Complete Trans Selectivity Research Articles

AuI-Catalyzed Hydroalkynylation of Haloalkynes.

The AuI-catalyzed reaction between terminal alkynes and aromatic haloalkynes proceeds through divergent pathways depending on the nature of the catalyst counteranion. Thus, cationic complexes containing strongly basic NHC ligands and noncoordinating anions such as BArF4 catalyze the cis haloalkynylation of the terminal alkyne, whereas introduction of a weakly basic triflate counteranion results in the stereoselective hydroalkynylation of the haloalkyne, yielding haloenyne products in good yields and complete trans selectivity. Experimental and computational studies suggest that the hydroalkynylation reaction takes place via nucleophilic attack of the terminal alkyne to the C2 carbon of the activated haloalkyne, assisted by a concerted proton abstraction by the triflate, and that the protodeauration is the turnover-limiting step, in agreement with an observed primary kinetic isotope effect.

Redox-Neutral Rh(III)-Catalyzed Olefination of Carboxamides with Trifluoromethyl Allylic Carbonate.

The rhodium(III)-catalyzed olefination of various carboxamides with α-CF3-substituted allylic carbonate is described. This reaction provides direct access to linear CF3-allyl frameworks with complete trans-selectivity. In particular, a rhodium catalyst provided Heck-type γ-CF3-allylation products via the β-O-elimination of rhodacycle intermediate and subsequent olefin migration process.

ChemInform Abstract: Trifluoromethylallylation of Heterocyclic C—H Bonds with Allylic Carbonates under Rhodium Catalysis.

The rhodium(III)-catalyzed γ-trifluoromethylallylation of various heterocyclic C–H bonds with CF3-substituted allylic carbonates is described. These reactions provide direct access to linear CF3-containing allyl frameworks with complete trans-selectivity via C–H bond activation followed by a formal SN-type reaction pathway.

Trifluoromethylallylation of Heterocyclic C-H Bonds with Allylic Carbonates under Rhodium Catalysis.

The rhodium(III)-catalyzed γ-trifluoromethylallylation of various heterocyclic C-H bonds with CF3-substituted allylic carbonates is described. These reactions provide direct access to linear CF3-containing allyl frameworks with complete trans-selectivity via C-H bond activation followed by a formal SN-type reaction pathway.

ChemInform Abstract: A Total Synthesis of (+)‐Negamycin Through Isoxazolidine Allylation.

The β-amino acid antibiotic (+)-negamycin has been synthesised in ten steps from epichlorohydrin via Sakurai allylation of an isoxazolidine intermediate. The key allylation reaction proceeded with complete trans-selectivity, which is attributed to electrostatic attraction between the chlorine atom and the iminium ion in the Sakurai intermediate.

A total synthesis of (+)-negamycin through isoxazolidine allylation.

The β-amino acid antibiotic (+)-negamycin has been synthesised in ten steps from epichlorohydrin via Sakurai allylation of an isoxazolidine intermediate. The key allylation reaction proceeded with complete trans-selectivity, which is attributed to electrostatic attraction between the chlorine atom and the iminium ion in the Sakurai intermediate.

ChemInform Abstract: Tandem Synthesis of 2,3‐Dihydro‐4‐iminoquinolines via Three‐Component Alkyne‐Imine Metathesis.

AbstractThe reaction proceeds with complete trans selectivity in the absence of aryl catalyst.

Stereoselective Control of Planar α-Dimethylsulfonium Benzyl Carbanions. Synthesis of Optically Pure trans-Aziridines

(R)-N-sulfinylimine and (S)-N-sulfinylimine react with the ylide derived from (S)-dimethyl-[2-(p-toluenesulfinyl)phenyl]sulfonium salt, affording trans-2,3-disubstituted aziridines. A complete trans selectivity in low facial diastereoselectivity is observed when the configuration at the sulfur atoms of the reagents is the same. Otherwise, when their configurations are different, the reaction evolved with total facial diastereoselectivity and the cis/trans ratio ranged between 1/4.2 and 1/9. Theoretical calculations indicate the reaction proceeds mainly by evolution of a planar free carbanion. The relative stability of the transition states predicts a trans/cis ratio that is in excellent agreement with the experimental results.

