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- Olsson, Roger, et al.
(författare)
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Endocyclic cleavage of glycosides. VI. Substituent effects of the alkylative endocyclic cleavage of glycosides
- 1998
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Ingår i: Tetrahedron. - 0040-4020. ; 54:15, s. 3935-3954
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Tidskriftsartikel (refereegranskat)abstract
- A number of pentopyranoside derivatives were treated with Me 3 Al in order to investigate the influence of structural parameters on the methyl group transfer in the endocyclic alkylative cleavage reaction of these substrates. A cyclic CH ··· O hydrogen bonded model is suggested as an intermediate, which is used to explain the stereoselectivities for different substrates. In several, cases the diastereoselectivities were better than 9:1.
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- Tsirk, Anders, et al.
(författare)
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Synthesis of Substituted Benzo[b]indolizidines and Benzo[b]quinolizidines via Ring-Opening of 3-Bromo-2,5-dimethylthiophene-1,1-dioxide
- 1997
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Ingår i: Tetrahedron. - 0040-4020. ; 53:2, s. 771-784
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Tidskriftsartikel (refereegranskat)abstract
- A new method for the preparation of benzo[b]indolizidines and benzo[b]quinolizidines based on two reactions: an amine induced ring-opening of 3-bromo-2,5-dimethylthiophene-1,1-dioxide (1) with 2-allyl-pyrrolidine (2), 2-allylpiperidine (3), 2-[2-(1',3'-dithiolan)methyl]pyrrolidine (4) and 2-[2-(1'-3'-dithiolan)methyl]piperidine (5); and an intramolecular Diels-Alder reaction, is described. Copyright (C) 1996 Elsevier Science Ltd
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- Garg, Neeraj, et al.
(författare)
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Preparation of cis-5-methoxy-and-7-methoxy-1-acetoxy-1,2,3,4,4a,10a-hexahydro-9(10H)-phenanthrenone. An epoxide-arene reaction involving a selective 1,2-alkyl shift rearrangement
- 1996
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 52:48, s. 15209-15224
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Tidskriftsartikel (refereegranskat)abstract
- The preparation of cis-1α-acetoxy-7-methoxy-1,2,3,4,4a,10a-hexahydro-9(10H)- phenanthrenone 5 was accomplished starting from 6-methoxy-1-tetralone. Reduction of 7-methoxy-1,2,3, 4,9,10-hexahydro-1-oxo-phenanthrene 8, acetylation and subsequent oxidation delivered 5. Application of an analogus procedure to the preparation of cis-1β-acetoxy-5-methoxy-1,2,3,4,,4a,10a-hexahydro-9(10H)- phenanthrenone 6 was not feasible. A more elaborate route was developed for the synthesis of compound 6, where an epoxide-arene reaction involving a 1,2-alkyl shift rearrangement, constituted a highly selective key transformation. The compounds 5 and 6 were prepared. A route was developed for the synthesis of compound 6, where an epoxide-arene reaction involving a 1,2-alkyl shift rearrangement, constituted a highly selective key transformation.
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- Laglet, Abraham, et al.
(författare)
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Synthesis and Reactions of 1,1-dinitro-2,2-dinitroethylene
- 1998
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Ingår i: Tetrahedron. - 0040-4020 .- 1464-5416. ; 54:38, s. 11525-11536
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Tidskriftsartikel (refereegranskat)abstract
- Low temperature nitrations of 2-methylimidazole gave in addition to the known 2-methyl-5(4)-nitroimidazole (1), 2-(dinitromethylene)-5,5-dinitro-4-imidazolidinone (3) and parabanic acid (2). The tetranitro compound 3 was also obtained by nitration of 2-methyl-4,5-dihydro-(1H)-5-imidazolone (8). Thermal decomposition of 3 gave 2-(dinitromethylene)-4,5-imidazolidinedione (4) which also was the product from nitration of the new compound 2-methoxy-2-methyl-4,5-imidazolidinedione. Treatment of 4 with aqueous ammonia gave the previously unknown 1,1-diamino-2,2-dinitroethylene (5). The physical properties and chemical behaviour of (5) are described.
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14. |
- Marton, J., et al.
(författare)
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Reaction of morphinan-6,8-dienes with azadienophiles
- 1996
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 52:7, s. 2449-2464
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Tidskriftsartikel (refereegranskat)abstract
- Reaction of various morphinan dienes, i.e. thebaine (1a), N-demethyl-N-formylthebaine (1b), 6-demethoxythebaine (1c), β-dihydrothebaine (2a), 4-acetoxy-β-dihydrothebaine (2b), 7-chloro-6-demethoxythebaine (3a) and 7-bromo-6-demethyoxythebaine (3b) with 4-phenyl-4H-1,2,4-triazoline-3,5-dione (PTAD) gave rise to new Diels-Alder (DA) adducts. DA-reaction of 1a, 1b and 1c with PTAD led to the products of the β-face attack of the dienophile at the diene unit. The W coupling (4J(5β,18)) in the 1H-NMR spectra was indicative of these structures. α-Face addition took place in the case of morphinan dienes with opened ring E, and a by-product was formed due to the S(E) reaction of PTAD with the adducts. The structure of these derivatives was confirmed by means of NMR spectroscopic methods. The retro Diels-Alder (rDA) reaction of the adducts 4a and 4b readily took place in polar-aprotic solvents in the presence of bases with low nucleophilic character.
