Remote Neighboring Group Participation

A subsequent report by Kwan Soo Kim and coworkers indicated that remote participation from an equatorial C3 position is indeed possible [16]. In this case, a tri-chloroacetimidate was used as a nucleophilic trap. Upon low-temperature activation of thioglycoside 11 using 1-benzenesulfinylpiperidine (BSP) and Tf20, bicyclic 

SCHEME 4.2 Nucleophilic traps to explore neighboring group participation from nonvicinal positions. Bn, benzyl Tf, triflyl. 

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A. V. Demchenko, E. Rousson, and G.-J. Boons, Stereoselective 1,2-cw-galactosylation assisted by remote neighboring group participation and solvent effects, Tetrahedron Lett., 40 (1999) 6523-6526. 

In organic chemistry it is well known that a substituent directly linked to a reaction center has a profound effect on the latter s reactivity. The influence of a remote substituent has also received much attention as more organic molecules are being scrutinized. Thus, neighboring group participations in solvolysis are generally observed. Certainly, the full attribution of a substituent must be the sum of electronic, steric, and stereoelectronic factors. 

Y. Zeng, J. Ning, and F. Z. Kong, Remote control of a- orjS-stereoselectivity in (1— 3)-glucosylations in the presence of C-2 ester capable of neighboring-group participation, Tet. Lett., 43 (2002) 3729-3733. 

Figure 8.5 Relative stabilization of substituted oxocarbenium ions by neighbor-group participation from remote ester groups (energies are given relative to the first structure).

Unlike the neighboring group participation by 0-2 protecting groups, the existence of the remote participation by potentially participating groups at remote positions of glycosyl donors has been controversial. We reviewed reports that were opposed to and in favor of the remote participation. Nevertheless, results and evidence in favor of the remote participation are quite substantial, especially for... 

Scheme 18. Epimerization by neighboring and remote group participation.

More remote secondary isotope effects, such as y-d effects, cannot be generalized, and thus each effect requires a specific explanation. An example of the use of a combination of a-, jS-, and y-d effects in the study of participation by the neighboring aryl group is included below to represent the use of these effects in studies of neighboring groups. The interpretations presented are the reported ones rather than our own. 

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