Highly Regioselective Hydrosilylation of Unsymmetric Alkynes Using a Phenylthio Directing Group

Huang, Kuan‐Hsun; Isobe, Mitsuaki

doi:10.1002/ejoc.201402577

“…[2] However,d espite the significant progress made,t here still remain challenges (e.g.,r egio-and stereocontrol), particularly for unsymmetrical internal alkynes in intermolecular reactions (Scheme 1). [5] In continuation of our studies on transformations of electron-rich alkynes, [6] we report herein the first general, mild, and highly selective process of this type (Scheme 1b). In contrast, the hydrosilylation of electron-rich alkynes (bearing an electron-donating group (EDG) at the triple bond) remains largely unknown.…”

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confidence: 81%

“…[8] Theu se of other solvents did not improve the overall efficiencyand selectivity of the reaction. [5] We next examined ar ange of silanes ( Table 2). Furthermore,p reviously reported Pt and Co complexes were found to be ineffective (Table 1, entries 3a nd 4).…”

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confidence: 99%

Highly Regio‐ and Stereoselective Hydrosilylation of Internal Thioalkynes under Mild Conditions

Ding

¹

,

Song

²

,

Wang

³

et al. 2015

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A general and mild hydrosilylation of thioalkynes is described. With the cationic catalyst [Cp*Ru(MeCN)3 ](+) and the bulky silane (TMSO)3 SiH, a range of thioalkynes underwent smooth hydrosilylation at room temperature with excellent α regioselectivity and syn stereoselectivity. DFT calculations provided important insight into the mechanism, particularly the unusual syn selectivity with the [Cp*Ru(MeCN)3 ](+) catalyst. The sulfenyl group in the substrates was found to provide important chelation stabilization to direct the reaction through a new mechanistic pathway.

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“…

Non-oxidative,regioselective,and convergent access to densely functionalized oxazoles is realized in af unctionalgroup tolerant manner using alkynyl thioethers.S ulfur-terminated alkynes provideaccess to reactivity previously requiring strong donor-substituted alkynes such as ynamides.Sulfur does not act in an analogous donor fashion in this gold-catalyzed reaction, thus leading to complementary regioselective outcomes and addressing the limitations of using ynamides.Compared to other heteroatom-substituted alkynes,alkynyl thioethers are remarkably little explored in intermolecular late-transition-metal catalysis,d espite being readily accessed and robust. [1,2] Ynamides,i nc ontrast, are privileged substrates:i np-acid catalysis their donor nature aids metalalkyne coordination and affords highly polarized electrophiles,t hus providing the high chemo-and regioselectivity required for the discovery of efficient intermolecular reactions (Scheme 1a). [3,4] As the resulting inclusion of ad onornitrogen atom limits the utility of the products,r etaining the reactivity profile of these transformations whilst accessing more flexible and readily elaborated substitution patterns would be desirable.T he value of sulfur-substituted compounds [5] coupled with progress in C À Ca nd C-heteroatom bond formation from CÀSbonds, [6] renders alkynyl thioethers appealing alternatives to ynamides.I ndeed the ketenethionium pathway (Scheme 1a)f rom alkynyl thioethers has recently been invoked in proton-catalyzed reactions with nitriles [2g,h] and gold-catalyzed reactions with sulfides.

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confidence: 99%

Alkynyl Thioethers in Gold‐Catalyzed Annulations To Form Oxazoles

Reddy

¹

,

Ball‐Jones

²

,

Davies

³

2017

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Non-oxidative,regioselective,and convergent access to densely functionalized oxazoles is realized in af unctionalgroup tolerant manner using alkynyl thioethers.S ulfur-terminated alkynes provideaccess to reactivity previously requiring strong donor-substituted alkynes such as ynamides.Sulfur does not act in an analogous donor fashion in this gold-catalyzed reaction, thus leading to complementary regioselective outcomes and addressing the limitations of using ynamides.Compared to other heteroatom-substituted alkynes,alkynyl thioethers are remarkably little explored in intermolecular late-transition-metal catalysis,d espite being readily accessed and robust. [1,2] Ynamides,i nc ontrast, are privileged substrates:i np-acid catalysis their donor nature aids metalalkyne coordination and affords highly polarized electrophiles,t hus providing the high chemo-and regioselectivity required for the discovery of efficient intermolecular reactions (Scheme 1a). [3,4] As the resulting inclusion of ad onornitrogen atom limits the utility of the products,r etaining the reactivity profile of these transformations whilst accessing more flexible and readily elaborated substitution patterns would be desirable.T he value of sulfur-substituted compounds [5] coupled with progress in C À Ca nd C-heteroatom bond formation from CÀSbonds, [6] renders alkynyl thioethers appealing alternatives to ynamides.I ndeed the ketenethionium pathway (Scheme 1a)f rom alkynyl thioethers has recently been invoked in proton-catalyzed reactions with nitriles [2g,h] and gold-catalyzed reactions with sulfides.[2i]Ynamides enabled the discovery of formal [3+ +2] dipolar cycloadditions with nucleophilic nitrenoids, [7] thus allowing intermolecular access to a-imino gold carbene-type reactivity for heterocycle synthesis (Scheme 1b). [8, 9] Such reactions, which do not depend on ynamides,a re scarce.[8b,h] As trong donor alkyne substituent proved critical in the formation of oxazoles using N-acyl pyridinium N-aminides,aselectron-rich alkynes such as anisole derivatives did not react (Scheme 1b, inset). [8a,b] Oxazoles are valuable synthetic intermediates [10,11] and structural components in bioactive natural products, [12] agrochemicals, [13] ligands, [14] and functional materials.[15]Despite recent advances,asingle modular and convergent route to trisubstituted oxazoles,which provides the structural and functional-group diversity needed across the 2-, 4-, and 5-positions,r emains unrealized. [16] Following our interest in the use of gold catalysis with sulfides [17] we report here on the reactivity of alkynyl thioethers with nucleophilic nitrenoids to prepare oxazoles. Importantly,t he regioselectivity is not consistent with ac ontrolling ketenethionium species.T he sulfur group plays an alternative role in enabling reactivity,t hus proving complementary to donor-enabled approaches.Ther eaction of the alkynyl thioether 1a and aminide 2a (Table 1) showed that conversion into the oxazole 3 was possible at 125 8 8Ci n1 ,2-dichlorobenzene (1,2-DCB;s ee...

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“…In contrast, the hydrosilylation of electron-rich alkynes (bearing an electron-donating group (EDG) at the triple bond) remains largely unknown. [5] In continuation of our studies on transformations of electron-rich alkynes, [6] we report herein the first general, mild, and highly selective process of this type (Scheme 1b). Specifically,w eh ave developed an efficient rutheniumcatalyzed intermolecular hydrosilylation of internal thioalkynes with high regio-and stereoselectivity.I nt his study, we also observed unprecedented syn addition selectivity with [Cp*Ru(MeCN) 3 ] + (Cp* = pentamethylcyclopentadienyl), awell-known catalyst for anti addition reactions of alkynes.…”

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confidence: 81%

“…Furthermore,p reviously reported Pt and Co complexes were found to be ineffective ( Table 1, entries 3a nd 4). [5] We next examined ar ange of silanes ( Table 2). Most of them gave the product either in moderate yield or with moderate selectivity;h owever,t ris(trimethylsiloxy)silane (2h)provided the product in quantitative yield with excellent selectivity ( Table 2, entry 7).…”

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confidence: 99%