Palladium catalysed propargylation

Examples of the formation of sulphur containing heterocycles by similar transformations are quite rare. The palladium catalysed ring closure of S-propargyl-2-iodophenylmercaptane in the presence of formic acid and an amine-base, analogously to phenols and anilines, led to the formation of the partially reduced benzothiophene skeleton, bearing a 3-methylydene function (3.32.),40... 

Terminal arylalkynes can be prepared by oxidation-decarbonylation of 3-arylpropargyl alcohols using manganese dioxide in the presence of alkali. The corresponding arylpiopargyl dcohols are available by palladium-catalysed cross-coupling of aryl halides with commercial propargyl alcohol. The yield of the second step can be improved by the addition of a phase-transfer catalyst (18-crown-6 Scheme 18). ... 

Allene carboxylates have been synthesized from propargylic carbonates using a palladium-catalysed decarboxylation-carbonylation... 

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... 

Reaction of the alkenyl iodide with a lithium organocuprate, or with an organometallic species in a palladium-catalysed coupling, gives the corresponding substituted allylic alcohol (in which the substituents originally present in the propargylic alcohol are trans to each other). This method is applicable to a variety of synthetic problems in which the stereoselective introduction of a trisubstituted carbon-carbon double bond is involved. For example, it formed a key step in a synthesis of juvenile hormone (2.64). 

Dicarbonyl compounds have featured in several approaches to dihydrofurans under a variety of reaction conditions. The palladium-catalysed reaction of propargyl carbonates with ethyl acetoacetate generates 4-methylene-4,5-dihydrofurans (57) in high yield (79-94%) in neutral media but the use of B-diketones leads to... 

Palladium-catalysed carbonylation of an iodoallylic alcohol, stereoselectively formed from the propargylic alcohol 4.57 through organoaluminium chemistry, was employed to form the base sensitive butenolide moiety of parviflorin 4.62 in a two-directional synthesis (Scheme After oxidative removal of the protecting... 

A novel catalyst system has been developed for the stereoselective palladium-catalysed exo-cyclization of allenes (83) upon addition of organic halides R I or their equivalents, such as propargylic carbonates, to produce (84). ... 

A synthesis of 2 -0-methyluridine has been carried out by a procedure in which the 3, 5 -0-TIPDS derivative of uridine was protected at N-3 by the p-methoxybenzyl group,208 and the "wobble position" nucleoside 2 -0-methyl-5-(methoxycarboxylmethyl)uridine has also been prepared by similar means.209 The 2 -0-allyl derivative (141) of uridine is accessible by a palladium-catalysed decarboxylation of (142), and a similar reaction is possible on an adenosine derivative.210 2 -0-Propargyl uridine can be prepared via the 2, 3 -0-dibutylstannylene derivative the triple bond of this derivative could then be converted into an unusual carboranyl group, the resultant structure being of potential use in the neutron capture therapy of cancer.211 A conference report has discussed the use of 2-(methylthio)-phenylthiomethyl (MPTM) ethers for protection of the 2 -hydroxyl group in oligoribonucleotide synthesis.212... 

Tabuchi,T. Inanaga, J. Yamaguchi, M. Palladium-catalysed Reduction of Propargylic Acetates with Sml2 A Mild and Convenient Method for the Preparation of Allenes . Tetrahedron Lett. 1986,27, 5237-5240. 

Palladium-catalysed cyclisation of olefinic propargylic diethyl phosphate (73) afforded bicyclic trienes (74) (Scheme 24). ... 

Air-stable palladium(O) catalyst, [(Cy3P)2Pd(H)(H20)]BF4, catalyses carbonylation of propargylic alcohols to generate dienoic acids and esters (equation 167)286. Since propar-gyl alcohols are obtained from carbonyl compounds by acetyhde addition reactions, this sequence constitutes a three-carbon homologation. a-Allenic alcohols are converted to tt-vinylacrylic acids under similar conditions (equation 168)287. 

Silyl propargyl alcohols, XC=CSiMe2R [X=RiCH(OH)CHR2CH(SPh)], can undergo palladium(II)-catalysed cyclization to give 2,3-dihydrofurans, or alkyne... 

The transition metal catalysed formation of five membered heterocycles through the insertion of a triple bond has also been explored. o-Halophenyl-alkynylamines, propargylamines and propargyl-ethers have been subjected to ring closure reactions. These processes, however also require the presence of a second, anionic reagent, which converts the palladium complex formed in the insertion step to the product. 

Palladium(0)-catalysed selective allene formation by hydrogenolysis is a convenient synthetic route to allenes from propargylic alcohols. The method offers a new and efficient preparative method for allenes from easily available propargylic alcohols after converting them to formates or carbonates. The best catalyst for smooth hydrogenolysis is prepared by mixing Pd(OAc)2 or Pd(acac)2 with -Bu3P in a ratio... 

Z)-Phenol-substituted alkenes (67) can be produced by the palladium(0)-catalysed reaction of propargylic oxiranes (66) with phenols. This regio- and stereo-selective (g) addition is believed to occur via the formation of 7t-propargyl- and Tr-allylpalladium complexes. The phenoxy-substituted enones were obtained as by-products and their proportion depended on the reaction conditions.75... 

Palladium or nickel catalysed cross-coupling involving alkyl, allyl, propargyl, and benzyl groups 2.3.1 Palladium or nickel catalysed alkylation... 

Esters 106 (R = Me, Et or Pr = Et, Pr, r-Bu or PhCHi) of aliphatic carboxylic acids react with lithium acetylides 107 (R = H, C5 Hi i or Ph) in the presence of boron trifluoride etherate in THE to give acetylenic ketones 108 (equation 18). Palladium-[tetrakis(triphenylphosphine)]-copper(I) iodide catalyses the oxidative addition-decarboxylation of propargyl methyl carbonates, e.g. 109, with terminal alkynes to yield 1,2-dien-4-ynes (allenylacetylenes) 110. The regiochemistry of the palladium-catalyzed addition of phenylacetylene to the allenic ester 111 depends on the nature of the catalyst used palladium(III) acetate-triphenylphosphine yields a 81 19 mixture of adducts 112 and 113, while in the presence of tetrakis(carbomethoxy)palladacyclopentadiene-tris(2,4,6-trimethoxyphenyl)phosphine the ratio is reversed to 9 91 k... 

While the a-allylation of enolates occurs with high ee using palladium catalysts (see Section 10.2) there have been few reports on the enantioselective metal-catalysed enolate alkylation. The best results to date have been achieved by Doyle and lacobsen using the chromium(salen) complex (12.42) in the alkylation of cyclic tin enolates with a range of alkyl halides, including propargyl and benzylic hahdes... 

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