Allylation of alkynes

Some of these coupling reactions can be made catalytic if hydrogen is eliminated and combines with the anion, thus leaving the nickel complex in the zero-valent state. Allylation of alkynes or of strained olefins with allylic acetates and nickel complexes with phosphites has been achieved (example 38, Table III). 

Intramolecular allylation of alkynes with allylsilanes can be catalyzed by electrophilic transition metal halides and complexes (e.g. Pt(ll), Pd(ll), Ru(ll), Au(m), and Ag(l)).214,2143 A Pd(ll)-catalyzed system using a reoxidant is effective in oxidative intramolecular allylation of 1,3-dienes (Equation (56)).215,2153 These allylations are initiated by coordination of the electrophilic metals to alkynes and 1,3-dienes. 

The allylation of terminals alkynes catalyzed by Cu salts proceeds smoothly under solid/liquid PTC conditions [178]. More recently, it was shown that the allylation of alkynes can be effectively carried out under classical liquid/liquid PTC conditions in the presence of CuCl and quaternary ammonium salt [179]. 

Intramolecular allylation of alkynes with allylsilanes is catalyzed by a variety of electrophilic transition metal halides and complexes (e.g. Pt(II), Pd(II), Ru(II), Au(III), and Ag(I)) (Scheme 10.196) [518]. Unlike the EtAlCl2- or HfCL,-catalyzed reaction, alkyriylaled allylsilanes are cyclized in an exo mode by these catalysts. The proposed reaction mechanism involves nucleophihc addition of an allylsilane to a metal-coordinated alkyne. 

Recent studies on the allylation of alkynes with bis (7r-allyl) nickel have revealed that the Ni(0) generated in this process causes the trimeri-zation and, more importantly, the reductive dimerization of a portion of the alkyne (8). A deuterolytic work-up led to the terminally di-deuter-ated diene (5), supporting the presence of a nickelole precursor (4) (Scheme 1). The further interaction of 4 with 1, either in a Diels-Alder fashion (6) or by alkyne insertion in a C-Ni bond (7), could lead to the cyclic trimer 8 after extrusion of Ni(0), thereby accounting for the trimerizing action of Ni(0) on alkynes. This detection of dimer 5 then provided impetus for the synthesis of the unknown nickelole system to learn if its properties would accord with this proposed reaction scheme. Therefore, E,E-l,4-dilithio-l,2,3,4-tetraphenyl-l,3-butadiene (9) was treated with bis (triphenylphosphine) nickel (II) chloride or l,2-bis(di-phenylphosphino ethane)nickel(II) chloride to form the nickelole 10 (9) (Scheme 2). The nickelole reacted with dimethyl acetylenedicarboxylate to yield 11 and with CO to produce 12. Finally, in keeping with the hypothesis offered in Scheme 1, 10a did act as a trimerizing catalyst toward diphenylacetylene (13) to yield 14. 

RXN48 Tandem Intramolecular Amination, Alkoxylation or Acyloxylation-Allylation of Alkynes and Allenes... 

A few interesting examples of allylations of alkynes have been described in the past decade. An intermolecular [2+2+1] carbonylative cocyclization between alkynes 175 and allyl halides 176 shows the versatile use of Ni catalysis for the construction of cyclic enone systems of type 177 (Scheme 12.83) [184]. 

Scheme 12.84 Nl-catalyzed cyanative allylation of alkynes with allyl cyanides (185).

Allylation of perfluoroalkyl halides with allylsilanes is catalyzed by iron or ruthenium carbonyl complexes [77S] (equation 119) Alkenyl-, allyl-, and alkynyl-stannanes react with perfluoroalkyl iodides 111 the presence ot a palladium complex to give alkenes and alkynes bearing perfluoroalkyl groups [139] (equation 120)... 

The masked propargylic anfz-l,3-diols obtained in these reactions are useful precursors to more functionalized systems. Lindlar reduction of alkyne 171 generated the (Z)-allylic diol 172, which underwent diastereoselective osmium tetraoxide-catalyzed dihydroxylation to provide the partially protected tetraol 173 (Scheme 28). The propargylic anfz-l,3-dioxane 175,obtained in 88% yield from... 

Morpholine also gives the allyhc amine in high yield. The reaction is thought to involve a known hydridopaUadium-catalyzed isomerization of alkynes to aUenes followed by reaction of the latter with the hydridopalladium complex to give 1-phenyl-substituted q -allylpalladium complexes. These complexes react with amines affording the allylic amines. Primary amines give the diallylic amines. An intramolecular version has been developed for the synthesis of 2-(2-phenyl)-pyrroUdines and -piperidines [319]. 

