Browsing by Author "Chern, JH"

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A novel hydride rearrangement of the acetal group of tetraacetal tetraoxa-cages mediated by Lewis acids
(1997-03-21)
Wu, HJ
;
Chern, JH
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
Treatment of tetraoxa-cages 1a-f with Lewis acids such as TlC4, AlCl3, BF3 . OEt(2) and MeSO(3)H in dichloromethane at 25 degrees C gives the rearrangement products 2a-f in 90% yields regioselectively and stereoselectively; a novel hydride rearrangement of the acetal group of tetraacetal tetraoxa-cages mediated by Lewis acids.
A novel hydride rearrangement of the acetal group of tetraacetal tetraoxa-cages mediated by Lewis acids
(1997-03-21)
Wu, HJ
;
Chern, JH
;
應用化學系
;
Department of Applied Chemistry
Treatment of tetraoxa-cages 1a-f with Lewis acids such as TlC4, AlCl3, BF3 . OEt(2) and MeSO(3)H in dichloromethane at 25 degrees C gives the rearrangement products 2a-f in 90% yields regioselectively and stereoselectively; a novel hydride rearrangement of the acetal group of tetraacetal tetraoxa-cages mediated by Lewis acids.
A novel one-pot conversion of tetraacetal tetraoxa-cages to aza-cages mediated by iodotrimethylsilane in acetonitrile
(1997-04-21)
Wu, HJ
;
Chern, JH
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
Treatment of the tetraacetal tetraoxa-cages 1a-f with excess of iodotrimethylsilane in acetonitrile at 25 degrees C gave the novel tetraacetal trioxamonoaza-cages 2a-f in 75-80% yields respectively, a novel one-pot conversion of era-cages to ata-cages. (C) 1997 Elsevier Science Ltd.
A novel one-pot conversion of tetraacetal tetraoxa-cages to aza-cages mediated by iodotrimethylsilane in acetonitrile
(1997-04-21)
Wu, HJ
;
Chern, JH
;
應用化學系
;
Department of Applied Chemistry
Treatment of the tetraacetal tetraoxa-cages 1a-f with excess of iodotrimethylsilane in acetonitrile at 25 degrees C gave the novel tetraacetal trioxamonoaza-cages 2a-f in 75-80% yields respectively, a novel one-pot conversion of era-cages to ata-cages. (C) 1997 Elsevier Science Ltd.
A remarkable effect of C-O-C bond angle strain on the regioselective double nucleophilic substitution of the acetal group of tetraacetal tetraoxa-cages and a novel hydride rearrangement of tetraoxa-cages
(1997-05-16)
Wu, HJ
;
Chern, JH
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
A remarkable effect of C-O-C bond angle strain on the regioselective double nucleophilic substitution of the acetal group of tetraacetal tetraoxa-cages and a novel regioselective and stereoselective hydride rearrangement of tetraoxa-cages are reported. Reaction of the tetraacetal tetraoxa-cages 1 with 3 equiv of triethylsilane (at -78 degrees C), cyanotrimethylsilane (at 25 degrees C), and allyltrimethylsilane (at -78 degrees C) in dichloromethane in the presence of TiCl4 gave the double nucleophilic substitution products 2, 6, and 7 in 85-90% yields, respectively. No detectable amount of other regioisomers was obtained. Reaction of 1a with (methylthio)trimethylsilane and (phenylthio)trimethylsilane in dichloromethane in the presence of TiCl4 at -78 degrees C gave the symmetric products 10a,b and the unsymmetric products 11a,b in ratios of 8-10:1. The stereochemistry of the symmetric substitution products was proven by X-ray analysis of the crystalline compound 10a. The mechanism of the double nucleophilic substitution of the tetraoxa-cages 1 are discussed. Treatment of the tetraoxa-cages 1a,c and 22a-c with 2 equiv of TiCl4 or MeSO3H in dichloromethane at 25 degrees C for 3 h regioselectively and stereoselectively gave the novel hydride rearrangement products 16a,b and 23a-c respectively. No detectable amount of other regioisomers was observed. The stereochemistry of the hydride rearrangement was proven by DIBAL-H reduction of 16 and 23 and X-ray analysis of the reduction product 24a. We attribute the high regioselectivity of the double nucleophilic substitution and the hydride rearrangement of the tetraoxa-cages 1 to the bond angle strain of the unusually large bond angle of C(3)-O(4)-C(5) of the tetraoxa-cages.
