Tsuji, J. Applications of Palladium-Catalyzed or Promoted Reactions to Natural Product Syntheses. 91, 29-74 (1980). 

An initial step of orthometallation probably also occurs when aniline is allowed to react with ethylene in the presence of a rhodium(I) catalyst. 2-Methylquinoline (10 turnovers relative to the metal) and JV-ethylaniline (30 turnovers) are formed after 72 h in what are probably two independent reaction pathways (Scheme 144).216 It is interesting to note that the intramolecular cyclization step in the proposed216 mechanism (Scheme 144) has precedent in the palladium-promoted quinoline synthesis reported by Hegedus et al.16 (see Scheme 142), but the transformation 118->119 is unusual in the chemistry of organometallic insertion reactions.106... 

Oxazolines can be obtained by the Lewis acid catalyzed epoxide ring opening of glycidic esters or amides (e.g., 118) with acetonitrile . Oxazolidines are available from the palladium-catalyzed cycloaddition of vinyl epoxides with imines <00H885> or the samarium-promoted reaction of ketimines (e.g., 120) with unfunctionalized... 

One of the earliest syntheses of lavendamycin methyl ester, however, did not employ either the Pictet-Spengler or the Bischler-Napieralski reactions for construction of the /J-carboline ring system. Instead, a palladium-promoted ring closure of aryl pyridine 36 (Fig. 12) was used to prepare /1-carboline 37 by Boger and coworkers [35]. Unfortunately, stoichiometric palladium was found to be necessary, in this case 1.5 equivalents of the tetrakis(triphenylphosphine)palladium(0) being used. Friedlander condensation with aldehyde 38 in the presence of benzyltrimethylammonium hydrox-... 

P-Phenylation of a,p-unsaturated ketones in high yield (75-85%), using the palladium catalysed reaction with phenylmercury(II) chloride or tetraphenyltin(IV), is promoted by tetra-n-butylammonium chloride [37],... 

When sodium ethoxide is used in place of sodium hydroxide in the carbonylation reaction of benzyl halides with dicobalt octacarbonyl, ethyl esters are produced instead of the acids [15], Esters are also produced directly from iodoalkanes through their reaction with molybdenum hexacarbonyl in the presence of tetra-/i-butylammo-nium fluoride [16]. Di-iodoalkanes produce lactones [16]. The reaction can be made catalytic in the hexacarbonyl by the addition of methyl formate [16]. t-Butyl arylacetic esters are produced in moderate yield (40-60%) under phase-transfer catalytic conditions in the palladium promoted carbonylation reaction with benzyl chlorides [17]. 

For further details of this reaction, the reader is referred to Chapter 9. The catalytic allylation with nucleophiles via the formation of Ti-allyl metal intermediates has produced synthetically useful compounds, with the palladium-catalyzed reactions being known as Tsuji-Trost reactions [31]. The reactivity of Ti-allyl-iridium complexes has been widely studied [32] for example, in 1997, Takeuchi idenhfied a [lrCl(cod)]2 catalyst which, when combined with P(OPh)3, promoted the allylic alkylation of allylic esters 74 with sodium diethyl malonate 75 to give branched... 

T. Forngren, Y. Andersson, B. Lamm, B. Langstrom, Synthesis of [4-F-18]-1-bromo-4-fluorobenzene and its use in palladium-promoted cross-coupling reactions with organostannanes, Acta Chem. Scand. 52 (1998) 475-479. 

It has so far been known that the allyiic alkylation of unsymmetrical substrates catalyzed by copper complexes proceeds with a high S sr2 regioselectivity contrary to the palladium-catalyzed reactions. However, the corresponding enantioselective version of this reaction has been less developed, in sharp contrast to the copper-promoted asymmetric Michael addition to a,/ -unsaturated systems. 

---