| Summary: | A number of oxygenated heterocycles have been described in nature as having a myriad of biological activities. Owing to these biological activities and their complex structure, these compounds are of interest to us and the preparation of selected oxygenated heterocycles is described in this thesis. Three main sections form this thesis, with each representing a class of oxygenated heterocycle. The first part of the thesis deals with pyranonaphthoquinone analogues where a model study was performed to construct the skeleton of the isochromane kalafungin. The synthesis of isochromane 6,9-dimethoxy-3,3a,5,9b-tetrahydro-2H-furo[3,2-c]isochromen-2-one was successfully achieved from commercially available 2,5-dihydroxybenzoic acid in an overall yield of 9.5%. The key steps employed in the synthesis of the isochromane were a cross metathesis reaction between (2-allyl-3,6-dimethoxyphenyl)methanol and ethyl acrylate to afford the α,β-unsaturated ester (E)-ethyl-4-(2-(hydroxymethyl)-3,6-dimethoxyphenyl)but-2-enoate which, after several synthetic steps, was converted to the isochromane via a radical induced lactonization using a hypervalent iodine reagent. The success of this route led us to the preparation of iscochromane (3aR, 5R, 9bR)-6,9-dimethoxy-5-methyl-3,3a,5,9b-tetrahydro-2Hfuro[ 3,2-c]isochromen-2-one. Our initial aim was to enzymatically resolve intermediate racemic alcohol 1-(2-allyl-3,6-dimethoxyphenyl)ethanol, however, the use of Candida antarctica lipase B (CALB) to facilitate the kinetic resolution was not as successful as we hoped. Therefore, using racemic alcohol 1-(2-allyl-3,6-dimethoxyphenyl)ethanol and the key reaction conditions developed in the model study of 6,9-dimethoxy-3,3a,5,9b-tetrahydro-2H-furo[3,2-c]isochromen-2-one, we successfully prepared isochromane (3aR, 5R, 9bR)-6,9-dimethoxy-5-methyl-3,3a,5,9btetrahydro 2H-furo[3,2-c]isochromen-2-one in an overall yield of 0.4%, albeit racemically. The second part of this thesis involved the use of nitroalkanes as precursors to spiroketals. In this ...
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