Palladium-catalyzed insertion

Denmark and Kallemeyn have described the mild palladium-catalyzed insertion of 1,2-diethoxy-1,1,2,2,-tetra-methyldisilane EtOMe2SiSiMe2OEt into aryl bromides RBr affording aryldimethylsilyl ethers RMe2SiOEt and Me2SiBrOEt in high yields.750 Williams and Tanaka et al. have reported on the palladium- and platinium-catalyzed reaction of carbonyl and imine compounds with disilanes.7... 

Palladium-catalyzed insertion of norbornene into the Si —Sn cr-bond leads exclusively to the adduct which has exo.exo configuration23. 

Using the same procedure as for the synthesis of the related five- and six-membered benzolactams, the benzoazepinone derivatives (27) have been synthesized in good yield. This palladium-catalyzed procedure has more recently been extended to the synthesis of a number of antibiotics. A key step in the synthesis of anthramycin, for example, is the palladium-catalyzed insertion of CO into the amine (28). ... 

Isocyanides undergo palladium catalyzed insertion into the Si—Si bond of disilanes, and, in the case of l,l,2,2-tetramethyl-l,2-disilacyclopentane, ring expansion occurs and the 1,3-disilacyclo-hexane (15) results <87TL1293>. A 1,3-disilacyclohexane may also result from the photolysis of a... 

A 1,2,3,4,5-pentasilacyclohexane derivative has been found to be one of the many products formed in the pyrolysis of polydimethylsilane <9lMi 627-03). Palladium catalyzed insertion of an arylisocyanide into a cyclopentasilane also gives the same ring system <91JA8899> as does the thermally induced isomerization of a pentasilacycloallene derivative <93JA2534>. 

A regioselective three-component domino process involving an initial ring opening of aziridine 151 with 2-iodophenol 152, followed by palladium-catalyzed insertion of isocyanide 153, afforded substituted 1,4-ben-zoxazepines 154 (13ASC3401). 

M. Catellani and G. P. Chiusoli, J. Organomet. Chem., 1983, 250, 509-515. The Termination Step in Palladium-Catalyzed Insertion Reactions. 

Palladium-Catalyzed Insertion of Isocyanides into Si-Si Linkage. A mixture of Me6Si2, aryl isocyanide (24), a catalytic amount of paUadiuin(Il) acetate and toluene is heated to... 

In 2006, Yoshida et al. reported the palladium-catalyzed insertion reaction of o-QDMs into a Sn—Sn o-bond of hexabutyldistannane by use of diphenyl-2-pyridylphosphine as a ligand, giving the distannylation products a,a -bis(tributylstannyl)-c -xylenes 76 (Scheme 28.28) [39]. The reaction of o-QDM bearing a naphthalene backbone or a phenyl moiety afforded good yields of the products, and moreover, a methyl group of a-methyl-o-QDM did not inhibit the course of the distannylation. 

The N-substituted aminoacids required could be prepared by microwave-assisted reductive amination of aminoacid methyl esters with aldehydes, and although in the Westman report soluble NaBH(OAc)3 was used to perform this step, other reports have shown how this transformation can be performed in using polymer-supported borohydrides (such as polymer-supported cyanoborohydride) under microwave irradiation [90]. An additional point of diversity could be inserted by use of a palladium-catalyzed reaction if suitably substituted aldehydes had been used. Again, these transformations might eventually be accomplished using supported palladium catalysts under microwave irradiation, as reported by several groups [91-93]. 

The palladium-catalyzed stannylboration (90) [124] or silylboration (87) [109, 114] succeeds in the intramolecular carbocyclization of diynes and enynes (Scheme 1-27). It is interesting that a very strained four-membered cycUzation of hexa-l,5-diyne proceeds without any difficulties, similarly to five- or six-membered cycUzation. The boryl group is selectively introduced into the more reactive C=CH rather than C=C for enynes and into the terminal C=CH rather than the internal C=CR for diynes, again suggesting a mechanism proceeding through the first insertion into the Pd-B bond in preference to the Pd-Sn or Pd-Si bond. 

This reaction typifies the two possibilities of reaction routes for M-catalyzed addition of an S-X (or Se-X) bond to alkyne (a) oxidative addition of the S-X bond to M(0) to form 94, (b) insertion of alkyne into either the M-S or M-X bond to provide 95 or 96 (c) C-X or C-S bond-forming reductive elimination to give 97 (Scheme 7-21). Comparable reaction sequences are also discussed when the Chalk-Harrod mechanism is compared with the modified Chalk-Harrod mechanism in hydrosily-lations [1,3]. The palladium-catalyzed thioboratiori, that is, addition of an S-B bond to an alkyne was reported by Miyaura and Suzuki et al. to furnish the cis-adducts 98 with the sulfur bound to the internal carbon and the boron center to the terminal carbon (Eq. 7.61) [62]. 

