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Palladium acetate 3 + 2 cycloaddition reactions

The parent TMM precursor (1), now commercially available, has played a pivotal role in the execution of many synthetic plans directed at natural and unnatural targets. Reaction of (1) with 2-(methoxycarbonyl)cyclohexenone (14, R=C02Me) in the presence of palladium acetate and triethyl phosphite produced the adduct (15) in near quantitative yield. This cycloadduct is a critical intermediate in the total synthesis of a hydroxykempenone (16), a component of the defensive substances secreted by termites (Scheme 2.5) [12]. In accord with a previous observation by Trost that unactivated 2-cyclohexenone reacts poorly with TMM-Pd [13], the substrate (14, R=Me) was essentially inert in the cycloaddition. [Pg.61]

Mercury(II) chloride, 175 Palladium(II) acetate, 232 Titanium(IV) chloride, 304 By [3 + 2] cycloaddition reactions 3-Acetoxy-2-trimethylsilylmethyl-l-propene, 3... [Pg.395]

The presence of five-membered rings such as cyclopentanes, cyclopentenes, and dihydrofurans in a wide range of target molecules has led to a variety of methods for their preparation. One of the most successful of these is the use of trimethylenemethane [3 + 2] cycloaddition, catalysed by pal-ladium(O) complexes. The trimethylenemethane unit in these reactions is derived from 2-[ (trimethylsilyl)methyl]-2-propen- 1-yl acetate which is at the same time an allyl silane and an allylic acetate. This makes it a weak nucleophile and an electrophile in the presence of palladium(0). Formation of the palladium 7t-allyl complex is followed by removal of the trimethylsilyl group by nucleophilic attack of the resulting acetate ion, thus producing a zwitterionic palladium complex that can undergo cycloaddition reactions. [Pg.1334]

As an approach to the synthesis of piperidines with stereocontrol, multiple functionality, and flexibility, the authors employed a [3+3] cycloaddition reaction of a silylpropenyl acetate with aziridines in the presence of a palladium catalyst. The key intermediate is a palladium-trimethylenemethane (Pd-TMM) complex <03JOC4286>. Optically active aziridines gave enantiomerically pure piperidines. [Pg.334]

In nickel-catalyzed reactions, the cyclopentane with the electron-withdrawing group in the 3-position (relative to the exo-methylene group) is formed almost exclusively. This is in contrast to the palladium-catalyzed, formal [3-1-2] cycloaddition employing 2-(trimethylsilylme-thyl)prop-3-enyl acetate as precursor, which presumably follows a mechanistically different, ionic pathway. In palladium-catalyzed MCP reactions of that type, the observed selectivity is markedly dependent on the specific reactants. [Pg.2224]

Palladium-based catalysts also bring about cyclopropanations in high-yield. With palladium acetate/CHjNj, styrene , unactivated terminal olefins strained olefins , 1,3-dienesan enamine , as well as a,3-unsaturated carbonyl compounds have been cyclopropanated (Table 1). Contrary to an earlier report, the reaction also works well with cyclohexene if the conditions are chosen appropriately it seems that the notniyst is rapidly deactivated in the presence of this olefin >. Trisubstituted a,p-unsaturated carbonyl compounds were found to be unreactive, and the same is true for the double bonds in diethyl fumarate, maleic anhydride, coumarin and 1,3-dimethyluracil. Whereas the latter two were totally unreactive, [3-1-2] cycloaddition of diazomethane gave pyrazolines in the former two cases. The last entry of Table 1 shows that an allyl alcohol function can still be cyclopropanated, but methylene insertion into the O—H bond is a competing process. [Pg.79]

These cycloadditions are more sensitive to the quality of the catalyst, the major side reaction being protodesilylation of the allylsilane subunit. Since this can not be measured readily either in the case of the tetrakis(triphenylphosphane)palladium(0) or the palladium acetate/triisopropyl phosphite methods, an improved method for generating the palladium(O) species has been developed22. This involves in situ preparation of tetrakis(triisopropyl phos-phite)palladium(O) by direct reduction of palladium acetate with butyl lithium. This method is illustrated by the addition of the methyl-substituted TMM-Pd complex to eyelopentenone. [Pg.814]

In contrast to cyclohexenone, the unsaturated sulfoxide proved to be an excellent substrate for the [3 + 2] cycloaddition. The reaction was carried out in refluxing toluene using a catalyst derived from palladium acetate and triisopropyl phosphite, the latter acting both as a reducing agent and as a ligand. [Pg.838]

