Browsing by Author "CHUNG, WS"

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CONTROL OF REGIOSELECTIVITY IN THE DIELS-ALDER REACTIONS OF ALKYL-SUBSTITUTED 1,4-BENZOQUINONES BY BETA-CYCLODEXTRIN AND ITS DERIVATIVES
(1995-05-07)
CHUNG, WS
;
WANG, JY
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
The Diets-Alder reactions of benzoquinones 1-3 with penta-1,3-diene 4 and isoprene 5 are studied in aqueous cyclodextrin solutions, where highly enhanced ortho (6, 8 and 10) and meta (13, 15) regioselectivities are achieved.
FACE SELECTIVITY IN THE PATERNO-BUCHI REACTIONS OF METHACRYLONITRILE TO 5-SUBSTITUTED ADAMANTAN-2-ONES
(1995-03-01)
CHUNG, WS
;
LIU, YD
;
WANG, NJ
;
交大名義發表
;
應用化學系
The photocycloaddition of methacrylonitrile to 5-substituted adamantan-2-ones (1-X) produces two geometrically isomeric oxetanes in which the oxygen atom and the 5-substituent are in anti or syn positions. The substituent was varied from fluoro, chloro, bromo, phenyl to SiMe(3) and the product ratios, except for SiMe(3), were similar (ca. 56:44) in all instances. Structure determination of the anti and syn oxetanes were carried out by H-1 and C-13 NMR and mass spectroscopy. The structure of syn-5-bromospiro[adamantane-2,2'-oxetane] (syn-5-Br) was further supported by single-crystal X-ray crystallography. The product formation bias resulting from the attack on the zu-face is discussed in terms of transition-state hyperconjugation, but new results for photocycloaddition reactions of 5-trimethylsilyl-substituted adamantan-2-one (1-SiMe(3)), with both fumaronitrile and methacrylonitrile, show an unprecedented sigma-electron-withdrawing characteristic with this substituent.
PHOTOCYCLOADDITION OF FUMARONITRILE TO ADAMANTAN-2-ONES AND MODIFICATION OF FACE SELECTIVITY BY INCLUSION IN BETA-CYCLODEXTRIN AND ITS DERIVATIVES
(1995-02-01)
CHUNG, WS
;
WANG, NJ
;
LIU, YD
;
LEU, YJ
;
CHIANG, MY
The face selectivity in 5-substituted-adamantan-2-ones (1-Xs) can be dramatically reversed by means of inclusion into beta-cyclodextrin (beta-CD) and its heptakis(6-O-hydroxypropyl), heptakis(6-O-acetyl), heptakis(2,3,6-tri-O-methyl) and heptakis(2,3,6-tri-O-acetyl) derivatives. The 5-substituents varied from fluoro, chloro, bromo, phenyl to trimethylsilyl, and face selectivities of the oxetane formation have been found to vary with the sizes of 5-substituents and cavities of beta-CDs. A 98:2 face selectivity was achieved when 1-SiMe(3) was used as a probe. The effect observed is interpreted by assuming that the carbonyl pi-face syn to the bulky 5-substituent is partially locked by the torus of the host due to complexation of 1-X and CD. Information obtained from H-1 NMR titration and X-ray powder diffraction study on the inclusion complex is consistent with the above explanation. X-ray single-crystal structure was used to determine the oxetane structure of anti-2-SiMe(3).