Allenes palladium catalysis

Butylallene, which fails to react with (PhSe)2 under palladium catalysis, undergoes the diselenide addition upon photo-irradiation (Equation (80)).215 Using the (PhS)2/(PhSe)2 binary system, introduction of two different chalcogen elements into allenic C=C bond is also viable (Equation (81)). 

Aside from alkoxycarbonylations, hydroxycarbonylations in the presence of water to yield allenic carboxylic acids [15] (93, Y = OH) and aminocarbonylations in the presence of amines to give the analogous amides [139] (93, Y = NRR ) have also been carried out, respectively (Scheme 7.13). These products of structure 102 can also be obtained if using the propargylamines 101 with R1 = Ph or R3 Z H as starting materials (Scheme 7.15) [140]. Additionally, hydroxycarbonylations, also termed carboxyla-tions, are successful without palladium catalysis by reaction of propargyl halides and carbon monoxide in the presence of nickel(II) cyanide under phase-transfer conditions [141, 142]. 

A few synthetic applications of palladium catalysis appeared this year. The palladium-catalyzed cyclization of amino allenes 58 occurs with coupling of aryl iodides or vinyl triflates at the 3-position <990L717, 99SL324>. The cyclization can also proceed by the exo-trig pathway, but under suitable reaction conditions the piperidine 59 is prepared selectively. The intramolecular cyclization of amines onto N-allylbenzotriazoles similarly affords piperidines <99JOC6066>. 

Under palladium catalysis, the < -iodoallenylbenzene 146 first undergoes an intermolecular carbopalladation of the double bond in the added norbornene 116, and only then follows an intramolecular carbopalladation of the allene moiety in 146 ensuing /3-hydride elimination finally provides the tricyclic compound 147 (Scheme 37)7 ... 

It is reported that the palladium-catalysed intramolecular aromatization of 1,1 -dichloro-9/T-fluoren-9-yIidene (15) may lead to the formation of fullerene fragments.89 The amiulation reaction, under palladium catalysis, between iodoanflines and ketones may yield indole derivatives.90 There have also been studies of the palladium-catalysed carbonylation of o-iodophenols with allenes which may lead to l-benzopyran-4-one derivatives,91 of the intramolecular coupling of phenols with aryl halides,92 and of the intramolecular Heck aiylation of cyclic enamides.93... 

A new type of triaryl phosphine-functionalized imidazolium salt containing cations such as (6) has been prepared. Palladium complexes of (6) generated in situ have been used successfully in Heck-type reactions of aryl halides with acrylates and of 4-bromotoluene with styrene derivatives.34 The first Heck-type reaction of aryl halides with allenes has been reported. 1,3-Double arylations were observed with 3-substituted-l,2-allenyl sulfones, while 1-monoarylation was favoured with 3,3-disubstituted-l,2-allenyl sulfones.35 It has been shown that the a-arylation of methane-sulfonamides (7) may be achieved using palladium catalysis reaction proceeds through the sulfonamide enolates.36 It is also reported that palladium cross-coupling of alkynes with /V - (3 - i odophe n y I an i I i ncs) may lead to the formation of substituted carbazoles.37... 

An interesting reaction between the bis phenyl iodonium triflate of acetylene and the silyl enol ether of acetophenone afforded an allene (PhCOCH=C=C=CHCOPh, 84%) [6], Also, alkynyl iodonium tosylates and carbon monoxide in methanol or ethanol, with palladium catalysis, furnished alkyne carboxylates [53]. 

The formation of (31) was favoured in most reactions tried, presumably due to the directing influence of the hydroxyl group present as the lithium anion. Palladium catalysis finds yet another fruitful application in the conversion of acetylenic carbonates to allenic products. The allenylpalladium complexes... 

A new preparative method for allenes has appeared (Scheme 4). Several alk-2-ynyl carbonates (prepared by nucleophilic addition of magnesium and lithium acetylides to ketones or aldehydes followed by quenching with methyl chloroformate) were selectively hydrogenolysed with ammomium formate under palladium catalysis to give allenes in good yields. 

Allenyl ketones presynthesised, or generated in situ by acylation of silyl-allenes, or by palladium(0)-catalysed isomerisation of conjugated or non-conjugated alkynyl ketones, can be cyclised to furans. The ring closure has been effected with silver or palladium catalysis acylation of silylallenes leads to the furan directly. In the presence of water, palladium(II)-catalysed closure of / ,7-alkynyl ketones is believed to proceed via the enol, not the allene. l,2,3-Trienyl-4-ols have also been shown to cyclise to give furans. ... 

While furans have been the main focus of palladium-catalyzed allene cycloisomerization, pyrroles can also be generated via reaction of allenyl-substituted amines. A number of metal catalysts have been reported to mediate the cyclization of these substrates to pyrrolines, however, the use of palladium catalysis can allow the concomitant incorporation of aryl functionality into the 3-position, as shown in Scheme 6.27. At elevated temperatures, oxidation of the pyrroline occurs to afford pyrroles [37]. 

A comparison of reaction conditions has shown that palladium catalysis is particularly effective in achieving complete chiral transfer (eq 3). Propargylic imidates also rearrange when heated in refluxing xylene. The initially formed allene undergoes a series of tautomerizations so that amino 1,3-dienes are the ultimate products (eq 4). These dienes have found use in the Diels-Alder reaction. ... 

With catalysis by tetrakis(triphenylphosphane)palladium(0), the reaction of allenic amides 275 and aryl or vinyl iodides afforded Z-configured iminolactones 277... 

If allenes bear a potential leaving group in the a-position to the cumulene system, they are very attractive substrates for palladium-catalyzed substitutions. Examples are a-allenic acetates and particularly a-allenic phosphates, which react under palladium(O) catalysis with carbanions derived from /3-diesters, /i-keto esters, a-phenylsulfonyl esters and glycine ester derivatives. They lead to /3-functionalized allenes such as 86, 89 and 93 (Eqs. 14.9-14.11) [45 18]. 

Joint catalysis by tin(IV) chloride and zinc chloride induces coupling of the acetal 114 with the alkyne 115 to give the propargyl ether 116. Allyl halides condense with terminal alkynes in DMF in the presence of copper(I) iodide, potassium carbonate and tetrabutylammonium chloride under phase-transfer conditions to afford eneynes, e.g. equation 19. Palladium-catalysed coupling reactions of 1-bromoallenes with terminal acetylenes have been reported for the first time thus acetylene and the allenes 117 (R R = Me or Et) in triethylamine in the presence of tetrakis(triphenylphosphine)palladium and... 

The cycloisomerization of a-allenyl ketones to the corresponding substituted furans was the first example of a gold-catalyzed addition of an oxygen nucleophile to an allene (Scheme 4-86). Traditionally, silver or palladium catalysts were employed for cyclizations of this type advantages of gold catalysis incluiie shorter reaction times, milder conditions, an or lower catalyst loadings. Variable amounts of... 

The reaction of allenic ketones 6.205 with a gold(lll) catalyst proved to give a much faster reaction than with silver catalysts, to give substituted furans, 6.206 and 6.207 (Scheme 6.70). In the products, a second molecule of the substrate adds to the initial product, to give 2,5-disubstituted fiiran. Interestingly, palladium(II) catalysis, also slower than gold catalysis, gives the isomeric series of products 6.208. 

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