José Sepúlveda-Arques

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 .

Theoretical Study of the Reaction of Dimethyl Acetylenedicarboxylate with 1-Methyl-2-(1-substituted vinyl)pyrroles

Abstract A theoretical study of the transition structure for the electrophilic attack step of the 1-methyl-2-vinylpyrrole to dimethyl acetylenedicarboxylate is reported with analytical gradients at AM1 and PM3 semi-empirical levels and ab initio at 3-21G level. The geometry, electronic structure, and vector components are qualitatively computer level and model independent The competition of the Michael addition reactions and Diels-Alder reactions of 1-methyl-2-(1-substituted vinyl)pyrroles with dimethyl acetylenedicarboxylate has been studied at the PM3 semi-empirical level.

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.

Experimental and theoretical investigations for the regio and stereoselective transformation of trans 1,2,3-trisubstituted aziridines into trans oxazolidin-2-ones

The regio and stereoselective transformation of trans 1,2,3-trisubstituted aziridines into trans oxazolidin-2-ones takes place in good yield. However, the cis configuration at C2 and C3 in monocyclic aziridines is a limiting factor for this transformation. Ab initio calculations show that while the ring-opening process assisted by iodide is regioselective, the subsequent ring-closure is responsible for the retention of the configuration at the trans oxazolidin-2-one. The larger energy found for the ring-closure process for the cis aziridines accounts for the non-formation of the cis oxazolidin-2-ones.

STEREOSELECTIVE RING TRANSFORMATION OF N-ALKYL AZIRIDINES INTO OXAZOLIDIN-2-ONES

N-Alkyl aziridines react stereoselectively with di-tert-butyl diearbonate and sodium iodide in acetone to give oxazolidin-2-ones in excellent yields.

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 corresponding 5-alkoxymethyl oxazolidin-2-ones 7a , b in low yield, but with high regio- and stereocontrol.

Reaction of 3-Methylamino-1,2-diols with Dihalomethanes. Synthesis of Chiral 4-Substituted 3-Methyltetrahydro-1,3-oxazin-5-ols

Abstract Enantiomerically pure 4,5-disubstituted 3-methyltetrahydro-1,3-oxazines have been obtained by reaction of 3-methylamino-1,2-diols with dichloromethane by regioselective differentiation of hydroxyl groups.

Ring transformation of furfural into an unusual bicyclic system: Characterisation and dynamic stereochemistry of 6,7-diethoxycarbonyl-6,7-diaza-8-oxabicyclo[3,2,1]oct-3-en-2-one

Abstract 2-Formylthiophene and 3-formylindole react with diethyl azodicarboxylate to give simple products derived from reactions on the formyl group whereas 2-formylfuran reacts to give the unexpected bicyclic title compound. 1 H and 13 C NMR studies indicate that this compound undergoes a series of three dynamic conformational changes over the temperature range 50 to −90°C which are ascribed to slow rotation about the exocyclic carbamate bonds and hindered bridge inversion.

Evidence of a 1,4-dipole intermediate in the reaction of 1-phenyl-4-vinylpyrazole with PTAD

Abstract 1-Phenyl-4-vinylpyrazole reacts with 1-phenyl-1,2,4-triazoline-3,5-dione in methylene chloride to form an unstable azetidine (4). An intermediate 1,4-dipole is probably involved since, when the reaction is conducted in acetone, a 1:1:1 adduct (3) is isolated.

Synthesis of 1,3-oxazolidines and 1,3-dioxolanes by reaction of (2R, 3R)-3-methylamino-3-phenyl-1,2-propanediol with electrophiles

Abstract The chemoselective reaction of (2R, 3R)-3-methylamino-3-phenyl-1,2-propanediol 1 with dimethoxypropane and dichloromethane under different conditions are reported as useful preparative procedures, for the synthesis 1,3-oxazolidines and 1,3-dioxolanes.