Abstract:We report a Rh-catalyzed hydrothiolation of 1,3-dienes, including petroleum feedstocks. Either secondary or tertiary allylic sulfides can be generated from the selective addition of a thiol to the more substituted double bond of a diene. The catalyst tolerates a wide range of functional groups, and the loading can be as low as 0.1 mol %.
“…2, entry 10). Interestingly, after a thorough re-evaluation of the reaction parameters, we were able to change the thiolation site to the terminal position 54–60 to generate a very good yield of the linear thioether as a single isomer (Fig. 2, entry 11).Fig.…”
Section: Resultsmentioning
confidence: 98%
“…2 and Fig. 10b, the current benzylic regioselectivity can also be switched to a terminal site to form the anti -Markovnikov hydrothiolation 54–60 products. A series of terminal alkenes can be effectively hydrothiolated under a modified reaction conditions ( 8a – 8d ).…”
Direct (utilize easily available and abundant precursors) and selective (both chemo- and regio-) aliphatic C–H functionalization is an attractive mean with which to streamline chemical synthesis. With many possible sites of reaction, traditional methods often need an adjacent polar directing group nearby to achieve high regio- and chemoselectivity and are often restricted to a single site of functionalization. Here we report a remote aliphatic C–H thiolation process with predictable and switchable regioselectivity through NiH-catalysed migratory hydrothiolation of two feedstock chemicals (alkenes/alkynes and thiols). This mild reaction avoids the preparation of electrophilic thiolation reagents and is highly selective to thiols over other nucleophilic groups, such as alcohols, acids, amines, and amides. Mechanistic studies show that the reaction occurs through the formation of an RS-Bpin intermediate, and THF as the solvent plays an important role in the regeneration of NiH species.
“…2, entry 10). Interestingly, after a thorough re-evaluation of the reaction parameters, we were able to change the thiolation site to the terminal position 54–60 to generate a very good yield of the linear thioether as a single isomer (Fig. 2, entry 11).Fig.…”
Section: Resultsmentioning
confidence: 98%
“…2 and Fig. 10b, the current benzylic regioselectivity can also be switched to a terminal site to form the anti -Markovnikov hydrothiolation 54–60 products. A series of terminal alkenes can be effectively hydrothiolated under a modified reaction conditions ( 8a – 8d ).…”
Direct (utilize easily available and abundant precursors) and selective (both chemo- and regio-) aliphatic C–H functionalization is an attractive mean with which to streamline chemical synthesis. With many possible sites of reaction, traditional methods often need an adjacent polar directing group nearby to achieve high regio- and chemoselectivity and are often restricted to a single site of functionalization. Here we report a remote aliphatic C–H thiolation process with predictable and switchable regioselectivity through NiH-catalysed migratory hydrothiolation of two feedstock chemicals (alkenes/alkynes and thiols). This mild reaction avoids the preparation of electrophilic thiolation reagents and is highly selective to thiols over other nucleophilic groups, such as alcohols, acids, amines, and amides. Mechanistic studies show that the reaction occurs through the formation of an RS-Bpin intermediate, and THF as the solvent plays an important role in the regeneration of NiH species.
“…Encouraged by this result and given the vital role of ligands in transition metal catalyzed transformations,w en ext interrogated as eries of commercially available ligands to improve the reaction efficiency.N otably,a8 5% yield of the desired product was obtained when the bidentate and electron-rich phosphine ligand dmpe [1,2-bis(dimethylphosphino)ethane]w as used (entry 4), while the other phosphine-, nitrogen-containing and/or N-heterocyclic carbene (NHC) ligands were found to be inferior for this transformation, leaving most of the starting 1,3-diene unreacted (entries 2-12). Further investigation of several common ruthenium(II) catalysts showed that comparative selectivity and yields could be achieved (entries [13][14][15]. Al ook at the bases revealed that t BuOLi gave the best results (entries [16][17][18][19].…”
Section: Resultsmentioning
confidence: 99%
“…[12] In other words,a tl east six different regioisomers can be potentially formed during the addition of NuÀHacross aterminal diene,and the selectivity of the newly formed bonds depends on either the Markovnikov or anti-Markovnikov selectivity for internal addition, terminal 1,2addition, or conjugate 1,4-addition (Scheme 1a). [13][14][15][16] Recently our group [17] and that of Zhou [18] independently communicated an ickel-catalyzed 1,2-Markovnikov hydroalkylation [19] of 1,3-dienes with umpolung carbonyls to generate branched allylic compounds (Scheme 1b). In these reactions,anickel hydride species is generated and reacts with the diene to generate an electrophilic nickel-p-allyl intermediate (hydride adds preferentially to the less sterically hindered terminal olefinic carbon center;S cheme 1c,l eft).…”
Controlling reaction selectivity is a permanent pursuit for chemists. Regioselective catalysis, which exploits and/or overcomes innate steric and electronic bias to deliver diverse regio‐enriched products from the same starting materials, represents a powerful tool for divergent synthesis. Recently, the 1,2‐Markovnikov hydroalkylation of 1,3‐dienes with simple hydrazones was reported to generate branched allylic compounds when a nickel catalyst was used. As part of the effort, shown here is that a complete switch of Markovnikov to anti‐Markovnikov addition is obtained by changing to a ruthenium catalyst, thus providing direct and efficient access to homoallylic products exclusively. Isotopic substitution experiments indicate that no reversible hydro‐metallation across the metal‐π‐allyl system occurred under ruthenium catalysis. Moreover, this protocol is applicable to the regiospecific hydroalkylation of the distal C=C bond of 1,3‐enynes.
“…. ) are very often applied as catalyst precursors in homogeneous catalysis [24][25][26][27][28][29][30][31][32][33][34][35][36][37]. These coordination compounds are usually not commercially available and must therefore be synthesized.…”
Section: In Situ Generation Of Precatalystsmentioning
In the present work, the rich chemistry of rhodium/phosphine complexes, which are applied as homogeneous catalysts to promote a wide range of chemical transformations, has been used to showcase how the in situ generation of precatalysts, the conversion of precatalysts into the actually active species, as well as the reaction of the catalyst itself with other components in the reaction medium (substrates, solvents, additives) can lead to a number of deactivation phenomena and thus impact the efficiency of a catalytic process. Such phenomena may go unnoticed or may be overlooked, thus preventing the full understanding of the catalytic process which is a prerequisite for its optimization. Based on recent findings both from others and the authors’ laboratory concerning the chemistry of rhodium/diphosphine complexes, some guidelines are provided for the optimal generation of the catalytic active species from a suitable rhodium precursor and the diphosphine of interest; for the choice of the best solvent to prevent aggregation of coordinatively unsaturated metal fragments and sequestration of the active metal through too strong metal–solvent interactions; for preventing catalyst poisoning due to irreversible reaction with the product of the catalytic process or impurities present in the substrate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
