Die palladiumkatalysierte Cocyclisierung von Allenen mit elektronenarmen Alkinen. Einige Untersuchungen zur Kupplung von Allenderivaten mit Acetylendicarbonsäuredimethylester an Palladium und Platin
“…tom Dieck's group reported the synthesis of tetrasubstituted naphthalene ester 635 , an important class of organic compounds for the preparation of polyimides from the reaction of 2 mol of allenes with 2 mol of acetylene dicarboxylate 632 in the presence of diazadiene-stabilized palladacyclopentadiene 633 as the catalyst (Scheme ). Compound 635 can be obtained from the reaction of 1,2-propadiene ( 40 ) in high yield by a two-step procedure and by a novel one-step procedure from allenic ethers 232 and 630 , of course in diminished yields, both via 634 . , Interestingly, in the case of phenoxyallene ( 631 ) and methylallene 533 , no 635 but cotrimerization product 636 was formed, possibly due to steric reasons. 172 …”
Section: Di- Oligo- and Polymerization Reactions Of
Allenesmentioning
confidence: 99%
“…Compound 635 can be obtained from the reaction of 1,2-propadiene (40) in high yield by a two-step procedure and by a novel one-step procedure from allenic ethers 232 and 630, of course in diminished yields, both via 634. 192,193 Interestingly, in the case of phenoxyallene (631) and methylallene 533, no 635 but cotrimerization product 636 was formed, possibly due to steric reasons. Do ¨hring and Jolly studied the palladium-catalyzed co-oligomerization of 1,2-propadiene (40) and carbon dioxide leading to a mixture of esters 637 and 639, δ-lactone 638, hydrocarbon oligomers, and polymer (Scheme 173).…”
Section: Di- Oligo- and Polymerization Reactions Of Allenesmentioning
“…tom Dieck's group reported the synthesis of tetrasubstituted naphthalene ester 635 , an important class of organic compounds for the preparation of polyimides from the reaction of 2 mol of allenes with 2 mol of acetylene dicarboxylate 632 in the presence of diazadiene-stabilized palladacyclopentadiene 633 as the catalyst (Scheme ). Compound 635 can be obtained from the reaction of 1,2-propadiene ( 40 ) in high yield by a two-step procedure and by a novel one-step procedure from allenic ethers 232 and 630 , of course in diminished yields, both via 634 . , Interestingly, in the case of phenoxyallene ( 631 ) and methylallene 533 , no 635 but cotrimerization product 636 was formed, possibly due to steric reasons. 172 …”
Section: Di- Oligo- and Polymerization Reactions Of
Allenesmentioning
confidence: 99%
“…Compound 635 can be obtained from the reaction of 1,2-propadiene (40) in high yield by a two-step procedure and by a novel one-step procedure from allenic ethers 232 and 630, of course in diminished yields, both via 634. 192,193 Interestingly, in the case of phenoxyallene (631) and methylallene 533, no 635 but cotrimerization product 636 was formed, possibly due to steric reasons. Do ¨hring and Jolly studied the palladium-catalyzed co-oligomerization of 1,2-propadiene (40) and carbon dioxide leading to a mixture of esters 637 and 639, δ-lactone 638, hydrocarbon oligomers, and polymer (Scheme 173).…”
Section: Di- Oligo- and Polymerization Reactions Of Allenesmentioning
“…The poor results achieved with other palladium(II) catalysts, reflected by the low (11−39%) yields of lactone 6a , and the precipitation of palladium(0) (entries 6−9, Table ), highlighted the importance of the “nontransferable” auxiliary allyl ligand for stabilizing the catalytic intermediates and mediating an efficient allyl transfer. An initial oxidative cyclization of allenyl ester 3a mediated by the palladium(0) complex (Pd 2 dba 3 ) giving rise to a metalacycle with palladium in oxidation state Pd(II), could rationalize the formation of small quantities of lactone 6a (23%, entry 10, Table ). Lactone 6a was obtained in 20% and 23% enantiomeric excess from reactions catalyzed by nonracemic complexes 1a and 1b , respectively (entries 1 and 6, Table ).…”
A palladium-catalyzed regioselective bisfunctionalization of allenyl esters with boronic acids (nucleophiles) and aldehydes (electrophiles) was demonstrated. The three-component coupling afforded alpha,beta-unsaturated delta-lactones under mild conditions and with excellent chemo-, regio-, and diastereoselectivity. Aromatic, heteroaromatic and vinylic boronic acids (R1B(OH)2) reacted with ethyl 2,3-butadienoate and benzaldehyde to afford the corresponding 4-R(1),6-Ph-disubstituted alpha,beta-unsaturated delta-lactones in 62-78% yields. Lactones derived from aromatic, heteroaromatic, and vinylic aldehydes were isolated in 51-58% yields, while aliphatic aldehydes were less reactive. The regiochemistry of bisfunctionalization of allenyl ester homologues remained controlled by the ester substituent, and the reactions afforded cis-4,5,6-trisubstituted alpha,beta-unsaturated delta-lactones and esters of (Z)-syn-3,4,5-trisubstituted-5-hydroxy-2-pentenoic acids in combined 47-65% yields. The superior performance of a pi-allylpalladium(II) dimer catalyst featuring an auxiliary allyl ligand derived from beta-pinene, among diverse palladium(II) catalysts, was demonstrated. A catalytic cycle involving an unsymmetrical bis-pi-allylpalladium complex as the key intermediate was proposed, and the communication highlights the synthetic potential of such intermediates. However, the efficiency of asymmetry transfer remained low (<20%).
“…28 When increasing the temperature to 60 1C and increasing the catalyst loading, the benzene derivative was obtained quantitatively. 29 The authors postulate that the benzene derivative is formed after an isomerisation process of the initially formed 1,3-cyclohexadiene derivative. Takahashi et al 30 also used a metallacyclopentadiene for the [2+2+2] cycloaddition reaction although in this case as a substrate.…”
Section: Intermolecular and Partially Intermolecular Cycloadditions Omentioning
The development of efficient reactions that enable the construction of multiple bonds and/or stereogenic centres in a single synthetic operation is of great interest for greener and step-economical syntheses of complex organic targets. Transition-metal-catalysed [2+2+2] cycloadditions excell in this regard: no fewer than three new sigma bonds and a new ring system are formed from simple unsaturated components. Allenes constitute an important subclass among these. They are more reactive than simple alkenes and generate sp(3) centres, with important stereochemical implications. In addition, further manipulation of the resulting cycloadduct through the remaining double bond is possible, increasing molecular complexity. This tutorial review highlights the value that allenes have as reagents in [2+2+2] cycloaddition and their great versatility for the development of methods to generate complex architectures.
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