Platinum-Catalyzed Cycloisomerization Reactions of Enynes

Fürstner, Alois; Stelzer, Frank; Szillat, Hauke

doi:10.1021/ja0109343

Cited by 423 publications

(187 citation statements)

References 28 publications

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“…[8,9] The results are summarized in Scheme 7. In addition to the formation of 10-membered dienes 25, 26, 28, 31 and 32, the cycloisomerization was suitable for production of bicyclic products containing 12-membered dienes and 14-membered tetraenes (27 and 29).…”

Section: Scheme 2 a C H T U N G T R E N N U N G (Pphmentioning

confidence: 99%

“…They found that treatment of these substrates with a catalytic amount of PtCl 2 at elevated temperature (60-80 8C in toluene) resulted in the assembly of the corresponding azabicyclo-[4.1.0]heptenes (Scheme 16). [8,9] Mono-, di-, and trisubstituted alkenes efficiently participated in this process.…”

Section: Formation Of Bicycloa C H T U N G T R E N N U N G [410]hepmentioning

confidence: 99%

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Gold and Platinum Catalysis of Enyne Cycloisomerization

2006

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This account provides a comprehensive overview of the development of gold and platinum catalysis of the enyne cycloisomerization. The use of these soft, alkynophilic metals enables mild, chemoselective and efficient transformations of a variety of readily available acyclic enynes to a wide range of synthetically useful carbocyclic and heterocyclic products. The review is organized according to diverse structural types of enynes that undergo skeletal cycloisomerizations. The account begins with an overview of transformations of primarily 1,6-enynesheptenes. This section is followed by the discussion of cycloisomerizations of 1,5-enynes, which enable a rapid access to a range of other cyclic products, including bicycloA C H T U N G T R E N N U N G [3.1.0]hexenes, cyclohexadienes, heterobicycloalkenes, methylenecyclopentenes, naphthalenes and methyleneindenes. In addition, the [3,3] rearrangement of 1,5-enynes provides efficient access to the corresponding allenes. The account concludes with an overview of the most recent studies on gold-and platinum-catalyzed cycloisomerizations of 1,4-and 1,3-enynes. Due to the rapidly increasing interest in this area during the past three to five years, we believe that this review provides a timely and comprehensive discussion of the development gold-and platinum-catalyzed cycloisomerization starting from the initial pioneering investigations to the latest advances in the field. A significant emphasis is placed on the mechanistic discussion of the observed manifolds of skeletal reorganizations.

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Section: Scheme 2 a C H T U N G T R E N N U N G (Pphmentioning

confidence: 99%

Section: Formation Of Bicycloa C H T U N G T R E N N U N G [410]hepmentioning

confidence: 99%

Gold and Platinum Catalysis of Enyne Cycloisomerization

2006

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“…On the basis of these data, we propose the process detailed in Scheme 1 as the most likely mechanism for this transformation. Coordination of cationic gold(I) to the alkyne followed by nucleophilic addition of the pendant olefin produces cyclopropylcarbinyl 13 cation 27, which may have some gold(I) carbene character (28). The bicyclo[3.1.0]hexene product is generated by a 1,2-hydrogen shift onto a cation or a gold(I) carbene.…”

