(1R)-Camphor based tridentate Schiff Bases of 3-exo-Aminoisoborneol [SBAIB] and (1R)-α-Pinene based tetradentate Bipyridyldiol: Versatile chiral catalysts in Asymmetric synthesis

• Main Author: Ramalingam Boobalan
• Other Authors: Chinpiao Chen
• Format: Others
• Language: en_US
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/k63wz4

博士 === 國立東華大學 === 化學系 === 102 === This thesis describes mainly the study of synthesis of conformationally rigid camphor derived Schiff bases of 3-exo-aminoisoborneol [SBAIB] and their catalytic efficiency towards various asymmetric reactions. This study developed the high yielding condensation protocol for synthesis of Schiff bases from 3-exo-aminoisoborneol [AIB] and 2-hydroxy-aromatic aldehydes. X-ray crystal structures of SBAIB-a L1 and SBAIB-b L2 were confirmed the general structural skeleton of all of the synthesized nine Schiff bases (L1 - L8 and (−)-L1). The transition metal complexes of SBAIB have tested for various asymmetric transformations. They were found to be versatile and exhibit excellent level of chiral induction in many stereoselective reactions. In situ generated Zinc-SBAIB complexes were effectively catalysize enantioselective phenylacetylene addition reaction towards various aldehydes. Under the optimal conditions, L1, (+)-SBAIB-a, was found to be an excellent catalyst for this enantioselective transformation without utilizing either achiral additives or Ti(OiPr)4. This approach yields (R)-propargylic alcohols in extremely high yield (up to 99%) and excellent ee (up to 92%). The corresponding (S)-propargylic alcohols were synthesized in good to high enantioselectivities (up to 91%) and excellent yields (up to 99%) using opposite enantiomer (−)-SBAIB-a, (−)-L1. The stable and non-moisture sensitive bifunctional copper complex of aminoisoborneol Schiff bases [CuSBAIB]2 were synthesized and among them, [Cu(SBAIB-d)]2 was detected as the highly efficient catalyst for asymmetric direact Henry reaction of numerous aldehydes. The 1 mol% of this catalyst produces expected Henry products in high yields (up to 99%) with excellent enantioselectivities (up to 98% ee). The utility of [Cu(SBAIB-d)]2 catalyst was also extended to the Henry reaction with nitroethane and 1-nitropropane that furnished corresponding products in moderate to high yields (up to 99%) with moderate to high enantioselectivities of syn (up to 98% ee) and anti (up to 98% ee) diastereomers. Iron(III)-SBAIB complexes were synthesized and its catalytic nature tested for enantioselective hydrophosphonylation of various aldehydes. In an optimized reaction condition, 5 mol% of [FeCl(SBAIB-d)]2 produces α-hydroxy phosphonates in excellent enantioselectivitity (up to 99%). This was the first Fe-catalyst that exhibits highest enantioselectivity for hydrophosphonylation reaction of aldehydes. This mild Fe-SBAIB catalytic system has advantages of giving higher chiral induction as compare to metal complexes of 1,2-aminoalcohols that are synthesized from aminoacids. The last part of the thesis descirbes the development of an efficient and concise synthetic route for the versatile O,N,N,O-tetradentate bipyridyldiol ligand starting from naturally available and cheap α-pinene. The design of earlier nucleophilic addition of half molecule of bipyridine followed by homocoupling made shorten the synthetic route over the sequential double Kröhnke annulation procedure for the synthesis of same ligand. The remarkable key step in this synthesis was a seal tube reaction of conversion of pinene-pyridone into pinene-chloropyridine by phosphorous oxychloride.