Browsing by Author "Ho, Tse-Lok"

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A new glycosylation method based on 8-quinolyl glycosides
(2006-12-01)
Chang, Chih-Wei
;
Ho, Tse-Lok
;
應用化學系
;
Department of Applied Chemistry
A synthesis of two 8-quinolyl glycosides (1 a, 2a) and demonstration of their service as glycosyl donors are described. These stable compounds react with various alcohols in the presence of metal salts at 60 degrees C for 16-48 h to furnish the coupling products in excellent yields (88-96%).
Concise Synthesis of Yashabushidiol A and (+/-)-Diospongin A
(2012-03-01)
Ho, Tse-Lok
;
Tang, Bin
;
Ma, Guohua
;
Xu, Pengfei
;
應用化學系
Synthesis of (+/-)-diospongin A has been achieved from the (2SR,4RS)-pentane-1,2,4,5-tetraol in six steps. An intermediate has also been converted into yashabushidiol A. This work features a desymmetric cyclization and reduction of a meso-1,7-diarylheptanoid precursor to furnish the desired cis-2,6-disubstituted tetrahydropyran.
Deformative Transition of the Menschutkin Reaction and Helical Atropisomers in a Congested Polyheterocyclic System
(2014-11-07)
Chang, Yung-Yu
;
Ho, Tse-Lok
;
Chung, Wen-Sheng
;
應用化學系
;
Department of Applied Chemistry
A 4,7-phenanthroline polycyclic 1A designed for probing the limits of the Menschutkin reaction was synthesized in a six-step sequence. The rotational barrier of the phenyl ring nearby the N-methyl group in rac-2A was estimated to be >= 18.1 kcal/mol from VT-NMR experiments, making them a new type of helical atropisomer. The methylation rate constants of 9 and 1A with MeI was found to be 2.22 x 10 (4) and 9.62 x 10 (6) s(1) mol(1) L, respectively; thus, the formation rate of (P/M)-2A is one of the slowest rates ever reported for a Menschutkin reaction. The N-methyl protons in (P/M)-2A exhibit a significant upfield shift (Delta delta 1.0 ppm) in its H-1 NMR, compared to those without a nearby phenyl, indicating a strong CH-pi interaction is involved. Conformational flexibility in dipyridylethene 9 is clearly shown by its complexation with BH3 to form helical atropisomers (P,P/M,M)-10. The pKa values of the conjugate acids of 1A and 9 in acetonitrile were determined to be 4.65 and 5.07, respectively, which are much smaller compared to that of pyridine 14a (pK(a) = 12.33), implying that the basicity, nucleophilicity, and amine alkylation rates of 1A and 9 are markedly decreased by the severe steric hindrance of the flanking phenyl rings in the polyheterocycles.
Fiesers' reagents for organic synthesis.
(Wiley, 2007)
Ho, Tse-Lok
Fiesers' reagents for organic synthesis.
(Wiley, 2004)
Ho, Tse-Lok
Fiesers' reagents for organic synthesis.
(Wiley, 1999)
Ho, Tse-Lok
Fiesers' reagents for organic synthesis.
(Wiley, 2003)
Ho, Tse-Lok
Fiesers' reagents for organic synthesis.
(Wiley, 2000)
Ho, Tse-Lok
Fiesers' reagents for organic synthesis.
(Wiley, 1999)
Ho, Tse-Lok
The Synthesis of Rigid Polycyclic Structures for the Study of Diatropic or Steric Effects of a Phenyl Ring on CF Bond
(2013-12-20)
Chang, Yung-Yu
;
Ho, I-Ting
;
Ho, Tse-Lok
;
Chung, Wen-Sheng
;
應用化學系
Polycyclic compounds 1a-c were synthesized to study the diatropic effects of a flanking phenyl ring on nearby CH and CF bonds. F-19 NMR spectra of 1b and 1c were strongly deshielded compared with those of the ring-opened compounds 3b, 7b, and 7c. DMol3 calculations on 1a-c provided quantitative bond lengths and torsional angles to support the conclusion that the downfield shifts in the F-19 NMR spectra are mainly due to steric interactions between the CF bonds and the pi clouds of the phenyl ring(s).
Total Synthesis of Quebrachamine through Macrolactamization
(2014-05-01)
Hsu, Shih-Wen
;
Cheng, Hsiu-Yi
;
Huang, An-Chi
;
Ho, Tse-Lok
;
Hou, Duen-Ren
The total synthesis of quebrachamine was achieved through the macrolactamization of cis-2-alkenylated indole 17, which was prepared by a Sonogashira reaction between indole 5b and piperidine 11 followed by cis-hydrogenation. We found that stoichiometric copper(I) iodide limited the undesired Glaser-type homocoupling of alkyne 11 that would otherwise take place during the Sonogashira coupling. This direct approach allowed the total synthesis in ten linear steps starting from commercially available chemicals. Conditions for the reduction of lactam 19 by lithium aluminiumhydride were adjustable, so that either (+/-)-quebrachamine or the analogue (+/-)-kopsiyunnanine D was prepared.