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[reaction: see text] Transmetalation of tin-bearing cyclic imidates gave 2-azaallyllithiums that underwent [pi6s + pi4s] cycloadditions with cycloheptatriene to produce tricyclic adducts, which may be useful as analogs of cocaine. The peri- and stereoselectivity of this process are discussed.
[reaction: see text] The stereoselective synthesis of novel alpha-epoxy-beta-amino acids is described by a route that combines the chemistry of oxazolinyloxiranyllithiums with that of nitrones. The intermediate trioxadiazadispiro[2.0.4.3]undecanes 4 have been isolated and converted by hydrolysis into epoxy-5-isoxazolidinones 5 which can be transformed into the alpha-epoxy-beta-amino acids 8 by N-O reduction.
[reactions: see text] A concise synthesis of highly functionalized cyclopentane derivatives via a Brook rearrangement mediated stereoselective linchpin cyclization reaction involving tert-butyldimethylsilyl-1,3-dithianyllithium and homochiral 1,4-bis-epoxides is described.
Reductions of several types of compounds with lithium and ethylenediamine using low molecular weight amines as solvent are described. In all cases 1 mol of ethylenediamine or N, N'-dimethylethylenediamine per gram-atom of lithium was used. In some cases it was beneficial to add an alcohol as a proton donor. These reaction conditions were applied to the debenzylation of N-benzylamide and lactams which are refractory to hydrogenolysis with hydrogen and a catalyst. N-Benzylpilolactam 2, synthesized from pilocarpine hydrochloride in refluxing benzylamine, was debenzylated in good yield using 10 gram-atoms of lithium per mole (10 Li/mol) of 2 in n-propylamine. The debenzylation of N-benzyl-N-methyldecanoic acid amide, 4 (6 Li/mol), in t-butylamine/N, N'-dimethylethylenediamine gave N-methyldecanoic acid amide 6 in 70% yield. Alternatively, reduction of 4 (7 Li/mol) in t-butanol/n-propylamine/ethylenediamine gave n-decanal 12 in 36% yield. Using the same conditions, thioanisole, 1-adamantane-p-toluenesulfonamide, and 1-adamantane methyl p-toluenesulfonate were reduced with 3, 7, and 7.2 Li/mol of compound to give thiophenol (74%), adamantamine (91%), and 1-adamantane methanol (75%), respectively. In this solvent system naphthalene and 3-methyl-2-cyclohexene-1-one were reduced to isotetralin (74%) and 3-methyl cyclohexanone (quantitative) with 5 and 2.2 Li/mol of starting compound, respectively. Oximes and O-methyloximes were reduced to their corresponding amines using 5 and 8 Li/mol of compound, respectively. Anisole was also reduced to 1-methoxy-1,4-cyclohexadiene with 2.5 Li/mol of anisole. Undecanenitrile was reduced to undecylamine with 8.6 Li/mol. Additionally, a base-catalyzed formation of imidazolines from a nitrile and ethylenediamine was also explored.
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The carbonyl group in 3 beta-acetoxy-9 beta, 11 beta-epoxy-5 alpha-lanostan-7-one (1) was found resistant to reductions with conventional mild reducing agents. Reduction with LiAlH4 proceeded with unusual stereochemistry reflecting the steric crowding of the 7-carbonyl group in the folded conformation of the substrate possessing the unnatural 9 beta-configuration.
Radiative properties of Er3+-doped tertiary bismuth glass has been analyzed by the Judd-Ofelt theory. NIR to visible upconversion in the Er3+-doped glass has been reported. The mechanism for the upconversion is explained on the basis of quadratic dependence on excitation power and on the energy-matching scheme. Energy transfer is noted as the dominant process including the long-lived 4I11/2 level as the intermediate state for the green and red upconversion emissions. The effect of temperature on the fluorescence intensity of the two bands due to 2H11/2-->4I15/2 and 4S3/2-->4I15/2 transitions as well as on the transitions due to Stark components of the 4S3/2 level have been monitored and it is concluded that their intensity ratio may serve as better temperature sensing device.
