Stereoselective Synthesis of trans-4,5-Disubstituted Oxazolidin-2-ones by Intramolecular Conjugate Addition of N-p-Toluenesulfonyl Carbamates.

p-Toluenesulfonyl carbamates (2a-d) were prepared starting from allylic alcohols (3), in which the double bond is conjugated with an electron withdrawing group. In the presence of a catalytic amount of DBU, an intramolecular cyclisation occurred, leading to trans-4,5-disubstituted oxazolidin-2-ones (1a-d) with total stereoselection, which can be precursors of syn-4-hydroxy-3-amino acids.

Synthesis and reactivity of the novel hydride derivative RhHCl(TIMP3) (HTIMP3 = tris[1-(diphenylphosphino)-3-methyl-1H-indol-2-yl]methane)

The reaction of HTIMP(3) (HTIMP(3) = tris[1-(diphenylphosphino)-3-methyl-1H-indol-2-yl]methane) with [RhCl(COD)](2) and Rh(acac)(CO)(2) produces RhHCl(TIMP(3)) (1H) and Rh(TIMP(3))(CO) (2), respectively, both exhibiting tetradentate kappaC,kappa(3)P-coordination of the TIMP(3) moiety. The reaction of RhHCl(TIMP(3)) with nucleophiles (L) in the presence of AgBF(4) or AgPF(6) produces different compounds depending on the nature of L. Indeed, cationic Lewis adducts of formula [RhH(L)(TIMP(3))](+) ((2H+)-(5H+)) are obtained when L is CO, CNCH(2)Ph, pyridine or CH(2)CHCN. On the other hand, when the incoming nucleophile is CH(3)COOH the hydride-free complex [Rh(CH(3)COO)(TIMP(3))](+) ((6+)) is o…

Synthesis of unsaturated β-amino acid derivatives from carbamates of the Baylis–Hillman products

Abstract By treatment with a catalytic amount of DBU in DCM, N-p-toluenesulphonyl carbamates 6a–c , prepared starting from the corresponding Baylis–Hillman adducts, gave (E)-2-(p-toluenesulphonylaminomethyl)propenoates 3a–c , exclusively. On the contrary, changing DABCO for DBU, 2-methylene-3-p-toluenesulfonylamino esters 4a–f were obtained in good yield starting from N-p-toluenesulphonyl carbamates 6a–f . In analogy, N-acyl carbamates 9a–f were treated with DABCO in DCM to give the 2-methylene-3-acylamino esters 5a–f .

Homochiral oxazolidin-2-ones and imidazolidin-2-ones by tandem nucleophilic addition–conjugate addition

Abstract Treatment of both primary alcohols 1a , b and secondary amines 1c , d , tethered to a Michael acceptor with ( R )-phenylethyl isocyanate in the presence of DBU gave in good yield and high stereoselection diastereomeric mixtures of oxazolidin-2-ones 2a , b and 3a , b and imidazolidin-2-ones 2c , d and 3c , d , respectively. The cyclisation reaction was studied computationally by ab initio quantum mechanical methods. The observed stereoselectivity was explained on the basis of the different stability of both anions and transition states leading to 2a and 3a , respectively. The usefulness of the method was proven by conversion of 2a into the enantiomerically pure bioactive amino acid …

ChemInform Abstract: Synthesis of Unsaturated β-Amino Acid Derivatives from Carbamates of the Baylis-Hillman Products.

Abstract By treatment with a catalytic amount of DBU in DCM, N-p-toluenesulphonyl carbamates 6a–c , prepared starting from the corresponding Baylis–Hillman adducts, gave (E)-2-(p-toluenesulphonylaminomethyl)propenoates 3a–c , exclusively. On the contrary, changing DABCO for DBU, 2-methylene-3-p-toluenesulfonylamino esters 4a–f were obtained in good yield starting from N-p-toluenesulphonyl carbamates 6a–f . In analogy, N-acyl carbamates 9a–f were treated with DABCO in DCM to give the 2-methylene-3-acylamino esters 5a–f .

Oxidation of aminodiols mediated by homogeneous and heterogeneous TEMPO

The conversion of amino diols to aminohy- droxy acids by oxidation of the primary hydroxy group mediated by homogeneous and heterogeneous TEMPO (2,2,6,6-tetramethylpiperidine 1-oxyl radi- cal) is reported. The synthesis uses NaOCl as primary oxidant and TEMPO, either dissolved in the homoge- neous phase or entrapped in a sol-gel matrix, as cata- lytic mediator. Homogeneous TEMPO is suitable for the oxidation of aliphatic methylamino diols, while the hybrid organic-inorganic silica sol-gel catalysts are more selective mediators for the oxidation of ben- zylic amino diols like the potent antibiotic chloram- phenicol which, under homogeneous conditions, are unselectively oxidized to benzoic ac…

AC3-Symmetric Palladium Catalyst with a Phosphorus-Based Tripodal Ligand

An Unprecedented Iridium(III) Catalyst for Stereoselective Dimerisation of Terminal Alkynes

A novel iridium(III) hydride complex, IrHCl(TIMP 3 ) {HTIMP 3 = tris[1-(diphenylphosphino)-3-methyl-lH-indol-2-yl]methane) was prepared and fully characterized in both the solid state and in solution. Chloride abstraction by silver cations provides a more reactive compound, [IrH-(TIMP 3 )][BF 4 ], which can react with pyridine (py) and phenylacetylene to yield the complexes [IrH-(TIMP 3 )(py)][BF 4 ] and [Ir(PhCH=C-CH=CHPh)-(TIMP 3 )][BF 4 ], respectively. Interestingly, IrH-(TIMP 3 )(py)][BF 4 ] efficiently catalyses the stereoselective dimerisation of model terminal alkynes to the 1,4-disubstituted (E)-but-1-en-3-yne only.