Rhenium-catalyzed regiodivergent addition of indoles to terminal alkynes

An efficient rhenium-catalyzed site-switchable addition of indoles to terminal alkynes is described. A variety of bisindolylalkane derivatives are expeditiously synthesized in high yields with excellent regioselectivity. Preliminary mechanistic study sheds light on the observed regiodivergent addition.     

Pt-catalyzed regio- and stereoselective pyridylthiolation of terminal alkynes

Three-component cross-coupling reactions among 3-iodopyridynes, terminal alkynes and ArSK took place in the presence of Pt-catalyst to give pyridine derivatives with conjugated vinyl groups in moderate yields.     

Base-mediated regio- and stereoselective intermolecular addition of alkynes to N-heterocycles

The regio- and stereoselective addition of N-heterocycles to alkynes using KOH is reported. Formation of (Z)-isomers and their conversion to (E)-products were found to be dependent upon time as well as the choice of base. Selective attack of N-heterocycles on a more electrophilic alkynyl carbon was supported by DFT calculations, and the stereochemistry of the products was established by X-ray crystallographic studies and intramolecular cyclization of ortho-haloalkynes in indolo-[2,1-a]isoquinolines.     

Iron-catalyzed regio- and stereoselective chlorosulfonylation of terminal alkynes with aromatic sulfonyl chlorides

Terminal alkynes react with aromatic sulfonyl chlorides in the presence of an iron(II) catalyst and a phosphine ligand to give (E)-β-chlorovinylsulfones with 100% regio- and stereoselectivity. Various functional groups, such as chloride, bromide, iodide, nitro, ketone, and aldehyde, are tolerated under the reaction conditions. Addition of tosyl chloride to a 1,6-enyne followed by radical 5-exo-trig cyclization gave an exocyclic alkenylsulfone.     

Rhodium-catalyzed regio- and stereoselective codimerization of alkenes and electron-deficient internal alkynes leading to 1,3-dienes

A cationic rhodium(I)/H(8)-BINAP complex catalyzes codimerization of alkenes bearing no alpha-hydrogen and electron-deficient internal alkynes, leading to 1,3-dienes in good yields with moderate to excellent regio- and stereoselectivity. The same complex also catalyzes codimerization of an acrylate and phenyl-substituted electron-rich internal alkynes, leading to 1,3-dienes.     

Platinum-catalyzed regio- and stereoselective arylthiolation of internal alkynes

Unsymmetrical internal alkynes such as ethyl phenylpropiolate (2b) successfully underwent Pt-catalyzed decarbonylative arylthiolation by thioesters. The regio- and stereoselective insertion of 2b into an S-Pt bond was confirmed by reaction with a platinum complex with an S-Pt-Cl framework.     

Palladium-catalyzed regio- and stereoselective hydrosilylation of electron-deficient alkynes

Highly regio- and stereoselective hydrosilylation applicable to a broad range of electron-deficient alkynes has been established using palladium catalysis. The synthetic utility of the method has been demonstrated by further transformations of α-silylalkenes, particularly Hiyama coupling and stereoinverting iododesilylation followed by Suzuki-Miyaura coupling, which enables stereodivergent syntheses of α-arylenoates.     

Ruthenium-catalyzed regio- and stereoselective addition of carboxylic acids to aryl and trifluoromethyl group substituted unsymmetrical internal alkynes

The regio- and stereoselective addition of carboxylic acids to aryl and trifluoromethyl group substituted unsymmetrical internal alkynes has been accomplished: the Ru(3)(CO)(12)/3PPh(3) catalyst system has effectively catalyzed the reaction to afford the trifluoromethyl group substituted (E)-enol esters with high regio- and stereoselectivities.     

ZnCl2-mediated stereoselective addition of terminal alkynes to D-(+)-mannofuranosyl nitrones

[reaction: see text] An optimized process for the addition of terminal alkynes to chiral nitrones using ZnCl2 and NEt3 in toluene is reported. The new reaction protocol is facile to perform and cost-effective. The resulting optically active propargyl N-hydroxylamines are isolated in good to excellent yield and high diastereoselectivity.     