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confidence: 99%

Catalaytic Isomerization of 1,5-Enynes to Bicyclo[3.1.0]hexenes

2004

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Transition metal-catalyzed isomerization and rearrangement reactions of unsaturated systems provide access to structural motifs not accessible through their thermal counterparts. This is exemplified by the numerous applications of transition metal-catalyzed Alder-ene reactions of 1,6-and 1,7-enynes for the synthesis of cyclopentyl and cyclohexyl ring systems. 1 The corresponding skeletal rearrangements of simple 1,5-enynes are much less studied. Berson and co-workers conjectured that the thermal rearrangement of 1,5-enyne 1 proceeds via bicyclo[3.1.0]hexene 2 to afford toluene and triene 3 as the major constituents of a complex mixture. 2 Scattered reports of transition metal-catalyzed isomerizations of 1,5-enynes 3 exist; however, these generally employ enol ethers as the ene component. 4,5 While enols are expected to be excellent nucleophiles, 6 we were intrigued by the possibility that metal-alkyne complexes could be electrophilic enough to react even with simple olefins and catalyze processes related to the thermal rearrangement.To this end, treatment of 1,5-enyne 4 with 1 mol % palladium-(II) or platinum(II) complexes returned mainly starting material (eq 2). Both silver(I) tetrafluoroborate and triphenylphosphinegold(I) chloride failed to catalyze the rearrangement of 4. On the other hand, the combination of these two complexes 7 rapidly (5 min) and cleanly produced bicyclo[3.1.0]hexene 8 5, an olefin isomer of the proposed intermediate (2) in the thermal isomerization. In sharp contrast to the gold(I)-catalyzed cyclizations of ω-alkynyl -ketoesters, 9 none of the competing 5-exo-dig cyclization to afford an exo-methylene product was observed. Finally, gold(III) chloride also catalyzed this reaction, however, with significantly lower conversion. On the other hand, 5% AuCl 3 with 15% AgOTf gave complete conversion; however, this was accompanied by a substantial amount of decomposition.

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“…The stereochemical course of the reaction may lead to the formation of three diastereoisomers; the relative orientation of the substituents on the spiro-fused lactones may be defined as symmetrical-syn, unsymmetrical and symmetrical-anti. [17] The X-ray structure confirms the stereochemistry as the symmetrical-syn diastereoisomer, which occupies an unusual higher Table 2. Further isomerisation of 2a and 2b by monocationic Pd(II).…”

Section: Anion Effectsmentioning

confidence: 64%

Phosphinite Ligand Effects in Palladium(II)‐Catalysed Cycloisomerisation of 1,6‐Dienes: Bicyclo[3.2.0]heptanyl Diphosphinite (B[3.2.0]DPO) Ligands Exhibit Flexible Bite Angles, an Effect Derived from Conformational Changes (exo‐ or endo‐Envelope) in the Bicyclic Ligand Scaffold

et al. 2006

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Changes in bidentate ligand structure significantly affect catalytic activity in mono-cationic Pd(II)-catalysed 1,6-diene cycloisomerisation processes to give cyclopentene products. A bicyclo-is the first phosphorus-based bidentate ligand capable of promoting regioselective 1,6-diene cycloisomerisation. Trace quantities of water are essential for catalytic activity, as is the precise order of mixing of 1,6-diene, Pd(II) pro-catalyst and additives. Conformational changes in the ligand backbone seem to be important in stabilising the active catalyst species, assumed to be a cationic Pd(II) hydride species. DFT calculations support a change in bite angle on the cationic Pd(II) hydride species from circa 908 (cis) to 1708 (trans); in the latter geometry an agostic interaction of the C4 endo hydrogen of the bicyclic ringsystem with Pd(II) stabilises the cationic metal centre. This unique ligand property could be exploited in other transition metal catalysed processes.

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Platinum-Catalyzed Cycloisomerization Reactions of Enynes

Cited by 423 publications

References 28 publications

Gold and Platinum Catalysis of Enyne Cycloisomerization

Gold and Platinum Catalysis of Enyne Cycloisomerization

Catalaytic Isomerization of 1,5-Enynes to Bicyclo[3.1.0]hexenes

Phosphinite Ligand Effects in Palladium(II)‐Catalysed Cycloisomerisation of 1,6‐Dienes: Bicyclo[3.2.0]heptanyl Diphosphinite (B[3.2.0]DPO) Ligands Exhibit Flexible Bite Angles, an Effect Derived from Conformational Changes (exo‐ or endo‐Envelope) in the Bicyclic Ligand Scaffold

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