0000000000132965
AUTHOR
Mario Orena
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 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 .
Synthesis of chiral oxazolidin-2-ones from N-alkoxycarbonyl amino epoxides: a computational studyElectronic supplementary information (ESI) available: structures of localized transition states. See http://www.rsc.org/suppdata/p1/b2/b203702e/
threo-N-Alkoxycarbonylamino epoxides 5a–d, containing the oxazolidine moiety, were converted into trans-4,5-disubstituted-2-oxazolidin-2-ones 2 with total regio- and stereoselection by means of nucleophilic intramolecular attack of the carbamate moiety to the protonated oxirane ring. Theoretical calculations confirmed both the regioselection and the preference of the cyclocarbamation reaction vs. the intermolecular attack by the solvent, arising from different behaviour in comparison with the analogous iodonium ions.
1,3-Oxazin-2-ones vs tetrahydrofurans by iodocyclisation of 2-alkoxycarbonylamino-3-alken-1-ols
Abstract Iodocyclisation of primary homoallylic alcohols 2a – d , containing either a 2- t -butoxy- or a benzyloxycarbonylamino group, was studied, in order to establish the nucleophilic group involved in cyclofunctionalisation. In fact, the N - t -Boc derivative 2a gave the oxazinone 3 , exclusively, whereas starting from the N -Cbz derivative 2b a diastereomeric mixture of substituted tetrahydrofurans 4 and 5 resulted in ratios depending upon the reaction conditions. These results were rationalised by means of computational methods. On the contrary, migration of both the t -butyl or benzyl group to the hydroxy group was observed when both 2c and 2d underwent cyclisation to give the corres…
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 .
Novel enantiomerically pure 2-amino-1,4-diols from chiral 4-hydroxymethyl-5-iodo-1,3-oxazin-2-ones
Abstract Reduction of (4 S ,5 S ,6 S )-4-hydroxymethyl-5-iodo-6-methyl-1,3-oxazin-2-one 2a and (4 S ,5 S ,6 R )-4-hydroxymethyl-5-iodo-6-phenyl-1,3-oxazin-2-one 2b with tributyltin hydride in ethanol afforded 1,3-oxazin-2-one 3a and 1,3-oxazolidin-2-one 4b , respectively. Hydrolysis of 3a and 4b under basic conditions led to enantiomerically pure aminodiols 1a and 1b . Reduction of 2b in refluxing toluene led to the unexpected bicyclic tetrahydrofuro[3 a , d ]-1,3-oxazolidin-2-one 5 as the sole product.
Highly regio- and stereoselective iodocyclization of chiral 3-alkoxycarbonyl-4-propenyl-2,2-dimethyl-1,3-oxazolidines: a computational investigation
The iodocyclization of allylic carbamates 3a and 3b proceeded with high regio- and stereoselection to give 2-oxobicyclo[4.3.0]nonane 5a as the major product. Both the regio- and diastereoselection of the reaction were investigated with the help of molecular mechanics and quantomechanical calculations. The energetic difference between the competing transition states TS-5a and TS-5b is in good agreement with the experimental results and from the calculated transition structures it appears that steric factors direct the discrimination.