Dienes palladium catalysis

Allyl sulphones can be converted to dienes by alkylation and elimination of sulphinic acid under basic conditions (equation 64)105. Several vitamin A related polyenes have been synthesized following this two-step protocol (Table 10)106. The poor leaving-group ability of the arylsulphonyl group requires treatment with strong base for elimination. However, elimination of the allylsulphonyl group takes place readily under palladium catalysis (equation 65)107. Vinyl sulphones can be converted to dienes via Michael addition, alkylation with allyl halides and elimination of sulphinic acid sequence (equation 66)108. 

Bromoalkynes also couple with vinylstannanes readily to result in enynes. Synthesis of protected enynals via cross-coupling of vinylstannanes with 1-bromoalkynes in the presence of a catalytic amount of Pd(II) has been reported (equation 143)252. Hiyama and coworkers extended the Stille methodology for sequential three-component coupling of trimethylstannyl(trimethylsilyl)acetylene with a vinyl iodide in the first step and cross-coupling of the intermediate trimethylsilylethyne with another alkenyl iodide in the presence of tris(diethylamino)sulphonium trimethyldifluorosilicate in the second step to generate a dienyne (equation 144)253. Both steps occur under palladium catalysis, in one-pot, to result in stereodefined l,5-dien-3-ynes. 

Trost reported the synthesis of 1,4-dienes with ruthenium catalysis through regioselective carbometallation of alkynes with alkenes.51 Di- and trisubstituted olefins can also be obtained with arylboronic acids through an intermolecular process under rhodium,30 52 55 nickel,56 and palladium catalysis.57 Recently, Larock has reported an efficient palladium-catalyzed route for the preparation of tetrasubstituted olefins.58,59... 

The rearrangement of polyfluoroalkyl-substitutcd alkynes 7 to 1 if,377-dienes 8 can be achieved with palladium catalysis.59... 

A-170a and Z-170a, which under palladium catalysis afforded the expected bicycle 169a. The two-step synthesis of compound 169a from diene 164d is depicted in Scheme 59. 

Synthetic methods for the preparation of dienes and enynes abound, yet the use of alkenyl iodonium salts offers distinct advantages. Their coupling reactions with electron-deficient alkenes and alkenyl- or alkynylstannanes constitute a valuable extension to the previously existing methodology, because of mild conditions, ease of operation, high stereoselectivity and good yields. The simplest reaction of this category is with unsaturated carbonyl compounds and requires palladium catalysis. 

Hi. Carbon-silicon bonds. Following the earlier reports mentioning the palladium-catalysed addition of organosilylstannanes to alkynes or isonitriles , Mori and coworkers realized tandem transmetallation-cyclization reactions with bifunctional halogeno triflates and Bu3SnSiMe3 18. The reactivity of 18 under palladium catalysis was used for the silylstannylation of alkenes or the synthesis of allylic silanes via a three-component (aryl iodide - - diene - - 18) coupling reaction. Recently, a similar... 

In 2002, Rawal developed a tandem reaction via multifunction palladium catalysis combining haloallylation and the Wacker-Tsuji oxidation.53 For example, internal alkyne 68 first underwent a bromoallylation to give a 1,4-diene, which was subsequently oxidized to the methyl ketone 69 without addition of the palladium catalyst. 

Starting from dimedone, 3-allyl-substituted cyclohexa-l,4-diene-2,4-diyl bisnonafluo-robutanesulfonates have been prepared in four efficient steps. These 1,5-hexadienes under palladium catalysis first undergo intramolecular carbopalladation followed by dehydropalladation to yield a 8-methylenebicyclo[4.2.0]octa-l,4-dien derivative, which subsequently couples intermolecularly with added tert-butyl acrylate. In the presence of... 

Another potentially powerfnl sequence arises by combining one or two intramolecular Heck-type couplings with an intra- or intermolecular Diels-Alder addition (for early examples of inter-intermolecular one-pot domino Heck-Diels-Alder reactions see Refs. [49] and [50]). An all-intramolecular version of such a sequence has been shown to proceed reasonably smoothly for terminally alkoxycarbonyl-substituted 2-bromotrideca-l,ll-dien-6-ynes under palladium catalysis at 130 °C. At 80 °C, the sequential reaction stops after the two consecutive Heck-type cyclizations and subsequent /3-hydride elimination to give a 1,3,6-triene apparently only the ( )-isomer undergoes the intramolecular Diels-Alder reaction, as the (Z)-l,3,6-triene is observed accompanying the tetracyclic system obtained at 130 °C (Scheme 36). 

Simple 1,3-dienes such as 1,3-butadiene, isoprene, and related compounds undergo efficient metal-catalyzed oligomerization. Under palladium catalysis, diene dimerization is the most common oligomerization reaction observed. Four modes of dimerization have been reported (Scheme 1) (i) [2 + 2] cycloaddition to afford 1,2-divinylcyclobutane (1) (ii) [4 -I- 2] cycloaddition to afford 4-vinylcyclohexene (2) (iii) [4 + 4] cycloaddition to afford 1,4-cyclooctadiene (3) and (iv) linear dimerization to afford 1,3,7-octatriene (4). 

