Alkynes to allenes

Isomerization of alkynes to allenes and then to conjugated dienes is catalyzed by Pd(0) species such as Pd(OAc)2 3.nd PhjP or Pdi(dba)3. The conjugated ketoalkyne 286 was converted into the conjugated dienone 287[141,I42]. 

The double phosphinylation of propargylic alcohols with diphenylphos-phine oxide to form 2,3-bis(diphenylphosphinyl)-1-propenes is catalyzed by a thiolate-bridged diruthenium complex (Scheme 28) [69]. It has been shown that the reaction proceeds via three ruthenium-catalyzed transformations propargylation of the phosphine oxide, alkyne to allene isomerization, and addition of phosphine oxide to the allene structure. 

Conjugated enynes. RuHjlPPhj) catalyzes the addition of alkynes to allenes. A ierrocenylphosphine is also used as ligand. 

All the organometallic alkynes rearrange along similar lines, both during reaction and, in some cases, spontaneously. The alkyne-to-allene interconversion is a consistent reaction of alkynes over a very wide range of substituents. 

The first examples of a Pd-catalyzed addition of terminal alkynes to allenes have been reported by Trost and Kottirsch (Scheme They observed that different palladium complexes efficiently catalyze the addition of terminal alkynes I to 3-substituted allenecarboxylates 23 to produce a mixture of the a,)8-unsaturated ester 24 and the two isomeric /S.-y-unsaturated esters (Z)- and (E)-25 (Scheme 9). Remarkably, the type of Pd catalyst used played a crucial role in determining the regiochemistry of addition to the 1,3-disubstituted allenes 23. Thus, with the Pd(OAc)2 TDMPP system (cat. A) a 76 24 ratio of 24 and E/Z)-25 was produced, whereas with a combination of tetrakis(carbo-methoxy)palladacyclopentadiene (TCPC) and TDMPP (cat. B) these products were obtained in a ratio of 9 91 (Scheme 9). ° ... 

Electrophilic additions to allenes represent an interesting reaction type which is related to additions to both alkenes and alkynes. An allene could, for example, conceivably be protonated at either a terminal s[p- carbon or the central sp carbon. 

Secondary amines can be added to certain nonactivated alkenes if palladium(II) complexes are used as catalysts The complexation lowers the electron density of the double bond, facilitating nucleophilic attack. Markovnikov orientation is observed and the addition is anti An intramolecular addition to an alkyne unit in the presence of a palladium compound, generated a tetrahydropyridine, and a related addition to an allene is known.Amines add to allenes in the presence of a catalytic amount of CuBr " or palladium compounds.Molybdenum complexes have also been used in the addition of aniline to alkenes. Reduction of nitro compounds in the presence of rhodium catalysts, in the presence of alkenes, CO and H2, leads to an amine unit adding to the alkene moiety. An intramolecular addition of an amine unit to an alkene to form a pyrrolidine was reported using a lanthanide reagent. 

The groups R2N and Cl can be added directly to alkenes, allenes, conjugated dienes, and alkynes, by treatment with dialkyl-V-chloroamines and acids. " These are free-radical additions, with initial attack by the R2NH- radical ion. " N-Halo amides (RCONHX) add RCONH and X to double bonds under the influence of UV light or chromous chloride. " Amines add to allenes in the presence of a palladium catalyst. ... 

Halogenation of alkenyl organometallic compounds Addition of hydrogen halides to triple bonds Halogenation of alkynes or allenes Addition of alkyl halides to triple bonds Addition of acyl halides to triple bonds... 

Nonstabilized carbonyl ylides (41) prepared by reaction of a-iodosilyl ethers with Smlj, can be trapped with various alkenes, alkynes and allenes to form furans of type 42, 43, and 44... 

