Highly selective cross-metathesis of terminal olefins

Crowe, William E.; Zhang, Zhijia J.

doi:10.1021/ja00076a071

Cited by 120 publications

(45 citation statements)

References 3 publications

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“…The allylic sulfide 1c and sulfone probes 1 d produced the homodimers 2 c and 2 d in high yields, respectively. In contrast, the vinyl substrate 1 b produced only a trace quantity of homodimer 2 b even after extended reaction time (12 hours), consistent with expectations for substituted styrenes …”

Section: Figuresupporting

confidence: 84%

“…In contrast, the vinyl substrate 1 b produced only a trace quantity of homodimer 2 b even after extended reaction time (12 hours), consistent with expectations for substituted styrenes. [15] The alkene 2-methyl-2-butene (1 S) is a convenient substrate for the preparation of isoprenoid derivatives due to its volatility (35-38°C), that enables the use of excess reagent to drive a cross-metathesis event towards complete conversion. [16,17] Comparative reactions of the alkenyl probes 1 b, 1 c, and 1 d were conducted using 100 equivalents of 2-methyl-2butene and 5 mol % of the HG(II) catalyst in dichloromethane at 40°C (Equation 1).…”

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confidence: 99%

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Bimolecular Cross‐Metathesis of a Tetrasubstituted Alkene with Allylic Sulfones

et al. 2019

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Exquisite control of catalytic metathesis reactivity is possible through ligand‐based variation of ruthenium carbene complexes. Sterically hindered alkenes, however, remain a generally recalcitrant class of substrates for intermolecular cross‐metathesis. Allylic chalcogenides (sulfides and selenides) have emerged as “privileged” substrates that exhibit enhanced turnover rates with the commercially available second‐generation ruthenium catalyst. Increased turnover rates are advantageous when competing catalyst degradation is limiting, although specific mechanisms have not been defined. Herein, we describe facile cross‐metathesis of allylic sulfone reagents with sterically hindered isoprenoid alkene substrates. Furthermore, we demonstrate the first example of intermolecular cross‐metathesis of ruthenium carbenes with a tetrasubstituted alkene. Computational analysis by combined coupled cluster/DFT calculations exposes a favorable energetic profile for metallacyclobutane formation from chelating ruthenium β‐chalcogenide carbene intermediates. These results establish allylic sulfones as privileged reagents for a substrate‐based strategy of cross‐metathesis derivatization.

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Section: Figuresupporting

confidence: 84%

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confidence: 99%

Bimolecular Cross‐Metathesis of a Tetrasubstituted Alkene with Allylic Sulfones

et al. 2019

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“…The cross-metathesis of 4-bromostyrene and 4-methoxystyrene was repeated with a ten-fold excess of styrene in order to improve the selectivity toward the unsymmetrical product. [6,7,16] These conditions efficiently and selectively produced the unsymmetrical products (AB) with high conversions along with the formation of stilbene (BB) and almost no self-metathesis (AA) of the reagent used in default was observed ( Table 3).…”

mentioning

confidence: 98%

Simple Ruthenium Precatalyst for the Synthesis of Stilbene Derivatives and Ring‐Closing Metathesis in the Presence of Styrene Initiators

Cariou

Fischmeister

et al. 2007

Adv Synth Catal

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was found to be an efficient precatalyst, with styrene as an initiating species, for the alkene metathesis of various styrenes into symmetrical and unsymmetrical stilbene derivatives and for the ring-closing metathesis reaction of a sterically hindered olefin leading to a tetrasubstituted cycloolefin.Keywords: alkene metathesis; N-heterocyclic carbenes; ring-closing metathesis; ruthenium; stilbenes; styrenes Stilbene derivatives, in particular hydroxy-or alkoxysubtituted ones are gaining importance due to their biological activities for the prevention of cancer or cardiovascular diseases.[1] They are also an important family of building blocks for the design of conjugated materials with optical properties.[2] Wittig or WittigHorner reactions [3] constitute a priviledged approach for the synthesis of stilbene derivatives but they generate stoichiometric amounts of phosphine oxides hence requiring fastidious purification. Catalytic reactions such as Heck or Suzuki couplings can be used as more efficient ways to synthesize stilbene derivatives.[4] More recently catalytic olefin metathesis [5] appeared as a tool of choice for the efficient and stereoselective synthesis of stilbene derivatives thanks to the emergence of very active catalysts for cross-metathesis.[6] In particular, the ruthenium-based second generation Grubbs catalyst has been shown to efficiently promote the self-and cross-metathesis of styrene derivatives. [7] Other complexes based on molybdenum [8] or osmium [9] have also been described as efficient catalysts for this transformation.We recently reported the intramolecular vinyl C À H bond activation of an N-vinyl-N-heterocyclic carbeneruthenium(II) intermediate leading to a bidentate NHC-alkenyl ruthenium complex (Scheme 1). [10] In an attempt to explore the intermolecular version of this transformation, styrene was reacted with the readily available ruthenium complex[11] [IMes = 1,3bis(2,4,6-trimethylphenyl)imidazol-2-ylidene]. This reaction resulted in the stereoselective formation of E-stilbene in very good yield, thus suggesting a self-metathesis reaction. Here we describe several aspects of RuCl 2 A C H T U N G T R E N N U N G (p-cymene)-A C H T U N G T R E N N U N G (IMes) as catalyst precursor for alkene metathesis reactions. In the absence of an alkene metathesis carbene initiator, complex 1 acts as a pre-catalyst for the metathesis transformation of various styrene derivatives into the corresponding stilbenes including unsymmetrical ones. We show the dual ring-closing metathesis (RCM) vs. cycloisomerisation activity of 1 and that, in the presence of styrene as an activator, complex 1 is effective for the RCM of a sterically hindered diene.

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“…A study concerning the utilization of the molybdenum catalyst Sch-I proved that, under properly selected conditions, CM involving styrenes can lead to a variety of synthetically valuable building blocks. 30 Another class of easily dimerizing CM partners are allyl chlorides and bromides. The example of CM between allylbenzene, a type I olefin, and allyl bromide, promoted by Gru-I, was published by Castedo et al (Scheme 12).…”

Section: CMmentioning

confidence: 99%