Studies On The Efficient Syntheses Of Isoxazoles,Isoxazolines And Total Syntheses Of Dihydropyrone Natural Products

This dissertation aims at the studies on the efficient and regioselective one-pot syntheses of isoxazoles and 2-isoxazolines, and 2-isoxazolines were demonstrated as versatile synthons in organic synthesis. Meanwhile, total syntheses of (+)-Strictifolione and (6R)-6-[(4R,6R)-4,6-Dihydroxy-10-phenyldec-1-enyl]-5,6-dihydro-2H-pyran-2-one were also studied. This dissertation consists of the following four chapters:Chapter 1. Protecting-group-free synthesis and its applications in organic synthesis (review)Protecting-group-free syntheses and strategies aiming for achieving this goal were highlighted in this review. The invention of chemoselective methodologies is crucial to the execution of protecting-group-free syntheses, and recent advances in this area are also highlighted.Chapter 2. Synthetic studies toward efficient and regioselective one-pot synthesis of isoxazoles.The bioactivity, synthetic applications and synthetic methods of isoxazoles were introduced briefly.An efficient and regioselective one-pot synthesis of 3-substituted and 3,5-disubstituted isoxazoles has been developed from readily availableα,β-unsaturated aldehydes/ketones and TsNHOH. This novel strategy is associated with readily available starting materials, mild conditions, high regioselectivity and wide scope.Chapter 3. Synthetic studies toward efficient and regioselective synthesis of 2-isoxazolines and its applications in organic synthesisThe bioactivity, synthetic applications and synthetic methods of 2-isoxazolines were introduced briefly.Based on the work of synthesis of isoxazoles, an efficient approach for the highly regioselective synthesis of a diverse array of 2-isoxazolines was developed. This methodology tolerates a wide variety of functional groups. Furthermore, 2-isoxazolines were demonstrated as versatile synthons for the syntheses of isoxazoles,β-hydroxy oximes, N-aryl-β-lactams and y-amino alcohols. In addition, preparation of optically active y-amino alcohols via asymmetric reductive ring-opening reactions was also attempted.Chapter 4. Concise Total Syntheses of (+)-Strictifolione and (6R)-6-[(4R,6R)-4,6-Dihydroxy-10-phenyldec-1-enyl]-5,6-dihydro-2H-pyran-2-oneThe structural character, bioactivity and work of our group in synthesis of dihydropyrone natural products were introduced briefly.Starting from readily available 3-butenal, concise total syntheses of (+)-Strictifolione and (6R)-6-[(4R,6R)-4,6-Dihydroxy-10-phenyldec-l-enyl]-5,6-dihydro-2H-pyran-2-one have been achieved based on the strategic application of one-pot double allylboration and ring-closing metathesis reactions. The total syntheses proceeded in only 5 steps (23% overall yield) and 7 steps (21% overall yield), respectively, and represent the shortest syntheses of the two compouds reported to date.