Chemical transformation of tetraacetal tetraoxa-cages to aza-cages and amido-cages mediated by iodotrimethylsilane and the combination of chlorotrimethylsilane and sodium iodide in nitriles
(1998-05-28)
Chern, JH
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Wu, HJ
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應用化學系
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Department of Applied Chemistry
An one-pot conversion of tetraacetal tetraoxa-cages la-e to aza-cages 2a-e mediated by iodotrimethylsilane in alkyl nitriles at 25 degrees C via the ring expansion compound 9 as the reaction intermediate was discovered. A Ritter-type reaction was proposed for the mechanism of this conversion. On the other hand, reaction of tetraacetal tetraoxa-cages 1 with Me3SiCl and NaI in nitriles at 25 degrees C gave the amido-cages 12. Conjugated nitriles and Lewis acids, such as TiCl4 or BF3 . OEt2 were found to be ineffective for the conversion of era-cages to aza-cages. The structures of 2a and chemical transformation product 16 were proven by X-ray analysis. (C) 1998 Elsevier Science Ltd. All rights reserved.
Ozonolysis of 2-endo-7-anti-diacylnorbornenes. A new entry for the synthesis of 2,4,6,13-tetraoxapentacyclo[5.5.1.0(3,11).0(5,9).0(8,12)]tridecanes
(1997-02-17)
Wu, HJ
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Chern, JH
;
Wu, CY
;
交大名義發表
;
應用化學系
A new route for the synthesis of the title compounds 4a, 4b, 10a, and 10b has been developed via ozonolysis of 2-endo-7-anti-diacylnorbornenes 3a, 3b, 9a, and 9b. The synthesis of the unsubstituted (parent) compound 4a of tetraacetal tetraoxa-cages has been accomplished for the first time by this new entry. Ozonolysis reactions of 3a, 3b, and 9a were also performed in CDCl3 for understanding the final ozonide structures and the ozonation chemistry. Ozonolysis of 3a, 3b, and 9a in CH2Cl2 at -78 degrees C followed by treatment with triethylamine provided an indirect support for the structures of the final ozonides 11a, 11b, and 14. (C) 1997, Elsevier Science Ltd.
Synthesis of 4-oxo- and 4-anti-formyl-8,10,12,13-tetraoxapentacyclo[5.5.1.0(2,6).0(3,11).0(5,9)]tridecanes
(1997-12-29)
Wu, HJ
;
Chern, JH
;
應用化學系
;
Department of Applied Chemistry
The synthesis of 4-oxo- and 4-anti-formyl-8,10,12,13-tetraoxapentacyclo[5.5.1.0(2,6).0(3,11).0(5,9)]tridecanes has been accomplished. Ozonolysis of compounds 10a,b and 12a-c in dichloromethane at -78 degrees C followed by reduction with dimethyl sulfide gave the title compounds, 4-oxo-tetraoxa-cages 11a,b and 14a-c, in moderate yields. Ozonolysis of the endo-syn isomers 15a,b and 18a,b under the same reaction conditions gave 4-anti-formyl-tetraoxa-cages 17a,b and 20a,b, respectively. (C) 1997 Published by Elsevier Science Ltd.
Synthesis of 4-oxo- and 4-anti-formyl-8,10,12,13-tetraoxapentacyclo[5.5.1.0(2,6).0(3,11).0(5,9)]tridecanes
(1997-12-29)
Wu, HJ
;
Chern, JH
;
交大名義發表
;
應用化學系
;
National Chiao Tung University
The synthesis of 4-oxo- and 4-anti-formyl-8,10,12,13-tetraoxapentacyclo[5.5.1.0(2,6).0(3,11).0(5,9)]tridecanes has been accomplished. Ozonolysis of compounds 10a,b and 12a-c in dichloromethane at -78 degrees C followed by reduction with dimethyl sulfide gave the title compounds, 4-oxo-tetraoxa-cages 11a,b and 14a-c, in moderate yields. Ozonolysis of the endo-syn isomers 15a,b and 18a,b under the same reaction conditions gave 4-anti-formyl-tetraoxa-cages 17a,b and 20a,b, respectively. (C) 1997 Published by Elsevier Science Ltd.