Ru-catalyzed stereoselective addition of imides to alkynes

A catalyst system formed in situ from bis(2-methylallyl)cycloocta-1,5-dieneruthenium(II) ((cod)Ru[met]2), a phosphine, and scandium(III) trifluoromethanesulfonate (Sc(OTf)3) was found to efficiently catalyze the anti-Markovnikov addition of imides to terminal alkynes, allowing mild and atom-economic synthesis of enimides. Depending on the phosphine employed, both the (E)- and the (Z)-isomer can be accessed stereoselectively.     

N-heterocyclic carbene-catalyzed regio- and stereoselective hydrothiolation reaction of alkynes

N-heterocyclic carbenes (NHCs) have been utilized as Brønsted base to catalyze the hydrothiolation reaction between alkynes and thiols to produce the vinyl sulfides stereoselectively.     

Regio- and stereoselective hydrosilylation of immobilized terminal alkynes

Regio- and stereoselective hydrosilylation of terminal alkynes on solid support using diisopropyl hydrosilanes yielding β-(E)-vinyl silanes with excellent selectivity is reported. The hydrosilylation is catalyzed by Pt(DVDS)/P(ⁱBuNCH₂CH₂)₃N (DVDS = 1,3-divinyl-1,1,3,3-tetramethyl-disiloxane), in which the bulky proazaphosphatrane ligand plays a key role for the selectivity. The immobilized products are characterized with gel phase¹³C NMR and ¹H high resolution magic angle spinning NMR.     

Diastereoselective alkynylation of glucose-modified imines with terminal alkynes

The copper(I)-catalyzed enantioselective alkynylation of aldimines incorporating a 2,3,4,6-tetrakis-O-pivaloyl-d-glucopyranosyl (Piv₄Glc) chiral auxiliary with terminal alkynes is reported. The present system provides a versatile tool for the construction of optically active propargylamine derivatives. Good yields and enantiomeric excess values were achieved with an array of imines and biologically active, propargylamine derivatives.     

Highly stereoselective one-pot procedure to prepare bis- and tris-chalcogenide alkenes via addition of disulfides and diselenides to terminal alkynes

We present here the reaction of diorganoyl dichalcogenides with terminal alkynes under catalyst-free conditions, by a one-pot procedure, to prepare bis- and tris-chalcogenide alkenes selectively, avoiding the previous preparation of chalcogen alkynes. The reaction proceeded cleanly under mild reaction conditions, and the addition of dichalcogenides to alkynes occurred stereoselectively to give exclusively the corresponding Z isomers. We observed that the selectivity control was governed by the effective participation of the hydroxyl group from propargyl alcohols. In addition, the bis-chalcogenide alkenes were exclusively obtained with propargyl alcohol having the acidic hydroxyl group proton. Conversely, the alkynes with no potentially acidic hydroxyl group proton, at propargyl positions, gave exclusively the tris-chalcogenide alkenes.     

Allylcyanation of alkynes: regio- and stereoselective access to functionalized di- or trisubstituted acrylonitriles

Allyl cyanides are found to add across alkynes in the presence of a nickel catalyst prepared from Ni(cod)2 and P(4-CF3-C6H4)3 in situ to give variously functionalized di- or trisubstituted acrylonitriles in highly stereoselective manners possibly via a pi-allylnickel species as an intermediate. alpha-Siloxyallyl cyanides also react at the gamma-position of a cyano group with both internal and terminal alkynes having various functional groups to give silyl enol ethers, which give the corresponding aldehydes or ketones upon hydrolysis.     

Palladium-catalyzed conjugate addition of terminal alkynes to enones

A practical protocol for the hydroalkynylation of enones using Pd catalysis is reported. The reaction proceeds efficiently with a variety of alkynes as well as with several cyclic and acyclic enones, providing synthetically relevant β-alkynyl ketones in good to excellent yields.     

Rhenium-catalyzed hydroamidation of unactivated terminal alkynes: synthesis of (E)-enamides

Reactions of cyclic amides with unactivated terminal alkynes in the presence of a catalytic amount of a rhenium complex provided (E)-enamides in high regio- and stereoselectivity (E:Z = >99:<1).