Browsing by Author "Wu, AT"

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Synthesis of 2,5-disubstituted thienosultines and their thermal reactions with dienophiles and nucleophiles
(2002-12-27)
Liu, WD
;
Chi, CC
;
Pai, IF
;
Wu, AT
;
Chung, WS
The 2,5-disubstituted thienosultines (5,7-disubstituted 1,4-dihydro-1H-3lambda(4)-thieno[3,4-d][2,3]oxathiin-3-oxides) 5a-d were prepared from the corresponding dichlorides 4a-d with the commercially available Rongalite (sodium formaldehyde sulfoxylate) in 17-60% yields. When heated in the presence of electron-poor dienophiles, sultines 5a-d underwent elimination of SO2, and the resulting non-Kekule biradicals 7a-d were intercepted as the 1:1 adducts 8-12 in good to excellent yields. The pyrolysis of sultines and sulfolenes with different concentrations of dienophiles revealed that either a preequilibrium between starting reagents and biradical species or Diels-Alder and retroDiels-Alder reaction mechanisms may be involved; however, more work is necessary to establish the proposed mechanisms. Reaction of sultine 5b with nBuLi was found to undergo a nucleophilic ring-opening reaction to give sulfinyl alcohol 17 after H2O workup. When sultine 5a was heated in benzene in a sealed tube in the presence of methanol, methanol-d4, or 2-mercaptoethanol, the respective 1:1 trapping adducts 19-21 as well as the rearranged sulfolene 6a were isolated in similar amounts. The isolation of adducts 19-21 may be explained by the involvement of either biradical or ionic intermediates during the pyrolysis.
The syntheses of pyrazino-containing sultines and their application in Diels-Alder reactions with electron-poor olefins and [60]fullerene
(2000-06-02)
Liu, JH
;
Wu, AT
;
Huang, MH
;
Wu, CW
;
Chung, WS
The Diels-Alder reactions of heterocyclic o-quinodimethanes, generated in situ from 6,7-disubstituted quinoxalino[2,3-d]-[1,2 lambda(4)]oxathiine 2-oxides (6a-c), 2,3-disubstituted-8,9-dihydro-6H-8 lambda(4)-[1,2]oxathiino[4,5-g]quinoxalin-8-one (7a-c) (sultines), and pyrazinosultine (22), with electron-poor olefins and [60]fullerene are described. The heterocyclic-fused sultines 7a-c and 22 are readily prepared from the corresponding dibromides 9a-c and 24 with the commercially available Rongalite (sodium formaldehyde sulfoxylate). When heated in the presence of electron-poor dienophiles and [60]fullerene, all of the sultines underwent extrusion of SO2, and the resulting heterocyclic o-quinodimethanes (3a-d, 4a-c, and 25) were intercepted as the 1:1 adducts in good to excellent yields. The temperature-dependent H-1 NMR spectra of fullerene derivatives 31-38 show a dynamic process for the methylene protons. The activation free energies (Delta G(e)double dagger) determined for the boat-to-boat inversion of these pyrazino-containing C-60 compounds (31-34 and 38) are found to be in the range of 14.1-14.8 kcal/mol, but they are in the range of 15.2 to >17.1 kcal/mol for adducts 35-87. The activation free energies (Delta G(c)double dagger) are significantly affected by (1) the orientations and (2) the substituents of the quinoxaline rings and (3) the extended benzannulation in the arenes of C-60 adducts (see Table 2), which implies that both electronic interactions and steric effects between the aromatic addends and C-60 are important. Tautomerization of methylquinoxaline to its enamine is invoked as a rationalization for the lowering of Delta G(c)double dagger in some of the fulleroadducts.
The synthesis of naphthosultine and benzodisultines and their pyrolysis with dienophiles: Studies on o-naphthoquinodimethane and bis-o-quinodimethane
(2002-02-01)
Wu, AT
;
Liu, WD
;
Chung, WS
;
應用化學系
;
Department of Applied Chemistry
Sealed tube reactions of the naphthosultine 8 with a series of electron-deficient dienophiles (fumaronitrile, N-phenylmaleimide, dimethyl fumarate, and dimethyl acetylenedicarboxylate) in toluene at 180 degreesC gave corresponding 1:1 cycloadducts 11-14 in various amounts along with rearranged naphthosulfolene 7 in 67-95% yields. The reaction of 1,2,4,5-tetra(bromomethyl)benzene with Rongalite (sodium formaldehyde sulfoxylate) and tetrabutylammonium bromide in DMF gave benzodisultines 17 and 18 in a combined yield of 56%. Sealed tube reactions of benzodisultines 17 and 18 with a series of dienophiles in xylene at 200 degreesC gave corresponding 1:1 and 1:2 cycloadducts 20-27. The results suggested that thermal extrusion of sulfur dioxide from these sultines led to either o-naphthoquinodimethane 6 (from 8) or bis-o-quinodimethane 19 (from 17 and 18); subsequent trapping of these reactive intermediates by dienophiles and SO2 gave various 1:1 and 1:2 Diels-Alder adducts in modest to excellent yields.