Aluminium triflate-mediated reactions of glycals: towards chiral multicyclic products
Institution: | University of Johannesburg |
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Department: | |
Year: | 2015 |
Keywords: | Substitution reactions; Organic compounds - Synthesis; Enantioselective catalysis; Lewis acids |
Record ID: | 1466579 |
Full text PDF: | http://hdl.handle.net/10210/13698 |
The bridged chiral benzopyrans were strategically ring opened via acetolysis to yield either galactose based chromenes or chromans, depending on the reaction conditions. A proposal relating to the mechanism of this selective ring opening acetolysis is discussed. The benzopyrans (chromenes, chromans and bridged chiral benzopyrans) were de-acetylated via triethyl amine catalysed transesterification. Interestingly, the chromenes did not yield the anticipated hydrolysis product (triol) but a new class of bridged chiral benzopyrans which were a result of intramolecular oxa-Michael addition. A chromene that formed during the selective ring opening of the bridged chiral benzopyrans was employed to develop a method for the synthesis of a carbohydrate derived oxepane. The oxepane synthesis was achieved, albeit in the face of numerous challenges from side reactions. The difficulties encountered in the synthesis are discussed...