Mercedes Crego

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.

A receptor for aromatic acids and amides

A dinitrotoluic residue has been introduced onto an hydrogen bonding aromatic acid receptor to achieve stacking and charge-transfer interactions. This new receptor shows large differences in association constants with aromatic guests in CDCl3 ranging from 1.6 × 103 with isophthalic acid methyl ester to 1.5 × 106 with p-dimethylamino benzoic acid.

Three complexing agents for ureas and formamides

Abstract Three cleft type hydrogen bonding receptors were prepared, with slightly different geometries due to the presence of either methylene, oxygen, or sulfur. All three are able to complex urea, one with the methylene group being the best suited. Benzyl formamide, probably due to its smaller cleft, is better associated to the oxygen compound.

Improved receptors for dibutylmalonic acid

Abstract New molecular receptors with a dibenz[c,h]acridine skeleton bearing functional groups complementary to dibutylmalonic acid have been developed.

Lactone receptors with catalytic activity

Abstract Three cleft-type receptors have been prepared that associate 2(5H)-furanone in benzene. These complexes show greater reactivity toward pyrrolidine nucleophilic addition than the furanone itself, probably due to stronger hydrogen bonds in going to the transition state.

Chromenone derivatives as receptors for N-benzoylamino acids

The chromenone derivative 5, easy to synthesize from 2-hydroxyacetophenone 1, has been used to prepare the hosts 7–10 and 12. These combine three hydrogen bonds, π-stacking and chargetransfer interactions for the complexation of N-benzoylamino acids in CDCl3.

Dibutylmalonic acid receptors with decarboxylative activity

Abstract Dibutylmalonic acid receptors have been designed to optimize their catalytic decarboxylative activity in the pressence of isoquinoline. A phosphonamide

Chiral receptor for N-benzyloxycarbonyl aminoacid derivatives

Abstract Chiral cleft-type receptors for N-benzyloxycarbonyl aminoacid derivatives have been prepared. Discrimination between aminoacids with non-polar side chains is modest. Better chiral recognition is obtained with serine. A receptor with an aminopyridine unit allows a high association constant with aspartic acid.

Cleft type receptors with catalytic activity in amide deuteration

Abstract Cleft type receptors have been prepared with a significant activity in amide deuteration. Charge-transfer and hydrogen bonds seems to be responsible for the catalytic activity.