Synthesis of carbon-chain tethered bistetraoxa-cage compounds
(1998-02-01)
Chern, JH
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Wu, HJ
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Wang, SL
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Liao, FL
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應用化學系
Carbon-chain tethered bistetraoxa-cage compounds 7a-c and 8a-c were synthesized from 2-methyl-furan in a four-step sequence. They were obtained from ozonolysis of the syn bisadducts 5a-c and the anti bisadducts 6a-c in dichloromethane at -78 degrees C followed by reduction with dimethyl sulfide. The structure of the anti bisadduct 6a was proven by X-ray crystallographical analysis.
Synthesis of diacetal trioxa-cage compounds via a sequential cyclization reaction of norbornene derivatives induced by electrophiles
(1997-09-05)
Wu, HJ
;
Tsai, SH
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Chern, JH
;
Lin, HC
;
應用化學系
The synthesis of diacetal trioxa-cage compounds via a sequential cyclization reaction of norbornene derivatives induced by electrophiles in a short sequence is reported. Treatment of the norbornene derivatives 2a-d and 10b with I-2 in aqueous THF in the presence of KI at 25 degrees C regioselectively gave the iodo-cage compounds 3a-d and 11 in 80-90% yields, respectively, via a iodine-induced sequential cyclization reaction. No detectable amount of other regioisomers or monocyclization products was obtained. The synthesis of triora-cages 14a-e was accomplished from 3a-d and 11 in a two-step sequence. Treatment of diacylnorbornenes 15a-f with I-2 in aqueous THF at 25 degrees C regioselectively and stereoselectively gave the sequential cyclization products 16a-f, respectively, which were converted in one step to the diacetal trioxa-cages 24a-f in high yields. The structure of these trioxa-cages was proven by X-ray analysis of the crystalline compound 14e. Other electrophiles, such as bromine, m-CPBA, and Hg(OAc)(2), were also found to be effective for the sequential cyclization reaction. Oxymercuration of 15a-f and 2a-c with Hg(OAc)(2) in aqueous THF followed by reduction with NaBH4 at 25 degrees C gave compounds 28a-f and 30b,d,c in high yields, respectively.
Synthesis of diacetal trioxa-cage compounds via a sequential cyclization reaction of norbornene derivatives induced by electrophiles
(1997-09-05)
Wu, HJ
;
Tsai, SH
;
Chern, JH
;
Lin, HC
;
交大名義發表
The synthesis of diacetal trioxa-cage compounds via a sequential cyclization reaction of norbornene derivatives induced by electrophiles in a short sequence is reported. Treatment of the norbornene derivatives 2a-d and 10b with I-2 in aqueous THF in the presence of KI at 25 degrees C regioselectively gave the iodo-cage compounds 3a-d and 11 in 80-90% yields, respectively, via a iodine-induced sequential cyclization reaction. No detectable amount of other regioisomers or monocyclization products was obtained. The synthesis of triora-cages 14a-e was accomplished from 3a-d and 11 in a two-step sequence. Treatment of diacylnorbornenes 15a-f with I-2 in aqueous THF at 25 degrees C regioselectively and stereoselectively gave the sequential cyclization products 16a-f, respectively, which were converted in one step to the diacetal trioxa-cages 24a-f in high yields. The structure of these trioxa-cages was proven by X-ray analysis of the crystalline compound 14e. Other electrophiles, such as bromine, m-CPBA, and Hg(OAc)(2), were also found to be effective for the sequential cyclization reaction. Oxymercuration of 15a-f and 2a-c with Hg(OAc)(2) in aqueous THF followed by reduction with NaBH4 at 25 degrees C gave compounds 28a-f and 30b,d,c in high yields, respectively.
Synthesis of tetraacetal tetraoxa-cage compounds with alkyl substituents at different sites of the oxa-cage skeleton
(1996-06-01)
Lin, RL
;
Wu, CY
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Chern, JH
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Wu, HJ
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應用化學系
Tetraacetal tetraoxa-cage compounds 3a, 3b, 4a, 4b, 7, 13, 14, and 15 were synthesized by a short sequence. They were obtained from ozonolysis of endo adducts 1a, 1b, 2a, 2b, and 6 in dichloromethane at -78 degrees C followed by reduction with dimethyl sulfide. Ozonolysis of 7-anti-trimethylsilyl-5,6-bis-endo-diacetylnorbornene 8 under the same reaction conditions did not give the tetraoxa-cage 9. The methylsulfinyl era-cage 13 derived from 1-methylthio-5,6-bis-endo-diacetylnorbornene 11 was converted to com pounds 14 and 15.