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15. |
- Marton, J., et al.
(författare)
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Studies on the synthesis of β-thevinone derivatives
- 1998
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Ingår i: Tetrahedron. - : Elsevier BV. - 0040-4020 .- 1464-5416. ; 54:31, s. 9143-9152
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Tidskriftsartikel (refereegranskat)abstract
- The reactions of β-thevinone and β-dihydrothevinone with tert- butylmagnesium chloride and n-propylmagnesium bromide were investigated. Further chemical transformations (N-demethylation, N-alkylation, O- demethylation) of the tertiary alcohols afforded the known β-buprenorphine and the hitherto unknown β-etorphine and β-dihydroetorphine. The by- products of these reactions were also isolated, their structures identified, and the mode of their formation was explained.
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- Tholander, J, et al.
(författare)
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Syntheses of 6,12-disubstituted 5,11-dihydroindolo[3,2-b]carbazoles, including 5,11-dihydroindolo[3,2-b]carbazole-6,12-dicarbaldehyde, an extremely efficient ligand for the TCDD (Ah) receptor
- 1999
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Ingår i: TETRAHEDRON. - 0040-4020. ; 55:43, s. 12577-12594
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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- FOLDESI, A, et al.
(författare)
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PARTIALLY-DEUTERATED NUCLEOTIDE RESIDUES IN LARGE DNA DUPLEX SIMPLIFY THE SPECTRAL OVERLAP AND PROVIDE BOTH THE J-COUPLING AND NOE INFORMATIONS BY THE NMR-WINDOW APPROACH
- 1995
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Ingår i: TETRAHEDRON. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020. ; 51:36, s. 10065-10092
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The nucleobase-protected partially-deuterated 5'-O-DMTr-2'(#),2 ''(#)3',4'(#),5',5 ''-H-2(5)-2'-deoxyribonucleoside 3'-phosphoramidite phosphoramidite derivatives 17a,b - 20a,b, containing C2' isotopomeric mixture of deuterons and protons [similar to 15 a
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- Luyten, I, et al.
(författare)
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Determination of the ionization constants of C-nucleosides
- 1997
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Ingår i: TETRAHEDRON. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020. ; 53:20, s. 6903-6906
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We here report for the first time the ionization constant of 9-deazaadenosine (1) (pK(a) 6.0) as well as the third ionization constant for Formycin B (2) (pK(a) of 1.3) in addition to its two known pK(a)s of 8.8 and 10.4. (C) 1997 Elsevier Science Ltd.
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28. |
- PAPCHIKHIN, A, et al.
(författare)
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THE DIASTEREOSPECIFIC SYNTHESIS OF NEW 2',3'-CIS-ALPHA-FUSED CARBOCYCLIC NUCLEOSIDES
- 1995
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Ingår i: TETRAHEDRON. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020. ; 51:1, s. 329-342
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The first diastereospecific synthesis of [3.3.0]- and [3.4.0]-alpha-cis-fused-carbocyclic nucleosides 10, 12 and 20, starting directly from 2'-O-(TBDMS) or 3'-O-(TBDMS) derivatives of 5'-O-MMTr-2',3'-seco-ribo-thymidines, 1 and 13 (ref. 4), have been repo
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33. |
- PURI, N, et al.
(författare)
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THE SYNTHESIS AND REACTIVITY OF NEW 2-(N,N-DIISOPROPYLAMINO)-3-METHYLSULFONYL-1,3,2-BENZOXAZAPHOSPHOLES - THE UTILITY OF THE 5-CHLORO ANALOG IN THE ONE-POT SYNTHESIS OF OLIGOTHIOPHOSPHATES - [AP(S)PPA, AP(S)PPPA, PPP5'A2'P(S)5'A, M(7)GP(S)PPA, AP(S)PPPP
- 1995
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Ingår i: TETRAHEDRON. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020. ; 51:10, s. 2991-3014
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The synthesis of 2-(N,N-diisopropylamino)-2-3-dihydro-3-methylsulfonyl-1,3,2- benzoxazaphospholes 22, 23 and 24 is reported. Their reactivities have been investigated using a variety of acid catalyst under conditions normally employed in phosphoramidite c
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37. |
- Trifonova, A, et al.
(författare)
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Diastereospecific chemical synthesis of ribonucleosides-3 ',4 ',5 ',5 ''-d(4)
- 1999
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Ingår i: TETRAHEDRON. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0040-4020. ; 55:15, s. 4747-4762
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The diastereospecific chemical syntheses of uridine-3',4',5',5"-d(4), cylidine-3',4',5',5''-d(4), adenosine-3',4',5',5"-d4 and guanosine-3',4',5',5"-d(4) (>97 atom % H-2 at C3', C4' and C5') have been achieved by condensation of appropriately protected ag
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