The use of biomasa in asymmeric synthesis

VALERIA CORNE; MARÍA M. ZANARDI; DAVID F. LLOMPART; MARÍA C. BOTTA; ROLANDO A. SPANEVELLO; ALEJANDRA G. SUÁREZ

Golden

Otro; American Chemical Society Summer School on Green Chemistry and Sustainable Energy.; 2010

American Chemical Society

  Biomass is a widely available raw material which has been recognized as an important source of fuels and chemical products. By far, carbohydrates are the major annually renewable biofeedstocks from which to develop viable organic chemicals that are to replace those derived from fossil sources.Carbohydrates probably play an unsurpassed role as chiral auxiliaries in asymmetric synthesis regarding optical purity, number of stereogenic centers, availability and economics. Levoglucosenone  is a versatile and readily available member of the carbohydrate derived chiral pool, which has been used as chiral synthon in the synthesis of a wide variety of compounds.Asymmetric epoxidation of olefins represents a powerful strategy for the synthesis of enantiomerically enriched epoxides. Among the different epoxidation strategies, chiral dioxiranes generated in situ from potassium peroxomonosulfate (Oxone) and chiral ketones have appeared to be promising reagents for organocatalytic asymmetric epoxidations, particularly for trans-olefins bearing no allylic alcohol groups.The catalyst 4 was obtained by cis- dihidroxilation of 1 followed by introduction of the ketal protection group. The epoxide 5 was prepared by reaction of 1 with sodium hipoclorite. The chiral ketone 6 was obtained by reduction of levoglucosenone followed by bromination reaction. The catalyst 7 was prepared by two-step bromination of 1, followed by a Diels-Alder reaction with anthracene. These ketones are being tested in the asymmetric epoxidation reaction of trans-stilbene.