| 1. |
- Baeckstroem, P., et al.
(författare)
-
Convenient Method for the Synthesis of Lineatin, a Pheromone Component of Trypodendron-Lineatum
- 1991
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 56:10, s. 3358-3362
-
Tidskriftsartikel (refereegranskat)abstract
- Synthesis of racemic lineatin (1), a pheromone component of Trypodendron lineatum, is described. Condensation of 5-methyl-5-hexen-2-one (2) and triethyl phosphonoacetate with LiN(SiMe3)2 gave esters 3, which upon hydrolysis gave acids 4a-f. The bicyclo[3.2.0] ring compounds 5 and 6 were obtained via an intramolecular [2 + 2] addition by refluxing underivatized carboxylic acids 4a-f with NaOAc and Ac2O. Compound 5 was isomerized to the thermodynamically more stable isomer 6 using a Pd/C catalyst activated with hydrogen. Reduction of 6 with LiAlH4 gave the endo and exo isomers 7a and 7b (4:1). Isolation of the alcohol 7a followed by acetylation gave 8. Subsequent oxidation with OsO4 and methylmorpholine N-oxide gave diol 9. Cleavage of 9 with H5IO6 in diethyl ether gave keto aldehyde 10, which was converted to keto acetal 11. Treatment of 11 with MeMgBr followed by acidic workup gave 1. The overall efficiency is approximately 20%.
|
|
| 2. |
|
|
| 3. |
- Brinck, Tore, Professor, 1965-, et al.
(författare)
-
Octanol Water Partition-Coefficients Expressed In Terms Of Solute Molecular-Surface Areas And Electrostatic Potentials
- 1993
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 58:25, s. 7070-7073
-
Tidskriftsartikel (refereegranskat)abstract
- For 70 molecules of various types and sizes, it is shown that their experimental octanol/water partition coefficients can be represented quantitatively in terms of the solute's molecular surface area in conjunction with two statistically-based quantities calculated from its surface electrostatic potential; the latter are the average deviation of the potential and its total variance. An ab initio SCF approach was used to compute STO-3G*-optimized geometries and STO-5G* electrostatic potentials.
|
|
| 4. |
- BRINCK, T, et al.
(författare)
-
RELATIONSHIPS BETWEEN THE AQUEOUS ACIDITIES OF SOME CARBON, OXYGEN, AND NITROGEN ACIDS AND THE CALCULATED SURFACE LOCAL IONIZATION ENERGIES OF THEIR CONJUGATE BASES
- 1991
-
Ingår i: Journal of Organic Chemistry. - UNIV NEW ORLEANS,DEPT CHEM,NEW ORLEANS,LA 70148. : AMER CHEMICAL SOC. - 0022-3263 .- 1520-6904. ; 56:17, s. 5012-5015
-
Tidskriftsartikel (refereegranskat)abstract
- Average local ionization energies (IBAR(r)) have been computed on the molecular surfaces of the conjugate bases for four different groups of carbon and oxygen acids using an ab initio self-consistent-field molecular orbital approach. The lowest surface IBAR(r) (IBAR(S,min)) are generally found on the atom from which the proton has been abstracted. Good linear relationships between aqueous acidities and IBAR(S,min) are found for the different groups. A single linear relationship between pK(a) and IBAR(S,min) that includes the four groups and three additional nitrogen acids also exists; the correlation coefficient is 0.97. This provides a means for predicting the pK(a)'s of a large variety of carbon, oxygen, and nitrogen acids.
|
|
| 5. |
- Bäckvall, Jan-E., et al.
(författare)
-
Stereocontrolled Lactonization Reactions via Palladium-Catalyzed 1,4-Addittion to Conjugated Dienes
- 1993
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 58:20, s. 5445-5451
-
Tidskriftsartikel (refereegranskat)abstract
- Stereocontrolledp alladium(I1)-catalyzed1 ,4-chloro-and 1,4-acetoxylactonizations o f conjugated cyclic dienes have been developed to give stereodefined fused lactones. The stereochemistry of the 1,4- acetoxylactonization was controlled by the ligand on the metal catalyst, and in this way either a cisor truns-acetoxylactonization was obtained. This dual stereoselectivity is explained by a stereocontrolled acetate attack (trans or cis, respectively) on the allyl group in the catalytic (π-allyl)- palladium intermediate. To further strengthen the mechanism the intermediate (π-ally1)palladium complex was isolated and fully characterized. A stereospecific synthesis of cis- and truns-2-[6- (benzyloxy)-2,4-heptadien-l-yllacetic a cid (cis- and truns-9) followed by stereoselective Pd(I1)- catalyzed chloro- and acetoxylactonization in acetonelacetic acid resulted in highly functionalized fused lactones with control of the relative stereochemistry at four different carbons.
|
|
| 6. |
- Bäckvall, Jan-Erling, et al.
