E-Selection

TABLE E Selected Physical Properties of Representative Carboxylic Acids and Dicarboxylic Acids... 

Cochran, L. S, Pielke, R. A., and Kovacs, E., Selected international receptor-based air quality standards. /. Air Waste Manage. Assoc. 42, 1567-1572 (1992). 

Use 0.5 on(y when suction pressure less than 10 psig, and the R used for E, selection must be corrected accordingly. ... 

Since the double-bond configuration is established in the final elimination step from a /t-silicon-(or tin-) substituted carbenium ion in a conformation of lowest energy, often high E selectivity is observed. In reactions of allylstannanes, catalyzed by tin(TV) chloride or titanium(IV) chloride, occasionally a metal exchange occurs, followed by the pericyclic addition pathway leading to the iwti-diastereomers17 19. A more detailed discussion is given in Section D.1.3.3.3.5. 

Several trialkoxy(2-butenyl)zirconium(IV)6,7i 18 and 2-butenylbis(cyclopentadienyl)zirco-nium(IV)18,19 124 complexes have been investigated with respect to the diastereoselectivity on addition to aldehydes. Chlorobis(cyclopentadienyl)-(3-tributylstannyl-2-propenyl)zirconium(IV), prepared by hydrozirconation of tributyl-(l,2-propadienyl)tin, accomplishes the (E)-selective, Wittig-like 1,2-propenylidenation of aldehydes and methyl ketones125. 

If, for the purpose of comparison of substrate reactivities, we use the method of competitive reactions we are faced with the problem of whether the reactivities in a certain series of reactants (i.e. selectivities) should be characterized by the ratio of their rates measured separately [relations (12) and (13)], or whether they should be expressed by the rates measured during simultaneous transformation of two compounds which thus compete in adsorption for the free surface of the catalyst [relations (14) and (15)]. How these two definitions of reactivity may differ from one another will be shown later by the example of competitive hydrogenation of alkylphenols (Section IV.E, p. 42). This may also be demonstrated by the classical example of hydrogenation of aromatic hydrocarbons on Raney nickel (48). In this case, the constants obtained by separate measurements of reaction rates for individual compounds lead to the reactivity order which is different from the order found on the basis of factor S, determined by the method of competitive reactions (Table II). Other examples of the change of reactivity, which may even result in the selective reaction of a strongly adsorbed reactant in competitive reactions (49, 50) have already been discussed (see p. 12). 

Migrastatin (192) (Scheme 37) is a novel macrolide natural product that displays an inhibitory effect on the migration of human tumor cells. After an RCM-based synthesis of the 14-membered macrolide core of 192 [94], Danishefsky also achieved the first total synthesis of the natural compound [95], using the fully functionalized tetraene 191 as the metathesis precursor. Under the conditions shown in Scheme 37, the ring-closing step proceeded (E)-selectively with exclusive participation of the two terminal double bonds in 191, delivering only the ( , ,Z)-trienyl arrangement present in 192. 

Scheme 40 (E)-Selective macrocyclization in the total synthesis of the marine macrolides dactylolide (202) and zampanolide (203) [99]...

Scheme 60 (E)-Selective CM with electron-deficient alkene in Cossy s total synthesis of strictifolione (308) [139b]...

An (E)-selective CM reaction with an acrylate (Scheme 61) was applied by Smith and O Doherty in the enantioselective synthesis of three natural products with cyclooxygenase inhibitory activity (cryptocarya triacetate (312), cryptocaryolone (313), and cryptocaryolone diacetate (314)) [142]. CM reaction of homoallylic alcohol 309 with ethyl acrylate mediated by catalyst C led (E)-selectively to d-hydroxy enoate 310 in near quantitative yield. Subsequent Evans acetal-forming reaction of 310, which required the trans double bond in 310 to prevent lactonization, led to key intermediate 311 that was converted to 312-314. 

Scheme 61 (E)-Selective CM with ethyl acrylate in total syntheses of Cryptocaria natural products 312-314 [142]...

A different task was pursued by the CM of CsA with various maleates 339 [ 148]. The CM demanded in this case the highly active Hoveyda catalyst D, that exhibits potency not reached by the phosphine-containing catalysts C and E. Under the conditions given in Scheme 65, metathesis with maleates 339 led (E)-selectively to the a,/J-unsaturated ester derivatives 340 in high yield. Compounds 340 still demonstrated activity comparable to that of CsA and are thus potential soft drugs via esterase-mediated biotransformation to the corresponding inactive carboxylic acids 341. 

Idem, Part 11 - Potter, P. Holleck, H. Spear, K.E. "Selected Actinide Ternary Systems", in preparation. 

For a review, see Stevens, T.S. Watts, W.E. Selected Molecular Rearrangements Van Nostrand-Reinhold Princeton, 1973, p. 192. 

For books, see Mayo, P. de Rearrangements in Ground and Excited States, 3 vols. Academic Press NY, 1980 Stevens, T.S. Watts, W.E. Selected Molecular Rearrangements Van Nostrand-Reinhold Princeton, 1973. For a review of many of these rearrangements, see Collins, C.J. Eastham, J.F. in Patai The Chemistry of the Carbonyl Group, vol. 1 Wiley NY, 1966, p. 761. See also the series Mechanisms of Molecular Migrations. 

Stuq>e Selective Reactions of Methanol/Isobutanol Mixtures... 

Jonsson, G., and Nwanze, E. Selective (-l-)-amphetamine neurotoxicity on striatal dopamine nerve terminals in the mouse. Br J Pharmacol 77 335-345, 1982. 

Molliver, D.C.. and Molliver, M.E. Selective neurotoxic effects of ( )fenfluramine upon 5-HT axons in rat brain Immunocytochemical evidence, Abstr Soc Neurosci 14 210, 1988. 

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