Joaquín R. Morán

A macrocyclic receptor for the chiral recognition of hydroxycarboxylates

Good chiral recognition of hydroxycarboxylates such as lactic or mandelic acids has been achieved with a macrocyclic receptor, readily available from a known bis-chromenylurea and a spirobifluorene linker. Resolution of the receptor racemic mixture was carried out taking advantage of its complexing properties with (R)-mandelic acid tetramethylammonium salt on a TLC plate.

A CYCLOHEXANE SPACER FOR PHOSPHATE RECEPTORS

Abstract A cyclohexane tricarboxylic acid is shown to be a good spacer for phosphate guests. The combination of 8-aminochromenone-2-carboxamide groups with the cyclohexane spacer leads to a versatile receptor which sets six hydrogen bonds with either phosphonic acids or phosphates. Large association constants are obtained for this receptor in DMSO and methanol when tetraalkylammonium phosphates are used as guests.

Guanidinium catalyzed conjugate addition of pyrrolidine to unsaturated lactones

Abstract More than a 8-fold reduction in half-life can be observed for conjugate additions of pyrrolidine to α,β-unsaturated lactones in the presence of catalytic amounts (0.1 equiv.) of bicyclic chiral guanidinium salts 1 , presumably by selective hydrogen-bond stabilization of the transition state.

Imidazolidinone intermediates in prolinamide-catalyzed aldol reactions

The reaction between acetone and 4-nitrobenzaldehyde catalyzed by aniline prolinamide 1 was studied in depth. Working in different solvents with equimolar amounts of reagents and monitoring the reaction by 1H NMR, we detected and identified several imidazolidinones, such as those of the acetone 4, the aldol products 5a and 5b, and aldehydes 10a and 10b. According to our results, these compounds could influence the reaction rate and diminish product enantioselectivity. Furthermore, acetone imidazolidinone 4 was seen to react with 4-nitrobenzaldehyde to furnish the aldol product 3. This reaction can be catalyzed by different nucleophiles and acids. In fact, strong acids such as camphorsulfonic or trifluoroacetic acid, convert imidazolidinones into iminium salts and afford more enantioselective aldol reactions when different aromatic prolinamides are used. Enantiomeric excesses of ca. 82% are reached.

Helmanticine, a phenylpropanoid from Thapsia villosa

Abstract Helmanticine, a new phenylpropanoid esterified by angelic and 2,3-dihydroxy-2-methylbutyric acids, was isolated from Thapsia villosa and its full structure established by spectroscopic methods and chemical transformations. Hydrocarbons, 12-nonacosanone, sitosterol and latifolone were also isolated.

Synthesis of Monoacylated Derivatives of 1,2- Cyclohexanediamine. Evaluation of their Catalytic Activity in the Preparation of Wieland−Miescher Ketone†

Ureas, carbamoyl derivatives, amides, and sulfonamides can be easily prepared from the strained (R,R)-cylohexanediamine urea (1) in high yield, leaving a free amino group that shows good catalytic activity in intramolecular aldol condensations. The preparation of Wieland-Miescher ketone has been studied with these catalysts.

CHIRAL RECOGNITION OF TARTARIC ACID DERIVATIVES WITH CHROMENONE-BENZOXAZOLE RECEPTORS AND A SPIROBIFLUORENE SPACER

Abstract The combination of a spirobifluorene spacer with two chromenone-amino-benzoxazole binding arms affords a chiral cleft type receptor. Due to the strong chiral recognition, resolution of the receptor racemic mixture can be achieved by means of a silica gel TLC plate impregnated with optically pure dibenzoyl tartaric acid. Slow complex formation on the 1 H-NMR scale with this host at −10°C allows observation of different signals for free and complex guests in 1 H-NMR.

Readily available chromenone receptors for carboxylates

Abstract Several carboxylate group receptors able to bind syn and anti electron lone pairs have been prepared making use of an aminochromenone fragment. Symmetric ureas and sulfuryl amides permit the establishment of four linear hydrogen bonds with the carboxylate. The flat geometry of the sulfuryl amides complexes and the higher acidity of their hydrogens yield the best association constants.

Thiobenzophenone and tetracyanoethylene

Abstract The title reaction furnished the yellow 3,4-dicyano-2,5-bis(diphenylmethyleneamino)-thiophene and a red precursor which contains one more sulfur atom; structures and mechanism are discussed.

Tovarol and other germacrane derivatives from Thapsia villosa

Abstract Four tovarol, two epoxytovarol (= shiromodiol) and one diepoxytovarol esters were the new germacrane esters isolated from the roots of Thapsia villosa var. minor . The structures of these substances were assigned on the basis of spectral data and chemical correlations with shiromodiol. The acid catalysed rearrangement of tavarol yielded 1(10),4-bulgaradiene-8-ol.