The catalyst reported by Grotjahn and Lev (11-13) for alkyne hydration (2) is capable of isomerizing alkenes, but veiy slowly. Because we knew that the rate of alkyne hydration was unchanged in the presence of excess phosphine ligand, we thought that like alkyne hydration, alkene isomerization would require loss of acetonitrile ligand (14) and alkene binding. Subsequent deprotonation at an allylic position would make an q -allyl intermediate which when reprotonated at the other... 

The heterogeneous catalytic system iron phthalocyanine (7) immobilized on silica and tert-butyl hydroperoxide, TBHP, has been proposed for allylic oxidation reactions (10). This catalytic system has shown good activity in the oxidation of 2,3,6-trimethylphenol for the production of 1,4-trimethylbenzoquinone (yield > 80%), a vitamin E precursor (11), and in the oxidation of alkynes and propargylic alcohols to a,p-acetylenic ketones (yields > 60%) (12). A 43% yield of 2-cyclohexen-l-one was obtained (10) over the p-oxo dimeric form of iron tetrasulfophthalocyanine (7a) immobilized on silica using TBHP as oxidant and CH3CN as solvent however, the catalyst deactivated under reaction conditions. 

Petasis reported an efficient addition of vinyl boronic acid to iminium salts.92 While no reaction was observed when acetonitrile was used as solvent, the reaction went smoothly in water to give allyl amines (Eq. 11.54). The reaction of the boron reagent with iminium ions generated from glyoxylic acid and amines affords novel a-amino acids (Eq. 11.55). Carboalumination of alkynes in the presence of catalytic Cp2ZrCl2 and H2O affords vinylalane intermediates, which serve as nucleophiles in the subsequent addition to enantiomerically enriched... 

Most studies on nickel-catalyzed domino reactions have been performed by Ikeda and colleagues [287], who observed that alkenyl nickel species, obtained from alkynes 6/4-41 and a (jr-allyl) nickel complex, can react with organometallics as 6/4-42. If this reaction is carried out in the presence of enones 6/4-43 and TM SCI, then coupling products such as 6/4-44 are obtained. After hydrolysis, substituted ketones 6/4-45 are obtained (Scheme 6/4.12). With cyclic and (5-substituted enones the use of pyridine is essential. Usually, the regioselectivity and stereoselectivity of the reactions is very high. On occasion, alkenes can be used instead of alkynes, though this is rather restricted as only norbornene gave reasonable results [288]. 

It is useful to consider the possible formulations of alkyne and allyl bonding to metals in terms of Green s MLX formalism.64 Coordination of an alkyne in a simple dative two-electron fashion is denoted ML, whereas the limit of metallacyclobutene formation is denoted MX2. For the allyl ligand, three imaginable coordinations are possible simple q1 coordination is denoted MX, butq3 coordination can encompass both MLX (one a bond plus a dative alkene coordination) and MX3 (three M—C a bonds). 

The very first example of the catalytic reductive cyclization of an acetylenic aldehyde involves the use of a late transition metal catalyst. Exposure of alkynal 78a to a catalytic amount of Rh2Co2(CO)12 in the presence of Et3SiH induces highly stereoselective hydrosilylation-cyclization to provide the allylic alcohol 78b.1 8 This rhodium-based catalytic system is applicable to the cyclization of terminal alkynes to form five-membered rings, thus complementing the scope of the titanocene-catalyzed reaction (Scheme 54). 

Similarly, 73-allylpalladium complexes were also employed as promoters for the cyclization.39,39a,39b The palla-dium(0)-catalyzed reaction of alkyne 168 with allylic carbonate in THF at 60 °G gave the A-allyl product 170 instead of the desired product 169. However, without isolation of 170, the reaction mixture was heated at 80 °G with 5 equiv. of K2CO3, providing 169 in 77% yield (Equation (7)). The nitrogen atom intervenes in the process as a nucleophile in the A-allylation step and as a leaving group in the cyclization step. 

Alkynes react with haloethenes [38] to yield but-l-en-3-ynes (55-80%), when the reaction is catalysed by Cu(I) and Pd(0) in the presence of a quaternary ammonium salt. The formation of pent-l-en-4-ynes, obtained from the Cu(I)-catalysed reaction of equimolar amounts of alk-l-ynes and allyl halides, has greater applicability and versatility when conducted in the presence of a phase-transfer catalyst [39, 40] although, under strongly basic conditions, 5-arylpent-l-en-4-ynes isomerize. Symmetrical 1,3-diynes are produced by the catalysed dimerization of terminal alkynes in the presence of Pd(0) and a catalytic amount of allyl bromide [41]. No reaction occurs in the absence of the allyl bromide, and an increased amount of the bromide also significantly reduces the yield of the diyne with concomitant formation of an endiyene. The reaction probably involves the initial allylation of the ethnyl carbanion and subsequent displacement of the allyl group by a second ethynyl carbanion on the Pd(0) complex. 

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