AUylzirconium complexes are conveniently obtained by the regio- and stereoselective hydrozirconation of allene [127-133] and can be, for example, used subsequently for the MAO-catalyzed allylzirconation of alkynes to prepare enyne derivatives [132]. Alternatively, the preparation of (E)-l,3-dienes from aldehydes and the appropriate allylstannane zirconocene derivative (R = SnBu,) is accomplished (Scheme 8-17) [131], Note that addition of [Cp2Zr(H)Cl[n (1) on the aUenyl reagent with the... 

Another versatile domino process for the synthesis of carbocycles as well as heterocycles is the Pd-catalyzed reaction of organic halides or triflates with alkynes or allenes, which contain a carbo- or heteronucleophile in close vicinity to these functionalities (see Scheme 6/1.75) [133]. 

Organometallic complexes of the /-elements have been reported that will perform both intra-and intermolecular hydroamination reactions of alkenes and alkynes, although these lie outside of the scope of this review.149-155 Early transition metal catalysts are not very common, although a number of organometallic systems exist.156-158 In these and other cases, the intermediacy of a metal imido complex LnM=NR was proposed.159,160 Such a species has recently been isolated (53) and used as a direct catalyst precursor for N-H addition to alkynes and allenes (Scheme 35).161,162... 

Intramolecular nucleophilic additions by nitrogen functional groups onto pendant alkynes and allenes represent an important class of type la approaches to functionalized pyrroles. A platinum-catalyzed (PtCl4) cyclization of homopropargyl azides provided an entry to 2,5-disubstituted pyrroles and 4,5,6,7-tetrahydroindoles (fused pyrroles) <06OL5349>. 

The photochemical addition of diphenyl(trimethylstannyl)phosphine to either alkynes or allenes has been investigated23. The -isomer is usually predominant (reaction 9) except... 

Such reactions involve the addition of organometallic reagent to unsaturated systems like alkynes, alkenes, allenes, or related structures in order to create a new C-C bond and C-M bond at the same time. The C-M bond can then be functionalized by an electrophile to generate a wide range of products. 

Carbon dioxide instead of aldehydes can be involved in Ni(0)-promoted reductive coupling reactions (Equations (76) and (77) Scheme 90).434,434a 434c A stoichiometric amount of Ni(COD)2/DBU reacts with C02 and dienes, alkynes, or allenes to afford a metallacycle intermediate. This metallacycle reacts with organozinc compounds or aldehydes in one-pot to give carboxylic acid derivatives. As shown in Scheme 90, double carboxylation occurs in the presence of dimethylzinc, where the stereochemical outcome is opposite to that of the reaction with diphenylzinc. 

Rhodium complexes catalyze hydrosilylation-cyclization of 1,6-allenynes in the presence of (MeO SiH.77 To avoid complex product distributions, the use of substrates possessing fully substituted alkyne and allene termini is imperative. As shown in the cyclization of 1,6-allenyne 62a, the regiochemistry of silane incorporation differs from that observed in the rhodium-catalyzed hydrosilylation-cyclization of 1,6-enynes (see Section 10.10.2.3.2). For allenyne substrates, allene silylation occurs in preference to alkyne silylation (Scheme 40). 

As seen in Scheme 55, with the simple addition of a balloon of CO to the [5 + 2]-reaction of VCPs and alkynes or allenes, the [5 + 2]-reaction can be diverted via a nine-membered metallacycle to produce initially an eight-membered ring product. This Rh(l)-catalyzed three-component [5 + 2 + l]-reaction is mechanistically similar to the previously mentioned [6 + 2]-reaction (Section 10.13.2.5.2) differing only in regard to the insertion of CO in the pathway versus its incorporation in starting material (Scheme 56). 

In addition to alkenes and alkynes, allenes have attracted considerable interest due to their unique reactivity and multireaction sites. Therefore, transition-metal-catalyzed nucleophilic addition reaction of amines and imines to allenes has been extensively studied to prepare biologically important amines and nitrogen-heterocycles.31,31d... 

Carbostannation of alkynes and allenes has recently been developed and provides an important new route to stannylalkenes (Equation (35)). 

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