D.iii. Trimethylenemethane Equivalents. Palladium catalysts can be used to convert trimethylsilyl acetate 390 to a trimethylene methane (TMM, 391) equivalent. Reaction with alkenes via [3+2]-cycloaddition (sec. 11.11) generates cyclopentanes (this process constitutes a quinane annulation reaction).229 in this reaction, the trimethylsilyl unit is a carbanion equivalent and acetate is a carbocation equivalent. In one example, Trost reacted 390 and 392 with palladium acetate and triisopropyl phosphite [P(Oi-Pr)3] to generate 393 in... [Pg.1118]

Activated acetylenic compounds, for example esters RC=CC02R" undergo cycloadditions to adenosine derivatives to yield two possible products (3, 4), depending on the conditions or reaction. The derivatives of 2-alkynoic acids undergo a regiospecific and stereospecific hydroacetoxylation reaction, catalysed by palladium acetate, as shown in reaction 2. ... [Pg.198]

Stork s strategy towards racemic morphine comprises a Diels-Alder cycloaddition reaction of a benzofuran to establish the B- and C-ring of morphine as the key step [53]. The reaction sequence started with the ketahzation of iodoisovaniUin 97 (Scheme 15). Subsequently, the phenol was reacted with methyl propiolate to afford 98 as precursor for the installation of the benzofuran moiety via a palladium-catalyzed Heck cyclization (99). Next, the key intermediate was prepared for the Diels-Alder reaction. Hydrolysis of the acetal under acidic conditions and Wittig homologation afforded aldehyde 100, which was converted to diene 101 via hydrozirconation of acetylene 105 employing the Schwartz reagent and subsequent reaction with aldehyde 100 followed by sUylation of the secondary alcohol. [Pg.54]

The palladium-catalyzed [3+2] cycloaddition reaction between enantiomerically pure a,P-unsaturated sulfoxides and trimethylenemethane (266), using the methodology developed by Trost [198], has been reported [199]. Thus, reaction of the sulfoxide (31), 2-acetoxymethyl-3-allyltrimethylsilane (2eq), palladium acetate (5mol%), and triisopropylphosphite (20 eq) in THF under reflux gave the major cycloadduct (267) in 80% yield and 80% de (Scheme 5.87). Moderate to good levels of asymmetric induction were observed for various a,P unsaturated sulfoxides. [Pg.213]

Total syntheses of diterpenoid hydrokempenones have been accomplished by Paquette et al.,f using the Pd-catalyzed [3 + 2] cycloaddition methodology. One example is outlined on Scheme 43 and describes the synthesis of an isomeric compound 208 of 3/3-hydroxy-7/3-kemp-8(9)-en-6-one, a defense secretion agent of the neotropical species Nasutitermes octopilis. 3-AUcoxy-2-cyclohexenone 204 was efficiently functionalized and transformed to bicylic adduct 205 via a Robinson annulation reaction. Reduction of the double bond followed by condensation of dimethyl carbonate and oxidation gave the keto ester 206, which was treated with [2-(acetoxymethyl)-3-allyl]trimethylsilane, palladium acetate, and triisopropyl phosphite in refluxing tetrahydrofuran to afford a 98% yield of 207. Substituted methylenecyclopentane 207 was then functionalized by stereoselective reduction and protections, and final closure was done under basic conditions after an ozonolysis step. A modified Barton-McCombie reaction produced the desired tetracyclic adduct 208. [Pg.431]


See other pages where Palladium acetate 3 + 2 cycloaddition reactions is mentioned: [Pg.183]    [Pg.81]    [Pg.22]    [Pg.24]    [Pg.183]    [Pg.95]    [Pg.81]    [Pg.599]    [Pg.122]    [Pg.41]    [Pg.130]    [Pg.283]    [Pg.243]    [Pg.2247]    [Pg.144]    [Pg.840]    [Pg.841]    [Pg.46]    [Pg.46]    [Pg.139]    [Pg.283]    [Pg.317]    [Pg.143]    [Pg.122]    [Pg.430]    [Pg.62]   
See also in sourсe #XX -- [ Pg.299 ]

See also in sourсe #XX -- [ Pg.299 ]

See also in sourсe #XX -- [ Pg.5 , Pg.299 ]




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