(S)-(+)-O-methylmandelate esters of trans- and cis-1,3, 3-trimethyl-2-oxabicyclo[2.2.2]octan-5- and 6-ols (2- and 3-hydroxy-1,8-cineoles) were prepared, and eight diastereomers were separated. The absolute configuration of the asymmetric carbons of the cineole moiety of each diastereomer was determined by (1)H NMR data according to the Mosher theory. Each mandelate was reduced with LiAlH(4) to obtain optically pure hydroxy-1,8-cineoles, this being followed by acetylation to afford optically pure acetoxy-1, 8-cineoles. These acetates were subjected to chiral GC, using a cyclodextrin column, and the enantiomeric purity of trans- and cis-1, 3,3-trimethyl-2-oxabicyclo[2.2.2]octan-5- and 6-yl acetates in the aroma concentrate from the rhizomes of Alpinia galanga was determined as 93.9 (5S), 19.4 (5R), 63.5 (6R), and 100 (6R) % ee, respectively. The aroma character of each enantiomer was also evaluated by GC-sniffing.
[structure: see text]. A new methodology for the one-pot direct conversion of 2,3-epoxy alcohols into enantiomerically pure 4-hydroxy-4,5-dihydroisoxazole 2-oxides 1 has been found. The reaction works at room temperature and can be run at the 5-10 g scale. The mixture of 4,5-cis and 4,5-trans isomers obtained can be separated as such or as the bis-TDS ethers. A preliminary example of reductive cleavage of 1 to the corresponding amino polyol is also reported.
[reaction: see text] D-Ribonolactone (6) was transformed into N-((fluorenylmethoxy)carbonyl)-3,4-bis-O-(tert-butyldimethylsilyl)-D-2,3-cis-3,4-cis-3,4-dihydroxyproline (13) in nine chemical steps. This represents a potentially general strategy for the synthesis of 3,4-dihydroxyprolines, utilizing the pentose sugar series as starting materials.
Radiation dosimetry deals with the determination of absorbed dose to the medium exposed to ionizing radiation. Chemical dosimetry depends on oxidation or reduction of chemicals by ionizing radiation. A ferrous ammonium sulfate benzoic acid xyelenol orange (FBX) dosimeter based on this principle is being used as a clinical dosimeter at present. Certain modifications were carried out in the preparation and storage of the FBX dosimeter to increase its shelf life. The resulting dosimeter was called a modified FBX (MFBX) dosimeter and has been used in our department for the past few years. An extensive study of the dose, dose rate and energy response of the dosimeter was carried out and compared with a thermoluminescent (LiF7) dosimeter. The results obtained were found to be comparable to the thermoluminescent (LiF7) dosimeter. Hence it was concluded that the MFBX dosimeter could be used for phantom dosimetry, data collection and in vivo measurements. Easier preparation and availability of the reagents are added advantages of using MFBX as a clinical dosimeter in small radiotherapy departments.
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An application of the glow rate technique (GRT) for analysis of the parameters of thermostimulated decay of colour centres is presented using the data on the decay of radiation defects in LiBaF3:Fe crystals created by X rays at 300 K. The GRT offers a procedure for evaluation of the mean activation energy as a function of temperature in the case of arbitrary thermostimulated relaxation kinetics represented by the trap distribution function. The experimental procedure involves at least two subsequent measurements of thermostimulated decay kinetics at different heating rates. It is shown that the decay of the F type centres is governed by interaction of mobile anion vacancies with F(A) and F centres, leading to both the hopping migration and recombination of F centres and the thermoactivated dissociation of the F(A) centres.
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Sodium chimaerol sulfate (1) was isolated from the bile of Lamna ditropis and Rhizoprionodon acutus by chromatography on silica gel and Sephadex LH-20, together with sodium scymnol sulfates, (24R,25S)- and (24R,25R)-(+)-3 alpha,7 alpha,12 alpha,24,26-pentahydroxy-5 beta-cholestan-27-yl sodium sulfates (3 and 4) and 3, respectively. On acid hydrolysis, compound 1 afforded chimaerol (2), which was identified as (24R,25R)-(+)-5 beta-cholestane-3 alpha,7 alpha,12 alpha,24,26-pentol by direct comparison with an authentic sample, prepared by reduction of (24R,25S)-(+)-24,26-epoxy-5 beta-cholestane-3 alpha,7 alpha,12 alpha,27-tetrol (5) with LiAlH4. The structure of 1 was concluded to be (24R,25R)-(+)-3 alpha,7 alpha,12 alpha,24-tetrahydroxy-5 beta-cholestan-26-yl sodium sulfate, based on the chemical transformation and spectral data.