Excellent Trans-selectivity Research Articles

Catalyst-Free Trans-Selective Oxyiodination and Oxychlorination of Alkynes Employing N-X (Halogen) Reagents.

β-halogenated enol esters and ethers are versatile building blocks in organic synthesis, which has attracted increasing attention. In this study, we report the facile trans-oxyiodination and oxychlorination of alkynes, leading to the direct construction of versatile halogenated enol esters and ethers. This transformation features an easy operation, optimal atomic economy, a strong functional group tolerance, broad substrate scope, and excellent trans-selectivity. Employing highly electrophilic bifunctional N-X (halogen) reagents was the key to achieving broad reaction generality. To our knowledge, this transformation represents the first oxyhalogenation system employing N-X (halogen) reagents as both oxylation and halogenation sources.

Photoinduced Bisphosphination of Alkynes with Phosphorus Interelement Compounds and Its Application to Double-Bond Isomerization.

The addition of interelement compounds with heteroatom-heteroatom single bonds to carbon-carbon unsaturated bonds under light irradiation is believed to be an atomically efficient method to procure materials with carbon-heteroatom bonds. In this study, we achieved the photoinduced bisphosphination of alkynes using the phosphorus interelement compound, tetraphenyldiphosphine monosulfide (1), to stereoselectively obtain the corresponding (E)-vic-1,2-bisphosphinoalkenes, which are important transition-metal ligands. The bisphosphination reaction was performed by mixing 1 and various alkynes and then exposing the mixture to light irradiation. Optimization of the conditions for the bisphosphination reaction resulted in a wide substrate range and excellent trans-selectivity. Moreover, the completely regioselective introduction of pentavalent and trivalent phosphorus groups to the terminal and internal positions of the alkynes, respectively, was achieved. We also found that the novel double-bond isomerization reaction of the synthesized bisphosphinated products occurred with a catalytic amount of a base under mild conditions. Our method for the photoinduced bisphosphination of carbon-carbon unsaturated compounds may have strong implications for both organic synthesis and organometallic and catalyst chemistry.

Nickel-catalyzed allylic carbonylative coupling of alkyl zinc reagents with tert-butyl isocyanide

Transition metal-catalyzed carbonylation with carbon nucleophiles is one of the most prominent methods to construct ketones, which are highly versatile motifs prevalent in a variety of organic compounds. In comparison to the well-established palladium catalytic system, the nickel-catalyzed carbonylative coupling is much underdeveloped due to the strong binding affinity of CO to nickel. By leveraging easily accessible tert-butyl isocyanide as the CO surrogate, we present a nickel-catalyzed allylic carbonylative coupling with alkyl zinc reagent, allowing for the practical and straightforward preparation of synthetically important β,γ-unsaturated ketones in a linear-selective fashion with excellent trans-selectivity under mild conditions. Moreover, the undesired polycarbonylation process which is often encountered in palladium chemistry could be completely suppressed. This nickel-based method features excellent functional group tolerance, even including the active aryl iodide functionality to allow the orthogonal derivatization of β,γ-unsaturated ketones. Preliminary mechanistic studies suggest that the reaction proceeds via a π-allylnickel intermediate.

Highly stereoselective cyclopropanation of various olefins with diazosulfones catalyzed by Ru(ii)-Pheox complexes.

A highly stereoselective cyclopropanation of various olefins with diazosulfones catalyzed by chiral Ru(ii)-Pheox complexes was developed to give chiral cyclopropyl sulfones in high yields (up to 99%) with excellent trans-selectivity and enantioselectivity (up to 98% ee).

Photoinduced metal-free diboration of alkynes in the presence of organophosphine catalysts

In sharp contrast to the transition metal-catalyzed diboration of alkynes with diboron species such as B2pin2, which affords vicinal cis-diborated alkenes, the organophosphine-catalyzed addition of B2pin2 to alkynes proceeds under metal-free conditions upon photoirradiation to give the corresponding vicinal trans-diborated alkenes with good stereoselectivity. For example, the photoinduced diboration of 1-octyne with B2pin2 in the presence of tris(o-methylphenyl)phosphine afforded 1,2-diborated octene with excellent trans selectivity (trans/cis=95/5). The influence of various organophosphines on the diboration is described in detail. The diboration does not occur in the dark or in the absence of an organophosphine catalyst. Moreover, ESR (electron spin resonance) measurements of the reaction mixture revealed a radical species around g=2.003, supporting a radical pathway for the organophosphine-catalyzed diboration. In addition, the photoinduced cis to trans isomerization of vicinal cis-diborated alkenes in the presence/absence of organophosphines is discussed.