(författare)
-
Syntheses of (±)-α- and (±)- γ- Lycorane via a Stereocontrolled Organopalladium Route
- 1991
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 56:9, s. 2988-2993
-
Tidskriftsartikel (refereegranskat)abstract
- Total syntheses of (+/-)-alpha-and (+/-)-gamma-lycorane are described. The key steps in the syntheses are the stereocontrolled palladium-catalyzed intramolecular 1,4-chloroamidation of 12 to 13 and the subsequent anti-stereoselective copper-catalyzed S(N)2' reaction of allylic chloride 13 with [3,4-(methylenedioxy)phenyl]magnesium bromide to give 14. Hexahydroindole 14 has the required relative stereochemistry between carbons 3a, 7, and 7a for alpha-lycorane (1a) and was transformed to the latter via 15 and 16. The epimeric gamma-lycorane (2) was obtained by performing the Bischler-Napieralski cyclization on 14, which led to a highly stereoselective isomerization to give exclusively 17. Compound 17 was subsequently transformed to 2. The overall yield from ester 8 to (+/-)-alpha- and (+/-)-gamma-lycorane was 40 and 36%, respectively.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Magnusson, Göran, et al.
(författare)
-
Prespacer Glycosides in Glycoconjugate Chemistry. Dibromoisobutyl (DIB) Glycosides for the Synthesis of Neoglycolipids, Neoglycoproteins, Neoglycoparticles, and Soluble Glycosides
- 1990
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 55:12, s. 3932-3946
-
Tidskriftsartikel (refereegranskat)abstract
- 3-Bromo-2-(bromomethyl)propyl (dibromoisobutyl or DIB) mono- to tetrasaccharide glycosides were prepared in moderate to high yields by treatment of the corresponding 1-0-acetyl saccharides with 3-bromo-2-(bromo-methyl)propanol (DIBOL) and boron trifluoride etherate. Treatment of the DIB glycosides with alkyl- and ω-methoxycarbonylalkyl thiols gave the corresponding bis-sulfide glycolipids and spacer arm sugars, respectively. Oxidation of the sulfides with m-chloroperbenzoic acid gave the corresponding bis-sulfones. Treatment of the DIB glycosides with tetrabutylammonium fluoride gave the corresponding allylic bromide glycosides, and addition of thiols gave the allylic sulfides. Prolonged fluoride treatment gave the allylic fluorides. Hydrogenation of DIB glycosides under basic conditions gave the corresponding isobutyl glycosides. Spacer arm and allylic bromide glycosides were coupled to bovine serum albumin and derivatized silica gel, thereby providing artificial glycoprothins and glycoparticles.
|
|
| 10. |
|
|
| 11. |
- Rehnberg, Nicola, et al.
(författare)
-
Carbohydrate-Derived Chiral Furanosidic α,β-Unsaturated Aldehydes in Conjugate and Diels-Alder Addition Reactions. Steric Hindrance by the Anomeric Substituent
- 1990
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 55:20, s. 5477-5483
-
Tidskriftsartikel (refereegranskat)abstract
- The title aldehydes (lr, 1s, 2, and 3) underwent virtually diastereospecific conjugate addition by lithium methylcyanocuprate. The bulkiness of the anomeric benzyloxy or methoxy groups direct the attacking nucleophile to the less hindered side of the furanosidic ring. The stereochemical outcome of the Diels-Alder additions of cyclopentadiene to lr and 1s was governed almost completely by the bulkiness of the anomeric benzyloxy group, which directed cyclopentadiene to the less hindered side of the furanosidic ring. When an additional substituent was positioned trans to the anomeric substituent (2), a mixture of all four possible diastereomers was obtained. With both substituents on the same side of the ring (3), complete π-facial selectivity was obtained. In both the conjugate and Diels-Alder addition products, NMR data could be used to determine the stereostructures of all diastereomers. Both product types showed oxygen atom induced proton deshielding and carbon shielding effects in NMR.
|
|
| 12. |
- Rehnberg, Nicola, et al.
(författare)
-
Chiral Aldehydes by Ring Contraction of Pento- and Hexopyranoside Epoxides
- 1990
-
Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 55:20, s. 5467-5476
-
Tidskriftsartikel (refereegranskat)abstract
- The chiral aldehydes (-)-(2S,5S)- and (-)-(2S,5R)-2-[[[dimethyl( 1,1,2-trimethylpropyl)silyl]oxy]methyl]-5-methoxy-2,5-dihydrofuran-3-carbaldehyde (2 and 4) were synthesized in 60 and 15% yield, respectively, by lithium bromide induced rearrangement of 6-O-silylated methyl 2,3- and 3,4-anhydro-a- and -d-D-hexopyranosides, obtained in two steps from methyl α- and β-D-glucopyranoside. Rearrangement of various other pento- and hexoside epoxides permitted the suggestion of probable reaction routes. Hydrogenation of the unsaturated aldehydes gave the corresponding saturated aldehydes in good yield.
|
|
| 13. |
|
|
| 14. |
|
|
