Executive Summary : | The study proposes an enantioselective synthesis of α-quaternary stereocenter containing oxa-cycles via an intramolecular oxa-Michael addition of substrates with a β-substituted α,β-unsaturated carbonyl moiety. This method aims to provide a versatile method for obtaining various oxa-cycles, such as tetrahydrofurans (THFs), tetrahydropyrans (THPs), isobenzofurans, and isochromans with α-tetrasubstituted stereocenters. The use of bisnucleophiles with multiple nucleophilic centers, such as N-protected hydroxylamine, is also proposed. The enantio- and diastereoselective synthesis of chiral 1,2-oxazines will be achieved using ortho-formyl chalcone as a potential substrate. Additionally, 1,4-bis-enones will be used as substrates for enantio- and diastereoselective oxa- and aza-Michael reactions to provide chiral 1,2-oxazines with two chiral centers. The study also proposes a strategy for the synthesis of chiral benzo[1,3]thiazine analogues using amino-thiourea/squaramide organcatalysts. The hypothesis is that isothiocyanato containing enone will follow a nucleophilic addition to isothiocyanato moiety followed by asymmetric intramolecular sulfa-Michael addition, providing an elegant method for the synthesis of chiral benzo[1,3]thiazine. The reaction of unsymmetrical active methylene units to isothiocyanato containing enone will be executed for an asymmetric Michael addition followed by diastereoselective 1,2-addition to isothiocyanate moiety, providing an excellent method for the enantioselective synthesis of 2-thioquinolones with an all carbon quaternary stereocenter. |