HIGHLY EFFICIENT CHIRAL INDUCTORS DERIVED FROM BIOMASS

ZANARDI, M. M; SAROTTI, A. M.; SUÁREZ, A. G.; SPANEVELLO, R. A.

Montevideo, Uruguay

Workshop; IFS/OPCW Workshop Chemistry in Nature - Natural Resources: Chemical, Biological and Enviromental Aspects; 2008

International Foundation for Science and Organization for the Prohibition of Chemical Weapons

The generation of useful chemicals from cellulosic materials have been investigated through the pyrolysis of acid-pretreated waste paper. Levoglucosenone (1), a bicyclic enone, is the major product obtained from the pyrolysis of cellulose-containing materials. During the last decade this versatile and readily available member of the carbohydrate derived chiral pool, has been used as chiral synthon in the synthesis of a wide variety of natural and unnatural products, some of them showing interesting biological activities [1]. Our interest in this field is focused on the potential use of this chiral building block in the synthesis of asymmetric inductors and the study of their applications in asymmetric organic transformations Starting from 1 as chiral starting material we synthesized different alcohols and 1,2-amino alcohols in a straightforward and efficient manner. In general, the inductors where prepared by a cycloaddition reaction of levoglucosenone with different substituted anthracene derivatives. The chiral alcohols 2-5 were obtained by reduction of the ketone functionality and the inductive capacity were tested as chiral auxiliaries in Diels-Alder reactions. For this reason we examined the use of the corresponding acrylic ester derivatives as dienophiles and different cyclic and acyclic dienes. The products were obtained with excellent yields and selectivity with diastereomeric excess up to 98% [2]. The chiral amino alcohols 6 were obtained from the corresponding ketone precursor by a Corey-Chaykovsky reaction followed by a ring opening of the epoxide with piperidine. The catalysts 7 and 8 were prepared by a cycloaddition reaction of 1 with 9-aminoanthracene and subsequent reduction of the ketone. The chiral ligands were tested in the asymmetric alkylation reaction of benzaldehyde with diethylzinc with good enantioselectivities. These derivatives are the first examples of the use of levoglucosenone in the preparation of chiral inductors. The level of induction obtained, in addition to the fact that the starting material is inexpensive, makes this system an excellent model to be further exploited in other asymmetric reactions and a starting point for new chiral templates.