Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Neighboring group participation. See

For a review of neighboring group participation by sulfinyl oxygen, see Montanari221. This special influence of sulfinyl groups on reactivity is, of course, due to the high polarity... [Pg.530]

Furthermore, a neighboring group participation of a phenylthio function is observed in the Lewis acid-catalyzed nucleophilic substitution reaction of various P-nitrosulfides. Because the P-nitrosulfides are readily available, by the Michael addition of thiols to nitroalkenes (see Michael addition Chapter 4), this reaction is very useful. The P-nitrosulfides are prepared stereoselectively, and the reaction proceeds in a stereo-specific way (retention of configuration) as shown in Eqs. 31-34.35... [Pg.190]

Neighboring group participation effects appear to play a crucial role in the nucleophilic substitution of chlorine in Michael adducts of 1-R, 2-R, 3-X. Thus, this substitution proceeds very easily in any of the adducts formed with an electron rich nitrogen, sulfur and oxygen Michael donor. For the adducts of nitrogen nucleophiles, the facile substitution of the chlorine has been suggested to occur via formation of intermediate aziridinium ions 103 [8] (Scheme 32), and this postulate was later supported by isolation of azaspiropentane derivatives under appropriate conditions in several reactions (see Sect. 3.2.2) [11b, 53,56]. It is most likely that alkylthio substituents in adducts of type 85 participate in the same way to first form spirocyclopropane-annelated thiiranium ion intermediates which are subsequently opened by attack of the incoming nucleophile. [Pg.178]

Neighboring-group participation by the vicinal, trans-acetoxyl group (see p. 125) serves to explain the abnormal behavior of methyl 4-0-acetyl-2,3-anhydro-6-0-benzyl- or -trityl-a-D-gulopyranoside with hydrogen chloride in acetone, or with 80% aqueous acetic acid, which give D-galactose, instead of the D-idose, derivatives.67 In the same way, 2-0-acetyl-3,4-anhydro-D-altropyranosides yield D-man-nosides, not D-idosides.9 6z(see p. 125). [Pg.148]

For a monograph, see Capon McManus Neighboring Group Participation, vol. 1 Plenum New York. 1976. [Pg.308]

The solvolysis of 3-phenyl-2-butyl tosylate is only half as fast as that of 2-butyl tosylate. However, Winstein suggested that the inductive effect of the phenyl group should retard the rate by a factor of ten and that neighboring-group participation therefore has given a fivefold rate enhancement [see note 14(a), p. 273]. See p. 280 for the actual rate enhancement. [Pg.277]

Discrimination can readily be observed between the two possible modes of attack on a carbonium ion (195 196 and 195 197 when the nucleophile is part of the substrate. In such cases, the phenomenon of neighboring group participation is observed (for a review, see ref. 69). For example, solvolysis of the erythro-tosylate isomer 202 in acetic acid gave largely the erythro-acetate isomer 204 vi a the chiral bridged ion 203, whereas the threo isomer 205 yielded a racemic mixture of threo products 207A and 207B via the achiral intermediate 206 (70). [Pg.298]


See other pages where Neighboring group participation. See is mentioned: [Pg.583]    [Pg.257]    [Pg.309]    [Pg.446]    [Pg.277]    [Pg.64]    [Pg.65]    [Pg.257]    [Pg.583]    [Pg.257]    [Pg.309]    [Pg.446]    [Pg.277]    [Pg.64]    [Pg.65]    [Pg.257]    [Pg.530]    [Pg.583]    [Pg.947]    [Pg.148]    [Pg.26]    [Pg.41]    [Pg.235]    [Pg.312]    [Pg.682]    [Pg.292]    [Pg.390]    [Pg.414]    [Pg.846]    [Pg.274]    [Pg.328]    [Pg.703]    [Pg.88]    [Pg.71]    [Pg.206]    [Pg.206]    [Pg.238]    [Pg.386]    [Pg.146]    [Pg.115]    [Pg.846]   


SEARCH



Neighbor

Neighboring group

Neighboring group participation

Neighboring group participation groups

Neighboring participation

Participating group

© 2024 chempedia.info