The next task was removal of the C3,C3 -esters. Although the palladium-catalyzed decarboxylation protocol performed well in previous systems, a competing C-H insertion reaction was discovered with the methylidene bridge needed for cercosporin (see below). Since reexamination of alternate decarboxylation methods [48] led to no success, a decarbonylation strategy was explored [49]. Formation of the requisite dialdehyde was best accomplished by overreduction using DIB AL and... 

Scheme 150).225 227 The pyran products predominate when the ratio of triphenylphosphine to palladium catalyst exceeds two whereas the linear oligomers are the major products when this ratio is close to unity. The suggested227 mechanism (Scheme 151) includes a step of insertion of C=0 into a C—Pd palladium-catalyzed reactions leading to the formation of pyranones (see Scheme 152)228 and piperidones (see Scheme 139 in Section V,A,2).211 It is useful to note that the 2,5-divinyltetrahydropyran derivative can be transformed catalytically by ruthenium trichloride into synthetically useful 3,4-dihydro-2//-pyran derivatives (Scheme 153).229... 

The main path of the palladium-catalyzed reaction of butadiene is the dimerization. However, the trimerization to form /j-1, 3,6,10-dodeca-tetraene takes place with certain palladium complexes in the absence of a phosphine ligand. Medema and van Helden observed, while studying the insertion reaction of butadiene to 7r-allylpalladium chloride and acetate (32, 37), that the reaction of butadiene in benzene solution at 50°C using 7r-allylpalladium acetate as a catalyst yielded w-1,3,6,10-dodecatetraene (27) with a selectivity of 79% at a conversion of 30% based on butadiene in 22 hours. 

As mentioned above nonconjugated dienes give stable complexes where the two double bonds can form a chelate complex. A common pathway in palladium-catalyzed oxidation of nonconjugated dienes is that, after a first nucleophilic addition to one of the double bonds, the second double bond inserts into the palladium-carbon bond. The new (cr-alkyl)palladium complex produced can then undergo a /(-elimination or an oxidative cleavage reaction (Scheme 2). An early example of this type of reaction, although not catalytic, was reported by Tsuji and Takahashi (equation 2)12. 

In relation to palladium enolates, Yamamoto and co-workers reported palladium-catalyzed addition of malononi-trile derivatives to imines or aldehydes (Equation (110)).466,466a Oxidative addition of the C-H bond of the malononitrile to Pd(0) followed by insertion of an electrophile is proposed. 

The 2,3-substituted indols are formed via a palladium-catalyzed coupling reaction of aryl halide, o-alkenylphenyl isocyanide, and amine (Equation (122)).481 Oxidative addition of an aryl halide, insertion of both the isonitrile and alkene moieties of o-alkenylphenyl isocyanide, and 1,3-hydrogen migration may form a 7r-allylpalladium species, which is then attacked by an amine to afford an indol. 

A palladium(0)-phosphine complex also catalyzes insertion of phenylacetylene into the Ge-Ge bond of a benzo-digermacyclobutene (Equation (57)).138 Reaction of a cyclotetragermane with alkynes was also reported.139... 

A unique system for catalytic silaboration of allenes, in which a catalytic amount of organic halide is used as a crucial additive, has been reported (Equation (86)).232 In the presence of Pd2(dba)3 (5 mol%) with 3-iodo-2-methyl-2-cyclohexen-l-one (10mol%), reactions of terminal allenes with a silylborane afford /3-silylallylboranes in good yields with excellent regioselectivity. It is worth noting that the addition takes place at the terminal C=C bond in contrast to the above-mentioned palladium-catalyzed silaboration. The alkenyl iodide can be replaced with iodine or trimethylsilyl iodide. The key reaction intermediate seems to be silylpalladium(n) iodide, which promotes the insertion of allenes with Si-C bond formation at the central -carbon. 

Carbon monoxide rapidly inserts into the carbon—zirconium bond of alkyl- and alkenyl-zirconocene chlorides at low temperature with retention of configuration at carbon to give acylzirconocene chlorides 17 (Scheme 3.5). Acylzirconocene chlorides have found utility in synthesis, as described elsewhere in this volume [17]. Lewis acid catalyzed additions to enones, aldehydes, and imines, yielding a-keto allylic alcohols, a-hydroxy ketones, and a-amino ketones, respectively [18], and palladium-catalyzed addition to alkyl/aryl halides and a,[5-ynones [19] are examples. The acyl complex 18 formed by the insertion of carbon monoxide into dialkyl, alkylaryl, or diaryl zirconocenes may rearrange to a r 2-ketone complex 19 either thermally (particularly when R1 = R2 = Ph) or on addition of a Lewis acid [5,20,21]. The rearrangement proceeds through the less stable... 

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