Synthesis of oxa- and aza-cycles is a topic of contemporary interest owing to the presence of these moieties in structurally challenging and biologically important natural products. Our group is involved in developing strategies for their synthesis using vinylogous carbonates and carbamates under radical as well as non-radical conditions. In this regard, we have developed a highly stereoselective synthesis of new oxa-cages and angular oxa-triquinanesvia alkyl radical cyclisation to vinylogous carbonates. To expand the scope of vinylogous carbonates and carbamates in non-radical pathways, a highly diastereoselective method for the synthesis of cyclopropafuranones and cyclopropapyrrolidinones from vinylogous carbonates and carbamates, respectively, has been established. These donor-acceptor substituted cyclopropanes (DACs) have been converted into diversely functionalized THFs, THPs, lactones, pyrrolidine, piperidine and lactam derivatives by regioselective ring opening of the cyclopropane ring. An efficient strategy for the synthesis of THF, THP and oxepane derivatives has been developed employing a tandem SN2-Michael addition to vinylogous carbonates. Further, we have shown that the intramolecular Pictet-Spengler type cyclization of the indole moiety to the vinylogous carbonates under Lewis acidic conditions can be effected leading to N-fused oxazino indoles. We have demonstrated that Lewis acid mediated reductive etherification can be used for gaining stereoselective access to diverse array of 1,4-heterocycles like morpholines, which are important pharmacophores. Very recently, we have developed divergent synthesis of N-fused indolylidine, indole, and indoline derivatives using alkyne iminium ion cyclization. The talk will highlight some of thesestudies for the stereoselective construction of bioactive oxa- and aza-cycles.
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