Electrochemical intramolecular aminooxygenation of unactivated alkenes.

An electrochemical approach to the intramolecular aminooxygenation of unactivated alkenes has been developed. This process is based on the addition of nitrogen-centered radicals, generated through electrochemical oxidation, to alkenes followed by trapping of the cyclized radical intermediate with 2,2,6,6-tetramethylpiperidine-N-oxyl radical (TEMPO). Difunctionalization of a variety of alkenes with easily available carbamates/amides and TEMPO affords aminooxygenation products in high yields and with excellent trans selectivity for cyclic systems (d.r. up to>20:1). The approach provides a much-needed complementary route to existing cis-selective methods.

Synthesis of the Tetrahydropyran Fragment of Bistramide D

AbstractA synthesis of the tetrahydropyran (THP) moiety of bistramide D has been completed by using cross‐metathesis and kinetically controlled intramolecular oxa‐Michael addition to form the ring with excellent trans selectivity. The C9 methyl substituent was introduced by using an unsaturated sulfone building block, which can be most effectively prepared through a combination of diastereoselective allylation and alkene isomerisation. The effect of this methyl group on subsequent cross‐metathesis reactions can be mitigated by careful choice of reaction conditions.

Ruthenium‐Catalyzed trans‐Selective Hydrostannation of Alkynes

In contrast to all other transition-metal-catalyzed hydrostannation reactions documented in the literature, the addition of Bu3SnH across various types of alkynes proceeds with excellent trans selectivity, provided the reaction is catalyzed by [Cp*Ru]-based complexes. This method is distinguished by a broad substrate scope and a remarkable compatibility with functional groups, including various substituents that would neither survive under the conditions of established Lewis acid mediated trans hydrostannations nor withstand free-radical reactions. In case of unsymmetrical alkynes, a cooperative effect between the proper catalyst and protic functionality in the substrate allows outstanding levels of regioselectivity to be secured as well.

Ruthenium‐Catalyzed trans‐Selective Hydrostannation of Alkynes

AbstractIn contrast to all other transition‐metal‐catalyzed hydrostannation reactions documented in the literature, the addition of Bu3SnH across various types of alkynes proceeds with excellent trans selectivity, provided the reaction is catalyzed by [Cp*Ru]‐based complexes. This method is distinguished by a broad substrate scope and a remarkable compatibility with functional groups, including various substituents that would neither survive under the conditions of established Lewis acid mediated trans hydrostannations nor withstand free‐radical reactions. In case of unsymmetrical alkynes, a cooperative effect between the proper catalyst and protic functionality in the substrate allows outstanding levels of regioselectivity to be secured as well.

Novel iodine catalyzed diastereoselective synthesis of trans-2,6-disubstituted tetrahydro-2H-pyrans: synthesis of C1–C13 fragment of bistramide-A

A new method for the stereoselective synthesis of trans 2.6-disubstituted tetrahydro-2H-pyrans has been developed involving iodine catalyzed allylation of tetrahydro-2H-pyranol with excellent trans selectivity. The method was also applied toward the construction of C1–C13 fragment of bistramide-A in 11 steps with 21.4% overall yield.

ChemInform Abstract: Nucleophilic Carbene‐Catalyzed Redox‐Esterification Reaction of α‐Halo‐α,β‐unsaturated Aldehydes.

AbstractThe NHC‐catalyzed redox‐esterification of α‐halo‐α,β‐unsaturated aldehydes provides unsaturated esters with high yields and excellent trans selectivity.

Nucleophilic carbene-catalyzed redox-esterification reaction of α-halo-α,β-unsaturated aldehyde

A nucleophilic carbene catalyzed redox esterification between α-halo-α,β-unsaturated aldehydes and various alcohols has been developed. Interestingly, the reaction provided α,β-unsaturated esters instead of the saturated α-halo substituted esters as the only product in good to high yield with excellent trans-selectivity, presumably via the umpolung-halo-elimination pathway.

