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41.
The enantioselective cyclization of the prochiral cyclic substrates1 to7 and26, can be carried out in theneat using S-proline as catalyst. The substrates18 to22 and27 could not be cyclized with S-proline but could be cyclized with a mixture of S-phenylalanine and d-camphorsulphonic acid.
The enantioselective cyclization of prochiral acyclic triones45 and47 and also the racemic tricarbonyl compounds54 to57 could also be carried out in theneat using S-proline as catalyst. The optically active enediones obtained in the above cyclizations could also be obtained directly
from 1,3-diones or 2-hydroxymethylene cycloalkanones in a one-pot reaction with methyl vinyl ketone (MVK) and S-proline in
the absence of solvents.13C NMR studies of the one-pot synthesis ofS-11 andS-14 reveal that the annulations involve initial formation of an acid-base complex followed by a Michael reaction and then an
enantioselective cyclization. Such enantioselective cyclizations probably occur on the surface of S-proline crystals. 相似文献
42.
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44.
A note on unsteady unidirectional flows of a non-Newtonian fluid 总被引:8,自引:0,他引:8
Exact solutions are established for a class of unsteady unidirectional flows of an in compressible second grade fluid wherein inertial effects are not ignored. Amongst the several interesting flows which belong to this class are the flow due to a rigid plate oscillating in its own direction, the flow between two rigid boundaries one of which is suddenly started and the time-periodic Poiseuille flow due to an oscillating pressure gradient. 相似文献
45.
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48.
The second law of thermodynamics in nonextensive statistical mechanics is discussed in the quantum regime. Making use of the convexity property of the generalized relative entropy associated with the Tsallis entropy indexed by q, Clausius' inequality is shown to hold in the range q in (0, 2]. This restriction on the range of the entropic index, q, is purely quantum mechanical and there exists no upper bound of q for validity of the second law in classical theory. 相似文献
49.
Jackson YA Rajagopal D Bendolph J Guillory M Lakshmikantham MV Yang J Cava MP 《Organic letters》2003,5(11):1883-1885
[reaction: see text] The preparation of 1,3,5,7-tetramethyl-4,8-dihydrobenzo[1,2-c:4,5-c']dithiophene-4,8-dione and its conversion to the corresponding mono- and dithione are described. 相似文献
50.
We present the dispersion relations for quasiparticle excitations about the color-flavor locked ground state of QCD at high baryon density. In the presence of condensates which pair light and strange quarks there need not be an energy gap in the quasiparticle spectrum. This raises the possibility of gapless color superconductivity, with a Meissner effect but no minimum excitation energy. Analysis within a toy model suggests that gapless color superconductivity may occur only as a metastable phase. 相似文献