Participation s. Neighboring

Participation s. Neighboring group participation Pathway control -, reaction of oximes with nitrosyl chloride 26, 258s31 Pearson degradation 9,294 Penicillin S-oxide ring... 

Paraffin as medium 27, 679 Paraformaldehyde s. Formaldehyde Participation s. Neighboring group participation Patemo-Budii reaction, intramolecular 26, 153 Pmiicillin ring S-oxides, rearrangement 26, 629... 

Participation s. Neighboring group participation Partridge s. Bedford Pathway control... 

The preparation of a number of anhydro thio sugars is based on this S neighboring-group participation. 

Neber rearrangement, anamalous 23,212 31, 376 Neighboring group participation (s. a. Assistance, intramolecular)... 

Now let s look at more heteroatoms with nonbonding electrons that might participate in neighboring group reactions. For example, nitrogen bears a lone pair of electrons, and so can act as an internal nucleophile. Let s look at the reactions of the two bicyclic amines in Figure 21.14. Treatment of the endo chloride with ethyl alcohol leads to the endo ether, but the exo chloride gives neither the exo nor endo ether under the reaction conditions. Now we ll see why. 

Aryl thioethers s. Thioethers, ar. Arylthiomethylation 26,844 Aryl tridiloromethyl carbinols -, reactions with nucleophiles, review 22, 629 suppl. 26 Arynes s. Benzyne..., Hetarynes Ascaiite 11,963 suppl. 28 Asscher-Yofsi reaction 21,642 Assistance, intramolecular s. Neighboring group participation... 

H-Naphtho[l,2-b]pyran-2-ones, 5,6-dihydro- 27, 989 Naphthoxazcdes 26, 395 2H-Naphth[l,8-bc]oxepin-2-ones 22,277 suppl. 26 Napieral s. Bischler Neighboring group participation (s. a. Andiimeric process)... 

Series 7 gives a linear plot with p = —5.27, consistent with the S l mechanism. Series 8, however, shows a discontinuity, which Gassmann and Fentiman interpreted as a change in mechanism. Compounds in series 8 are capable of intramolecular assistance (neighboring group participation) by electron donation from the double bond to stabilize the cation, as in 9. 

There is a special interest in the role of neighboring group participation by sulfinyl groups in nucleophilic aliphatic substitution. Thus Martin and Uebel218 found that trans-4-chlorothiane-S-oxide 36 is solvolyzed (50% v/v aqueous ethanol, 140 °C) 630 times faster than the cis isomer 37. This was attributed to the intervention of 38 for the former. 

Capon, B. and McManus, S. P. (1976). Neighboring Group Participation . Plenum Press, New York... 

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