Browsing by Author "Pai, IF"

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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.
Thermal and microwave assisted reactions of 2,5-disubstituted thienosultines with [60]fullerene: non-Kekule biradicals and self-sensitized oxygenation of the cycloadduct
(2004-11-22)
Chi, CC
;
Pai, IF
;
Chung, WS
;
應用化學系
;
Department of Applied Chemistry
Refluxing an o-dichlorobenzene solution of 2,5-disubstituted thienosultines 10a-f with [60]fullerene for 2-24 h gave both 1:1 and 2:1 cycloadducts in 37-79% isolated yields. The reaction was highly accelerated by microwave irradiation giving comparable yields of cycloadducts. Sultines 10a-f underwent cheletropic extrusion of SO2 to form the corresponding non-Kekule biradical intermediates 11a-f, which were subsequently trapped by [60]fullerene to form corresponding cycloadducts. The activation energy barriers (DeltaG(c)(not equal)) determined for the boat-to-boat inversion of these 4',5',6',7'-tetrahydrobenzo[c]thieno-[5',6':1,2][60]fullerene adducts 12a-f were found to be in the range of 13.5-14.8 kcal/mol. Unexpectedly, one of the monoadduct 12a was found to be labile when kept in air under ambient light. Two new products 15 (a sulfine-enone) and 16 (an endione) were isolated from the decomposed 12a and were found to derive from self-sensitized singlet oxygen reaction on the 2,5-dimethylthieno moiety of 12a. (C) 2004 Elsevier Ltd. All rights reserved.