Ring‐Closing Alkyne Metathesis in Natural Product Synthesis

Davies, Paul W.

doi:10.1002/9783527629626.ch7

Cited by 18 publications

(3 citation statements)

References 79 publications

(38 reference statements)

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“…Acetylene scission by highly reactive metal complexes has been discovered for the ditungsten hexaalkoxide [W 2 (O t Bu) 6 ] with a WW triple bond and produces alkylidyne complexes [( t BuO) 3 WCR] in clean reactions with a variety of substituted alkynes under mild conditions . Recent review articles on the utility of alkyne metathesis with alkylidyne complexes in synthetic organic chemistry have been provided by Fürstner and other authors. − A combined coupling and scission reaction of diphenylacetylene ligands in a mononuclear tungsten complex aided by a fullerene ligand has been observed recently . Diphenylacetylene scission with formation of the μ 4 -benzylidyne ligands of the hexanuclear cluster [(CpMo) 2 Co 4 (μ 4 -CPh) 2 (μ-CO) 2 (CO) 8 ] has been reported in 2002, and more alkyne scission reactions in cluster chemistry are the subject of a review article .…”

Section: Alkylidyne Complexesmentioning

confidence: 99%

Benzylidyne Bridges from Diphenylacetylene and a Methylidyne Bridge from Methylmagnesium Chloride

et al. 2015

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Preparation of the dimeric starting compound [(C5H2 tBu3-1,2,4)Fe(μ-Br)]2 (1) gave a small amount of its green sodium bromide adduct [(C5H2 tBu3-1,2,4)Fe(μ-Br)2Na(DME)2] (2). Reduction of 1 under argon in the presence of diphenylacetylene yielded dark red [(C5H2 tBu3-1,2,4)Fe(μ-CPh)]2 (3) containing two bridging benzylidyne ligands resulting from diphenylacetylene scission. The dicobalt methylidyne complex [{(C5HiPr4)Co}2(μ-CH)(μ-H)] (5) was obtained in high yield from the reaction of [(C5HiPr4)Co(μ-Cl)]2 (4) with two equivalents of methylmagnesium chloride. According to DFT calculations the dinuclear alkylidyne complexes 3 and 5 contain d6 metal centers, namely, iron(II) (3) and cobalt(III) (5). Whereas the benzylidyne ligands of the iron complex 3 display an empty orbital of p z character at the bridging carbon atom, the p z orbital of the methylidyne carbon in the dicobalt complex 5 is filled with a lone pair of electrons.

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Section: Alkylidyne Complexesmentioning

confidence: 99%

Benzylidyne Bridges from Diphenylacetylene and a Methylidyne Bridge from Methylmagnesium Chloride

et al. 2015

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“…Transition metal-catalyzed alkyne cross metathesis (ACM), [1][2][3][4][5][6][7][8][9][10][11][12] nitrile-alkyne cross metathesis (NACM), 1,[13][14][15][16][17][18][19][20] ring-closing alkyne metathesis (RCAM), [21][22][23][24] ring-opening alkyne metathesis polymerization (ROAMP), [25][26][27][28] and acyclic diyne metathesis (ADIMET) [29][30][31] continue to attract considerable interest as useful catalytic methods for creating CuC triple bonds. Work still remains to create highly active catalysts that tolerate a broad scope of substrates comparable to their alkene metathesis counterparts.…”

Section: Introductionmentioning

confidence: 99%

Unusually stable tungstenacyclobutadienes featuring an ONO trianionic pincer-type ligand

et al. 2013

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This report presents the synthesis of the first neutral trianionic ONO pincer-type tungsten alkylidyne complex, [CF(3)-ONO]W≡C((t)Bu)(OEt(2)) (5) {where CF(3)-ONO = (MeC(6)H(3)[C(CF(3))(2)O])(2)N(3-)}. Treating 5 with 1-phenylpropyne, 4,4-dimethyl-2-pentyne, and cyclooctyne yields the corresponding tungstenacyclobutadiene complexes [CF(3)-ONO]W[κ(2)-C((t)Bu)C(Me)C(Ph)] (6), [CF(3)-ONO]W[κ(2)-C((t)Bu)C(Me)C((t)Bu)] (7), and [CF(3)-ONO]W[κ(2)-C((t)Bu)C(CH(2))(6)C] (8). Complexes 6, 7, and 8 do not undergo retro-[2 + 2]-cycloaddition even at 200 °C or in the presence of PMe(3). DFT methods to elucidate the electronic structure of complexes 5 and 6 reveal important electronic factors that contribute to the lack of reactivity for the tungstenacyclobutadienes. An important bonding combination between the pincer N-atom lone pair and the W[triple bond, length as m-dash]C bond within 5, termed an inorganic enamine, provides an explanation for the lack of retro-[2 + 2]-cycloaddition from 6, 7, and 8. (15)N NMR spectroscopy was used to confirm the computational finding of an inorganic enamine bonding combination. Single crystal X-ray analysis of 5, 6, 7, and 8 provides insight into possible steric inadequacies within the CF(3)-ONO(3-) ligand to promote catalytic metathesis.

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“…Triggered by Fürstner’s groundbreaking work on RCAM in the field of natural product synthesis (for early examples, see in [ 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 ]; for more recent examples, see in [ 23 , 79 , 80 , 81 ], we reasoned that this method would be a promising alternative to RCM. (For a review on the use of RCAM in natural product synthesis, see in [ 82 ].) Thus, macrocyclization was planned to be achieved by RCAM at C(9)/C(10), i.e., at the same site that was initially foreseen for RCM, leading to diyne 113 as the ultimate cyclisation precursor ( Scheme 18 ).…”

Section: Resultsmentioning

confidence: 99%

Ring-Closing Metathesis Approaches towards the Total Synthesis of Rhizoxins

2020

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Efforts are described towards the total synthesis of the bacterial macrolide rhizoxin F, which is a potent tubulin assembly and cancer cell growth inhibitor. A significant amount of work was expanded on the construction of the rhizoxin core macrocycle by ring-closing olefin metathesis (RCM) between C(9) and C(10), either directly or by using relay substrates, but in no case was ring-closure achieved. Macrocycle formation was possible by ring-closing alkyne metathesis (RCAM) at the C(9)/C(10) site. The requisite diyne was obtained from advanced intermediates that had been prepared as part of the synthesis of the RCM substrates. While the direct conversion of the triple bond formed in the ring-closing step into the C(9)-C(10) E double bond of the rhizoxin macrocycle proved to be elusive, the corresponding Z isomer was accessible with high selectivity by reductive decomplexation of the biscobalt hexacarbonyl complex of the triple bond with ethylpiperidinium hypophosphite. Radical-induced double bond isomerization, full elaboration of the C(15) side chain, and directed epoxidation of the C(11)-C(12) double bond completed the total synthesis of rhizoxin F.

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Ring‐Closing Alkyne Metathesis in Natural Product Synthesis

Cited by 18 publications

References 79 publications

Benzylidyne Bridges from Diphenylacetylene and a Methylidyne Bridge from Methylmagnesium Chloride

Benzylidyne Bridges from Diphenylacetylene and a Methylidyne Bridge from Methylmagnesium Chloride

Unusually stable tungstenacyclobutadienes featuring an ONO trianionic pincer-type ligand

Ring-Closing Metathesis Approaches towards the Total Synthesis of Rhizoxins

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