While the intermolecular reactions of butadiene and related methyl or simple alkyl-substituted dienes have been investigated extensively, relatively few examples of the Pd-catalyzed linear dimerization of higher dienes have been reported. Brun and co-work-ers in an isolated paper reported that, under palladium catalysis, reaction of methyl 2,4-pentadienoate (Scheme 9, 28) affords the linear dimer 29 in high yield (95%). Two aspects of this reaction are of particular interest, (i) The dimerization yields essentially only the tail-to-tail dimer 29, not the head-to-tail or head-to-head isomers (30 or 31, respectively). This is in contrast to the behavior of alkyl-substituted dienes under similar conditions vide infra), (ii) Although no details are given, the authors imply that 29 is... 

With ruthenium catalysts the same products are formed as in palladium catalysis, i.e. the Cg-6-lactone and traces of esters (compare Equation 6). Ruthenium(II)-hydrido-phosphine complexes such as RuH(OAc)-(PPh3)3, RuH2(PPh3)4, RuH(OAc)(CO)(PPh3)2 or RuH (C0)(PPh3)3 can be used as catalyst precursors. When triisopropyl phosphine is added as ligand yields up to 7 5l> are obtained. Of course, the yields are rather low, however, this is the first proof that both rhodium and ruthenium are active catalyst metals in diene/C02 chemistry. 

Asymmetrically induced Heck reactions can also be performed with substrates containing two enantiotopic leaving groups. Starting from dimedone, novel cyclohexa-l,4-diene-l,5-diol bis(nonafluorobutanesulfonates) such as 309 have been prepared and cycUzed under palladium catalysis to cleanly give bicy-clo[4.2.0]octadienes 370 and bicyclo[4.2.0]octenones, respectively, by an unprecedented 4-exo-trig process (Scheme 8.77, cf. Scheme 8.66). In the presence of a chiral phosphine ligand, the products could be obtained with modest enantiomeric excesses (up to 52% ee) [239]. 

Cyclic secondary amines are also produced by the ring expansion of O-sulphonyloximes via a Beckmann rearrangement/ the cyclization of a,aliphatic diamines by a ruthenium catalyst/ the palladium-promoted ring closure of amino-alkenes/ and the sulphonamidomercuration of 1,4- and 1,5-dienes. The latter two reactions form part of a wealth of new literature on the amination of olefins and acetylenes via aminomercuration " and via palladium catalysis. ... 

Previous work in our laboratory demonstrated that -vinyl iodides could undergo oxidative addition to Pd. Thus, utilization of the palladium catalysis cycle (with RpCF=CF- in place of Ar-) would provide a useful, stereospecific route to E-dienes.Thus, we found that Ae following dienes could be stereospecifically prepared via this approach (8). 

SCHEME 7.43 Improvement of diene cycloisomerization with hydrosilane additives under palladium catalysis. 

The utility of the platinum-catalyzed enyne cycloisomerization for the formal synthesis of Rosephilin, which is a member of prodiginine family of alkaloids, was reported by Trost and Doherty (Scheme 7.44) [94]. The critical step in the synthesis was the conversion of enyne 221 to bicyclic diene 222 by platinum-catalyzed enyne cycloisomerization. While palladium catalysis was found to be ineffective, the desired cyclopentene 222 was obtained when 221 was treated with the platinum-based catalytic system developed by Murai. Diene 222 was converted to tricyclic pyrrole intermediate 223 in an 11-step sequence. Since 223 had been converted to roseophilin 224, the entire procedure represented a formal synthesis of the alkaloid. 

The usual cyclopropanation reagent, diazomethane and diazoacetates, react smoothly with alkenes in the presence of palladium-catalyst to form cyclopropanes. However, it should be noted that rhodium complexes serve in most cases as superior catalyst. Cyclopropanes can be formed from alkenes (dienes) and nucleophiles using oxidative palladium catalysis (Scheme 5-175). In this case, copper(II) salts regenerate the palladium(II) complexes. The vinyl cyclopropanes produced undergo subsequent vinylcyclopropane-cyclopentane rearrangement to form bicycles. ... 

As another example leading to novel conformationally restricted peptidomimetics, a Pd-catalysed enyne cycloisomerization was described as a route to macrocyclic diene structures (119, Figure 11.13, site of ring closure and palladium species indicated). Subsequent [4+2] cycloadditions with dienophiles then gave the target molecules. An interesting application of the use of palladium catalysis in macrocyclization was reported by Barnickel and... 

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. ... 

Terminal alkynes react with propargylic carbonates at room temperature to afford the alka-l, 2-dien-4-yne 14 (allenylalkyne) in good yield with catalysis by Pd(0) and Cul[5], The reaction can be explained by the transmetallation of the (7-allenylpailadium methoxide 4 with copper acetylides to form the allenyKalk-ynyl)palladium 13, which undergoes reductive elimination to form the allenyl alkyne 14. In addition to propargylic carbonates, propargylic chlorides and acetates (in the presence of ZnCb) also react with terminal alkynes to afford allenylalkynes[6], Allenylalkynes are prepared by the reaction of the alkynyl-oxiranes 15 with zinc acetylides[7]. 

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