Syntheses of Resveratrol and its Hydroxylated Derivatives as Radical Scavenger and Tyrosinase Inhibitor

Eight hydroxylated stilbene derivatives including resveratrol, desoxyrhapontigenin and piceatannol as potential radical scavenger and tyrosinase inhibitor are synthesized using optimized Wittig-Horner reaction for excellent trans-selectivity in good yields. Antioxidant activity was tested against ABTS radical and tyrosinase inhibitory activity was performed with L-tyrosine as the substrate based on previous procedure with some modification. In general, catecholic stilbenes showed stronger activity against ABTS radical and resorcinolic moiety showed stronger tyrosinase inhibitory activity. Synthetic piceatannol which containing both catecholic and resorcinolic moieties showed the strongest activity in both as ABTS radical scavenger and tyrosinase inhibitor with IC

Synthesis of 4-Iodopiperidines via Aza-Prins Cyclization

Presented here is a one-step, three-component synthesis of 2-mono- and 2,6-disubstituted 4-iodopiperidines from homoallylic amines and aldehydes via aza-Prins cyclization using a catalytic amount of gallium(III) iodide and stoichiometric iodine. Excellent trans selectivity was observed for the formation of 2,4-disubstituted piperidines. Substituted homoallylic amines afforded 2,4,6-trisubstituted piperidines with all cis configuration. Other metal iodides (In, Al, Mg) with iodine (1 equiv) gave slightly lower yields. Catalytic FeCl3 (10 mol%) with iodine (1 equiv) gave 4-iodopiperidines along with 4-chloropiperidine products.

A catalytic and stoichiometric approach to the synthesis of the steroid B-ring en route to estratrienes

Zirconocene catalyzed cyclization of 2-(5-methoxy-3-penten-1-yl)styrene in the presence of organomagnesium reagents was studied. The cyclization proceeded in high isolated yields (up to 84%) with excellent trans-selectivity (>98%), which is unusual for the formation of cyclohexane derivatives. Catalytic cyclization in the presence of Cp 2ZrCl 2 proceeded as well with similar results. The reaction with ( R, R)-(EBTHI) 2ZrCl 2 gave a cis/trans mixture of 5 in low yield and poor ee.

A straightforward approach towards cyclic peptides via ring-closing metathesis—scope and limitations

N- and C-terminal diallylated peptides are obtained by several approaches, such as peptide Claisen rearrangement, N- and O- allylation, and the Ugi reaction of allyl-protected components. These diallylated peptides are suitable substrates for ring-closing metathesis and the success of this cyclisation was investigated with respect to the ring size, the position of the allyl moieties and the reaction parameters. In general, excellent yields are obtained for cyclisation of allyl glycine subunits and N-allylated amides, while allyl esters and allyl carbamates often presented serious problems. However, yields of up to 73% were obtained under optimised conditions, and the new generated double bond is formed with excellent trans-selectivity.

Improved One‐Pot Synthesis of Styryl Tetrahydrofurans and Cyclohexanes by Radical Addition to β‐Nitrostyrenes in the Presence of Benzoyl Peroxide.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Improved one-pot synthesis of styryl tetrahydrofurans and cyclohexanes by radical addition to beta-nitrostyrenes in the presence of benzoyl peroxide.

Stereoselective styryl derivatives have been prepared based on radical substitution (addition-elimination) of heterocycles or cyclohydrocarbons units to (E)-beta-nitrostyrenes 1 using a common radical initiator benzoyl peroxide. High reactivity and selectivity with wide substrate scope were attained by using this easy methodology. The reactions using easily obtained and one-pot potential starting materials gave excellent trans-selectivity with medium to high yields in all cases. Synthetic utility of this approach has been demonstrated by the preparation of various trans-styryl derivatives.

A Polymer-supported Iridium Catalyst for the Stereoselective Isomerisation of Double Bonds

A polymer-supported iridium catalyst has been prepared and used in the isomerisation of the double bonds in aryl allylic derivatives with excellent trans selectivity and without the need for conventional work-up procedures.

Cyclization/Hydrosilylation of Functionalized Dienes Catalyzed by a Cationic Palladium Phenanthroline Complex

Mixtures of (phen)PdMe2 (2a) and HBAr‘4 (3a) or (phen)PdMe(Cl) (2b) and NaBAr‘4 (3b) [phen = 1,10-phenanthroline; Ar‘ = 3,5-C6H3(CF3)2] catalyzed the cyclization/hydrosilylation of functionalized 1,6-dienes to form silylated cyclopentanes in good yield and with excellent trans selectivity about the newly formed C−C bond (typically >50:1). A range of tertiary hydrosilanes were employed in the procedure although unhindered trialkylsilanes provided the most consistent results. The protocol tolerated a range of polar functionality including esters, ethers, amides, sulfones, and cyano groups. 4,4-Disubstitution on the diene backbone promoted cyclization, and a homoallylic ester, ketone, or ether directing group was required for efficient cyclization. The procedure tolerated dienes which possessed a single trans-substituted olefin and also tolerated allylic substitution. These substituted dienes underwent cyclization/hydrosilylation to form carbocycles resulting from transfer of the silyl group to the less hind...