Remote Group Participation

Scheme 18. Epimerization by neighboring and remote group participation.

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. 

The presence of hydroxyl groups, both adjacent and remote from the epoxide group, have been found to control the regio- and stereo-specificity of the tetracyanoethylene-catalysed methanolysis of cyclohexane epoxides.44 Because the nucleophilic attack occurs at the carbon remote from the hydroxyl group with inversion of configuration, it was suggested the hydroxyl group participates in the reaction. 

The initial suggestion that a remote double bond could be involved in a displacement reaction was made by Shoppee in 1946 in order to account for the stereochemical results of the transformations of 3-cholesteryl derivatives Building on the considerable work then underway on neighbouring group participation in ionization reactions Shoppee suggested that the double bond in the cholesteryl system, 1, could function in a similar manner to Lewis base containing groups such as acetate or alkoxy, etc. 

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. 

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... 

The review aims at providing a general overview of stereocontrolling properties of remote potentially participating groups. However, in spite of plenty of pubhshed... 

The cooperative effect of participating substituents at 0-4 and 0-3 in fucosyl donors was also shown forp-N02Bz groups [45-48]. Historically, these works were the first where donors with remote potentially participating groups were used. 

Scheme 21. A possible remote acetyl group participation in a glycosylation reaction.

This style of collaboration is common when each participant is one role of many played by some other object and the collaboration is part of a framework. These generic pieces of design are rarely about one object. Instead, they are about the relationships and interactions between members of groups of objects. Most of the design patterns discussed in books and bulletin boards are based on such collaborations for example, the observer pattern, which keeps many views up-to-date with one subject or proxy, which provides a local representative of a remote object or any of the more specialized design ideas that are fitted together to make any system. 

It was found that Cope rearrangement of the structurally rigid tetracyclic molecule 506 is remarkably accelerated by creating a remote (i.e. non-conjugated) carbenium ion center by an ionization of a ketal group (equation 191)249. The possibility of both classical and non-classical ion participation in this Cope rearrangement was revealed by using MNDO calculations. 

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