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1.
Roshantha A.S. Chandraratna Robert R. Birge William H. Okamura 《Tetrahedron letters》1984,25(10):1007-1010
The electronic absorption spectra of the four new 12---locked retinals (1a–1d) bearing 7-, 11- double bond geometries are described and compared with those of analogous 7-, 11--geometries (1e–1h) and parent retinals (2a-h). 相似文献
2.
Cycloaddition reactions between vinyl ethers 3 and -quinone methides 2, thermally generated from 2-hydroxybenzyl alcohols 1, have been studied. The structure and conformational preferences of the 4-substituted 2-ethoxy-(2,3)-dihydro-2-benzopyrans 4–9 obtained, which show new interesting features, are discussed together with competitive kinetic data. The cycloaddition process is concerted and involves -quinone methides in the -configuration. The OEt- transition state seems to be preferred with ethyl vinyl ether and -1-propenyl ethyl ether, whereas with -1-propenyl ethyl ether the stereoselectivity of the cycloaddition process depends on substituents on the methylene group of the starting alcohol 1. These results are discussed in terms of and preference of the propenyl ether methyl group. 相似文献
3.
O.R. Martin 《Tetrahedron letters》1985,26(17):2055-2058
Upon treatment with tin(IV) chloride, perbenzylated glycofuranosyl acetates such as 3 or 6 undergo an unusual, intramolecular α--arylation resulting from the internal Friedel-Crafts alkylation of the 2--benzyl substituent. 相似文献
4.
Shinichi Uesato Shinichi Ueda Koji Kobayashi Masao Miyauchi Hiroyuki Inouye 《Tetrahedron letters》1984,25(5):573-576
Administration of 2H- or 13C-labeled monoterpenes to f. cell suspension cultures demonstrated that iridoid glucosides of the suspension cultures are biosynthesized, after iridodial cation formation from 10-oxocitral (3), via 8-epiiridodial (13), 8-epiiridotrial (14), boschnaloside (8-epiiridotrial glucoside) (12) and dehydroiridotrial glucoside (8). In addition, the coexistence of a route via iridodial cation (4), dehydroiridodial (6), dehydroiridotrial (15) and dehydroiridotrial glucoside (8) is conceivable. 相似文献
5.
A stereoselectivity in an intramolecular cycloaddition of the olefinic -quinodimethanes 13 and 23 generated from the thermolysis of optically active 4β-[2-(4-methoxybenzocyclobutenyl)ethyl] -5α-methoxymethyl-3-phenyl-thio-methylenefuran-2-ones 12 and 22, respectively, is studied and a stereoselective synthesis of (+)--4,5-( 4-methoxybenzo) -1β,7aβ-(2α-methoxymethyl-5-oxofuro)hydrindane 1 is also described. 相似文献
6.
The structure of nigellicine (1) , an unusual alkaloid from the seeds of , was determined by x-ray diffraction and spectroscopic techniques. 相似文献
7.
Masaaki Yoshifuji Kozo Toyota Naoki Inamoto Ken Hirotsu Taiichi Higuchi 《Tetrahedron letters》1985,26(52):6443-6446
The sterically protected -phosphaethylene, -2-phenyl-1-(2,4,6-tri-t-butylphenyl)phosphaethylene (1-Z), was analyzed by X-ray crystallography. 相似文献
8.
A facile transformation of bicyclic keto esters to bisprotected (±)-8-epithienamycin enol activation
A facile “one-pot” transformation of bicyclic keto ester (2) to bisprotected (±)-8-epithienamycin enol phosphate activation followed by the addition-elimination reaction of -protected cysteamine derivative is described. 相似文献
9.
Yoshitsugu Arai Shū-ichi Kuwayama Yoshio Takeuchi Toru Koizumi 《Tetrahedron letters》1985,26(50):6205-6208
The Diels-Alder reaction of a novel chiral dienophile, alkyl ()-2--tolylsulfinylacrylates 1 with anthracene and cyclopentadiene showed high diastereoselectivity under the chelation controlled condition. 相似文献
10.
The indolization of deoxybenzoin ,, (Me, MeO, Cl), -NO2 and -EtO-phenylhydrazones (1) by the above reaction has been examined. All the reactions are carried out at room temperature and high yields of the corresponding indoles (2) are obtained even when -NO2 substituent is present. In this case longer reaction time is necessary. Alkoxyphenylhydrazones give the corresponding indoles (2) in high yields without showing collateral reactions which indeed are present in several Fischer routes on these derivatives. -Substituted phenylhydrazones (1) give a mixture of 4- and 6-substituted indoles in which the 6-isomer is always prevalent, a feature not inherent in the Fischer reactions. The regioselectivity is enhanced by the substituent steric hindrance increasing. The reaction can be also carried out at 0°C with a further improvement of its regioselectivity. 相似文献
11.
