Chemoselective Construction of Substituted Conjugated Dienes Using an Olefin Cross-Metathesis Protocol

Funk, Timothy W.; Efskind, Jon; Grubbs, Robert H.

doi:10.1021/ol047929z

Cited by 120 publications

(51 citation statements)

References 21 publications

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“…Grubbs has also described a highly E-stereoselective alkene-diene cross-metathesis using 2-substituted-1,3-butadienes. 73 The 2-butadiene starting materials can be accessed by ethylene-alkyne cross-metathesis (equation 24). …”

Section: Ethylene-assisted Ceymmentioning

confidence: 99%

5.27 Ene–Yne Metathesis

Diver

Clark

2014

Comprehensive Organic Synthesis II

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Section: Ethylene-assisted Ceymmentioning

confidence: 99%

5.27 Ene–Yne Metathesis

Diver

Clark

2014

Comprehensive Organic Synthesis II

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“…[6][7] Boryl-substituted 1,3-dienes can be prepared by classic stoichiometric routes using organometallic reagents [10,11] or by more recently applied catalytic methods, such as hydroboration of enynes, [12] cross-coupling of 1,1-diborylated alkenes with alkenyl halides, [13] Heck coupling of vinylboronate with vinylarylic iodides, [8e, 14] as well as cross-metathesis of vinylboronates with 1,3-dienes. [15] Additionally, silylboryl-substituted dienes can be synthesised by means of nickel-catalysed silaborative dimerisation of alkynes. [16] Herein we report a new catalytic transformation of vinylsubstituted boronates with selected terminal ethynes (also silylethynes) occurring in the presence of ruthenium complexes containing the Ru À H bond.…”

Section: Introductionmentioning

confidence: 99%

A New Catalytic Route to Boryl‐ and Borylsilyl‐Substituted Buta‐1,3‐dienes

Walkowiak

Jankowska‐Wajda

Marciniec

2008

Chemistry A European J

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Vinyl-substituted boronates in the presence of complexes containing Ru-H bonds (preferably [Ru(CO)ClH(PCy(3))(2)], Cy: cyclohexyl) react regioselectively with terminal ethynes (involving silylethynes), albeit with the exception of phenylacetylene, to produce boryl- and borylsilyl-substituted buta-1,3-dienes with a preference for E,E-diene. The reaction opens a new catalytic route for the preparation of dienylboronates, and particularly dienylsilylboronates, that are functionalised building blocks in the synthesis of organic and natural products. The mechanism of this new reaction was proved to involve an insertion of alkyne into Ru-H bonds followed by an insertion of coordinated vinyl boronate into the Ru-C= bond and beta-hydrogen transfer to the metal to eliminate boryldiene or borylsilyldiene.

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“…5g,j So far, total syntheses of the macrocycle of rhizopodin have employed either intramolecular Suzuki coupling reaction or macrolactonization. 5g-j An alternative approach to the macrocyclizations was sought and we opted to close the macrocyclic core by ene-diene cross-metathesis 6 as shown in our retrosynthetic plan (Scheme 1). To test the feasibility of the key ene-diene cross-metathesis step of our designed strategy toward rhizopodin, a model study based on the construction of the C1-C15 fragment (1) of rhizopodin was undertaken.…”

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confidence: 99%

Cross-Metathesis Approach for Stereocontrolled Synthesis of the C1–C15 Fragment of Rhizopodin

Gui

Liu

Song

et al. 2013

Synlett

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Abstract:The C1-C15 fragment of rhizopodin was synthesized through either Suzuki coupling reaction of vinyl iodide and vinyl boronate or cross-metathesis of a terminal olefin and a diene adduct in the presence of Hoveyda-Grubbs II catalyst.Key words: cross-metathesis, cross-coupling, stereocontrolled synthesis, conjugated diene, rhizopodin Rhizopodin was isolated by Höfle and Reichenbach from the myxobacterium Myxococcus stipitatus and was assigned as a monomeric lactone in 1993. 1 Its structure and absolute stereochemistry were recently revised as shown in Scheme 1. 2,3 Rhizopodin exhibits significant biological properties including potent cytostatic activity in the low nanomolar range against a range of tumor cell lines. [1][2][3] The distinctive structural features and biological activities, together with our interest in macrocyclic marine natural products 4 prompted us to undertake studies on the synthesis of rhizopodin. Recently, various synthetic approaches toward the synthesis of rhizopodin have been reported. 5 The syntheses of monorhizopodin and 16-epimonorhizopodin were achieved by Nicolaou and coworkers in 2011 5e and, since then, two total syntheses of rhizopodin have been reported. 5g,j So far, total syntheses of the macrocycle of rhizopodin have employed either intramolecular Suzuki coupling reaction or macrolactonization. 5g-j An alternative approach to the macrocyclizations was sought and we opted to close the macrocyclic core by ene-diene cross-metathesis 6 as shown in our retrosynthetic plan (Scheme 1). To test the feasibility of the key ene-diene cross-metathesis step of our designed strategy toward rhizopodin, a model study based on the construction of the C1-C15 fragment (1) of rhizopodin was undertaken. Herein we detail two synthetic approaches to fragment 1. Retrosynthetic analysis of 1 led us to disconnect between positions C8 and C9, which imposed the construction of the conjugated diene through cross-metathesis of fragments 2 and 3. Alternatively, a Suzuki cross-coupling of vinyl boronate 4 with vinyl iodide 5 was envisioned to deliver diene 1 (Scheme 1). Oxazole-containing fragments 2 and 4 were planned to originate from the common precursor 10, which, in turn, would be prepared from the known methyl-2-(chloromethyl)oxazole-4-carboxylate (7; Scheme 2). The synthesis of fragments 2 and 4 is outlined in Scheme 2. Oxazole 7 was obtained from commercially available 2,2-dichloronitrile (6) by using a known sequence. 7 Reaction of 7 with sodium acetate in the presence of acetic acid and acetic anhydride and treatment of the resultant acetate derivative with potassium carbonate and methanol afforded the corresponding alcohol 8 in 61% yield over two steps. After protection of the primary alcohol as its TBS ether, the methyl ester was reduced with DIBAL-H in THF to give alcohol 9 in 84% yield. This route is operationally convenient and proceeds well on large scale (>35 g of 9 was obtained). It should be mentioned that alcohol 9 could be obtained by a reported procedure; 8 however, in our hands...

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Chemoselective Construction of Substituted Conjugated Dienes Using an Olefin Cross-Metathesis Protocol

Cited by 120 publications

References 21 publications

5.27 Ene–Yne Metathesis

5.27 Ene–Yne Metathesis

A New Catalytic Route to Boryl‐ and Borylsilyl‐Substituted Buta‐1,3‐dienes

Cross-Metathesis Approach for Stereocontrolled Synthesis of the C1–C15 Fragment of Rhizopodin

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