Alkenylations silver carbonate

Optimum yields of (3-vinyl-y-butyrolactols from the Pd(II) promoted reaction of vinyl triflates with Z-but-2-en-l,4-diol (Scheme 6.33) are attained when tetra-n-butylammonium chloride is added (47]. The lactol is conveniently oxidized to the lactone with celite-supported silver carbonate. The corresponding arylbutyrolactols are obtained in high yield (70-80%) from an analogous reaction of iodoarenes with the enediol. The yields of 2-alkenyl-2,5-dihydrofurans, resulting from the Pd(0) catalysed reaction of cyclic alkynylcarbonates with acrylic esters via tandem C-C and C-0 bond forming reactions, are enhanced by the presence of tetra-n-butyl-ammonium fluoride (e.g. Scheme 6.33) (48]. 

Alkenylations can also be carried out the optimum conditions for 2-bromopropene with palladium acetate include the use of triphenylarsine with silver carbonate and triethylamine, but the advantages over more amenable conditions, using triphenylphosphine with potassium or cesium carbonate, are marginal. ... 

Fulvenes are obtained by the Pd-catalyzed reaction of alkenyl iodides with two alkynes [7,8], The pentasubstituted fulvene 23 was obtained in good yield from two molecules of 3-hexyne and the alkenyl iodide 22 in the presence of an equimolar amount of silver carbonate without phosphine [9], In this reaction,... 

Terminal alkenes can be used in a palladium-catalyzed alkenylation reaction of pyridine, pyrazine, quinoxaline, and pyridazine N-oxides 109 as reported by Chang (Scheme 53) (2008JA9254). This approach delivers regioselective C2-alkenylation products 110 and requires silver carbonate in a superstoichiometric amount as external oxidant. 

The conversion of acetylenes into olefinic esters by use of addition reactions has been illustrated by the following two examples, (i) 1-Alkenyl boranes, which are readily prepared by the hydroboration of alkynes, are converted into a,fi-unsaturated carboxylic esters in good yield by reaction with carbon monoxide in the presence of palladium chloride and sodium acetate in methanol the process is carried out at atmospheric pressure and occurs with retention of configuration with respect to the alkenyl borane. (ii) Carboxylic acids add to acetylenes in the presence of silver carbonate to provide a novel synthesis of enol esters, which are formed in an 8 2 mixture of isomers. ... 

A unique rhodium-catalyzed oxidative alkenylation of diarylmethanols having a 2-(2-pyridyl) moiety with alkenes using silver carbonate as oxidant was reported (Scheme 4.99) [98]. The diarylmethanols also underwent a rhodium-catalyzed aldehyde-imine exchange reaction [99]. 

Examples of silver(l) alkyl and alkenyl (including aryl) complexes have been known from as early as 1941 6-9 however, the number of examples is fairly limited with respect to that of the heavier congeners, copper(l) and gold(l). Such a phenomenon can readily be attributed to the relatively low stability of this class of complexes, both photochemically and thermally. Simple homoleptic alkyl and alkenyl complexes of silver(i) are known to be very unstable under ambient temperature and light, and successful isolation of this class is fairly limited and mainly confined to those involving perfluoroorganics.10 The structures and the metal-carbon bond-dissociation energies for... 

Scheme 82 shows the intramolecular version of the reaction using an alkenyl iodide in the presence of the same Pd system containing silver phosphate (194,195). The reaction can also be used for the asymmetric synthesis of quaternary carbon centers. 

The enormous potential of the intramolecular Heck reactions has been demonstrated impressively in elegant syntheses of even the most complicated natural product skeletons. The intramolecular Heck reaction on the achiral iodoalkenes 354 and the corresponding alkenyl triflates 357 with their pairs of enantiotopic double bonds in the cyclohexa-1,4-diene moieties, applying catalysts with chiral ligands, gave tetrahydronaphthalenes 359 or hydrindanes from precursors such as 354, 357 or corresponding precursors with one less carbon in the tether [204f], with excellent enantioselectivities. Complementary to the asymmetrically induced inter-molecular arylation with triflates (Scheme 8.72), reasonable asymmetric inductions in intramolecular reactions were also achieved with iodides on the addition of silver salts to promote the formation of cationic intermediates such as 356 (Scheme 8.73)... 

Triazole iV-oxides could be site-selectively C5-alkenylated under oxidative conditions using silver(I) carbonate as an oxidant and pivalic acid as an additive (eq 7). ... 

A cationic Rh-catalyst was employed in the presence of silver(I) carbonate to alkenylate heteroarylphosphine oxides. Thiophene derivatives underwent alkenylaton in modest to good yields (59-72%) using ethyl and terf-butyl acrylates (eq 38). 

Silver(I) carbonate functioned as an co-oxidant with TEMPO. Tricyclohexylphosphine was employed to suppress homocoupling between heteroarenes. Substituted thiophenes, furans, and indoles could be selectively olefinated (C5-alkenylation for thiophenes and furans, C3-alkenylation for indoles, E/Z <99 1). Unsubstituted thiophenes produced poor yields (24%) however, formyl, acetyl, and ketyl substituents were well tolerated. For electron-deficient substrates, tricyclohexylphosphine was reduced to 10 mol % to achieve good conversions. A variety of ketones could be employed using 2-methyl thiophene as a coupling partner. 

Most of the above oxidative alkenylations take place with 2-5 mol% of a Ru (11) species and excess of silver salt, usually 20 mol%, and 1 equiv of Cu(ll) unless the reaction can be performed in air. As [RuCl2(p-cymene)]2 leads to partial formation of Ru(OAc)2(p-cymene) with Cu(0Ac)2.H20 [160], AgSbFg by abstracting the chlorides is expected to increase the formation of Ru (OAc)2(p-cymene). The Ru-OAc bond of the latter dissociates easily [49, 91] to allow the coordination of the heterocycle Directing Group (D=G) to the Ru (II) centre (Scheme 16). The interaction of the Ru(II) site with the ortho carbon atom (A) is expected to favour the deprotonation of its C-H bond by the external... 

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