The kinetics of the homopolymerizations of styrene, N-(3-dimethylaminophenyl) maleimide (I) and N-(3-dimethylamino-6-methylphenyl) maleimide (II) in benzene and dimethylformamide, and the molecular weights of the polymers were studied. N-(3-Dimethylaminophenyl) succinimide, regarded as a model for polymer I, did not affect the polymerization of styrene. The data indicate degradative transfer of polymer radicals to dimethylformamide and pronounced transfer to monomers I and II (CM ≈ 0.06–0.07). The value of for II is 0.09 . 相似文献
12.
The efficient degradation of to the α-methylene ketone is described. Compound was then converted to the allylic alcohol - the precursor of vitamin D3 relatives. 相似文献
13.
The pigment complex from Flavobacterium spec strain C consists of pigments 1a to 1d whose isolation and structure elucidations are reported. These pigments exclusively belong to the new class of flexirubin type pigments. Up to now, pigments of this type have been found in gliding bacteria only. 相似文献
14.
Charles D. Hufford Babajide Oguntimein Michael Martin Jon Clardy 《Tetrahedron letters》1984,25(4):371-374
The isolation and structure determination of syncarpurea (1), a novel urea from is reported. 相似文献
15.
The unsaturated ketones 1 – 10 were protonated at low temperatures and studied by dynamic 13C NMR spectroscopy. Four interconverting stereoisomers were detected which differ in their conformation with respect to the CO and CC (enone) single bond. 相似文献
16.
Jan A. Glinski Balawant S. Joshi Szu-yinq Chen S.William Pelletier 《Tetrahedron letters》1984,25(12):1211-1214
A novel C19-diterpenoid alkaloid designated as tatsinine has been isolated from the roots of and its structure (3) has been derived from 1H NMR and 13C NMR spectroscopic evidence. 相似文献
17.
Lithiation of both ()- and ()-3-trimethylsilyl-2-propenyl ,-diisopropyl carbamate 2 affords the (2) -lithium compound 3. Aluminium- or titanium-mediated addition to aldehydes, 4 gives (1)-(3*4*)-enol carbamates 7. A stereospecific Peterson elimination (borontriflouride- or base-mediated) introduces the second double bond either with (3)- or with (3)-configuration. So just by reagent selection for each of the two steps, (1,3)-, (1,3)-, (1,3)-, or (1,3)- dienes 8 - 11, respectively, are prepared with stereoselectivities up to > 99.7% 相似文献
18.
Methods were developed to prepare 1 -methyl-, 3-methyl- and 4-0-methyl-ψ-isocytidine by selective methylation.35O-Tetraisopropyldisiloxanyl-ψ isocytidine (8) was trimethylsilylated and then treated with MeI and, after deprotection, 1 -methyl-ψ isocytidine (6) was obtained. The 2deoxy analog (7) was also prepared in a similar manner from the 2deoxy analog (10) of 8. Treatment of 8 with CH2N2 afforded the 3-methyl-ψ-isocytidine derivative (19) as the major product. Methylation with diazomethane also occurred mainly on N3 of the 2deoxy analog 10 to form 20. Removal of the 3 5O-protecting group from 19 and 20 afforded 3-methyl-ψ-isocytidine (14) and its 2-deoxy analog (15), respectively. 2-N-Acetyl- 35O-tetraisopropyldisiloxanyl-ψ-isocytidine (24), on the other hand, gave the 4-O-methyl derivative (25) as the major product upon CH2N2 treatment. Subsequent deprotection of 25 afforded 4-O-methyl-ψ-isocytidine (29). aiv51b1p33b 相似文献
19.
Hideo Nemoto Mitsuo Nagai Keiichiro Fukumoto Tetsuji Kametani 《Tetrahedron letters》1985,26(38):4613-4616
A stereoselective total synthesis of 19-nor-Δ9(10)-progesterone (14) was achieved through des-A B-aromatic steroid (3) which was obtained by an intramolecular cycloaddition of the -quinodimethane generated from the thermolysis of 3-isopropenyl-5-(4-metho-xybenzocyclobutenyl)pentan-2-one-2-ethylene ketal (2), and the compound (14) thus obtained was further converted into Δ9-progesterone (18). 相似文献
20.
Contrary to the recent work of J. M. Thomas et al. (J. Chem. Soc. Chem. Commun., 678, 1981), it was found that a high-resolution neutron powder diffraction pattern of a sample of dehydrated Na zeolite A (with ratio 1.09) can be indexed and refined in the cubic groups (A. K. Cheetham and J. C. Taylor, J. Solid State Chem.21, 253, 1977) and , whereas in the rhombohedral space group refinement was unsuccessful. For two other samples having ratios of 1.03 and 1.12 the diffraction patterns again showed no evidence of rhombohedral distortion and can be indexed using a cubic unit cell. It appears that the Si, Al ordering of zeolite A, and hence the crystal symmetry, must depend upon the conditions of preparation of the zeolite. 相似文献