Highly Stereoselective Radical Carbonylations of gem-Dihalocyclopropane Derivatives with CO

A couple of radical carbonylations of gem-dihalocyclopropanes 1 using CO and Bu3SnH (formylation) or Bu3Sn(CH2CH=CH2) (allylacylation) successfully proceeded to give trans and cis adducts (2 and 3) with good to excellent stereoselectivity (trans/cis = >99/1-75/25 or 17/83-1/99). The formylation of 2,3-cis-disubstituted 1,1-dihalocyclopropanes enhanced trans selectivity (trans/cis = >99/1-95/5), whereas both 2,3-cis-disubstituted and 2-monosubstituted 1,1-dihalocyclopropanes underwent allylacylation with nearly complete trans selectivity (trans/cis = >99/1). Inherently less reactive gem-dichloro- and bromochlorocyclopropanes than gem-dibromocyclopropanes served as favorable substrates. [reaction: see text].

Regioselective cis,vic-Dihydroxylation of α,β,γ,δ-Unsaturated Carboxylic Esters: Enhanced γ,δ-Selectivity by Employing Trifluoroethyl or Hexafluoroisopropyl Esters

The regioselectivity of Sharpless asymmetric dihydroxylation (AD) of α,β,γ,δ-unsaturated carboxylic esters was studied as a function of α-, β-, and δ-substituents and for fluorine-free versus fluorinated esters. The latter showed increased or complete γ,δ-selectivities: the hexafluoroisopropyl ester being superior to the tri­fluoroethyl ester. Olefinations of α,β-unsaturated aldehydes with phosphorus ylide 36 or phosphonate anion 41 provided α,β,γ,δ-unsaturated trifluoroethyl esters, leading inter alia to complete trans selectivity and to 31 with 94% E selectivity, respectively.

Synthesis of Epoxides from Aldehydes and Tosylhydrazone Salts Catalyzed by Triphenylarsine: Complete trans Selectivity for all Combinations of Coupling Partners.

Synthesis of Epoxides from Aldehydes and Tosylhydrazone Salts Catalyzed by Triphenylarsine: Complete trans Selectivity for all Combinations of Coupling Partners.

Synthesis of epoxides from aldehydes and tosylhydrazone salts catalysed by triphenylarsine: complete trans selectivity for all combinations of coupling partners.

Triphenylarsine catalyses the formation of epoxides from carbonyl compounds and tosylhydrazone salts. This convergent synthesis gives complete trans selectivity for all aldehyde and tosylhydrazone salt coupling partners.

Addition of chiral enolates to N-alkyl-3-acylpyridinium salts. Total synthesis of (+)-16-epivinoxine and (−)-vinoxine

Chiral enolates of indolylacetyl derivatives 6a– f undergo addition to pyridinium salt 7 with complete trans-selectivity and varied diastereofacial selectivities to give, after acid-induced cyclization of the intermediate 1,4-dihydropyridines, the vinoxine-related tetracycles 8a– f. Starting from ( S)-prolinol indolylacetamide 6e, subsequent elaboration of the ethylidene substituent from tetracycle 8e and removal of the chiral auxiliary has resulted in a straightforward synthesis of (+)-16-epivinoxine and (−)-vinoxine.

Synthesis of Enantiomerically Pure Aziridine-2-imides by Cyclization of Chiral 3‘-Benzyloxyamino Imide Enolates

Aziridine-2-imides are prepared both in high yield and high diastereoselectivity from chiral 3‘-benzyloxyamino imides 2, 3, and 8 by treatment with triethylamine in the presence of either TiCl4 or AlMe2Cl. 2 and 3 are easily obtained by a diastereoselective conjugate addition of O-benzylhydroxylamine promoted by Lewis acids to α,β-unsaturated imides 1. The synthesis of 3‘-(benzyloxyamino)propanoyl 8 is performed by addition to the acryloyl compound 6 of N-BOC O-benzylhydroxylamine followed by deprotection. The cyclization of 2 and 3 affords complete trans selectivity and yields up to 97% of the corresponding 3‘-alkyl aziridines 4 and 5, while the cyclization of 8 affords a mixture of diasteroisomers 11, 12 in 86/14 ratio and a 95% yield. A mechanistic study has been made to rationalize the trans selectivity observed in the cyclization of 2 and 3. AM1 computations allow us to deduce that the reaction proceeds through cyclic titanium or aluminum enolate formation, and they reveal that enolates leading to tr...

Trans -Diastereoselective synthesis of 3-phthalimido β-lactams via a two step-staudinger reaction

New conditions for the Staudinger reaction provide N-unsubstituted-3-phthalimido-β-lactams in satisfactory yields with complete trans-selectivity.