Pyridines, 3- -, nucleophilic

Finally, the substituent effects on the pyridine nucleophile are smaller than those on the substrate and both the calculated and experimental Aand Acorrelate with the corresponding a values. A better nucleophile leads to a later transition state. 

It should be noted that radical cations have a dual reactivity toward a nucleophile, depending on the properties of the latter as a base. It is possible to distinguish between these alternatives by cyclic voltammetry in cases of relatively stable radical cations (Parker and Eberson, 1969a) and by their reactivity toward pyridine nucleophiles of varying steric demands. The principle is illustrated in Fig. 6, which... 

Figure 7. Rate of DPA+ interactions with pyridine nucleophiles A, 0-50 mM, 9,10-DPA + 25 mM 4-methylpyridine , 0-50 mM 9,10-DPA + 25 mM pyridine , 0-50 mM 9,10-DPA + 25 mM 4-acetoxypyridine O, 0-50 mM 9,10-DPA + 25 mM 4-cyanopyridine. All solutions were 0-20 M tetraethylammonium perchlorate in acetonitrile plus the constituents given above. Reprinted by courtesy of the American Chemical Society (Manning et al., 1969).

It is then possible to reduce the nonconjugated double bond chemoselectively and add a pyridine nucleophile to the vinyl sulfone. Notice in this step that a lithium derivative can be prepared from a bromopyridine. In general, heterocycles form lithium derivatives rather easily. The skeleton of epibatidine is now complete and you will find some further reactions from the rest of the synthesis in the problems at the end of this chapter. 

Conversely, nucleophilic attack is increasingly easier than in pyridine. Nucleophiles which react only with quaternized pyridines will sometimes react with the parent diazines. Triazines and tetrazines are even attacked by weak nucleophiles. 

Lee s group has published extensive results on aminolysis of sulfonates. Thus the reactions of anilines with 2-cyano-2-propyl and 1-cyanocyclooctylarenesulfonates in acetonitrile have been studied. A dissociative Sn2 mechanism with a loose TS is supported from the usual LFERs. An 5n2 mechanism is also found for the reaction in acetone of (Z)-benzyl (X)-benzenesulfonates with (Y)-pyridines. Nucleophilic substitutions with the cycloalkyhnethylsulfonates (306) and anilines in MeOH were also studied. Finally the reaction of thiopheneethyl arenesulfonates (307) with anilines and A/, A/ -dimethylanilines in MeCN has been reported on. Frontside-attack in an 5 n2 mechanism with a four-centre TS is supported. 

Five-Membered Unsaturated Heterocycles 1151 Structures of Pyrrole, Furan, and Thiophene 1152 Electrophilic Substitution Reactions of Pyrrole, Furan, and Thiophene 1153 Pyridine, a Six-Membered Heterocycle Electrophilic Substitution of Pyridine Nucleophilic Substitution of Pyridine Fused-Ring Heterocycles 1158 Nucleic Acids and Nucleotides 1160 Structure of Nucleic Acids 1163 Base Pairing in DNA The Watson-Crick Model Nucleic Acids and Heredity 1166 Replication of DNA 1167... 

Scheme 4 Transfer of the phosphoryl group between pyridine nucleophiles - an open concerted mechanism shown also is the charge distribution in the transition structure and that expected for two putative intermediates...

Pyridine, nucleophilic addition to 4-chloro-l,3-din1trobenzenc, 62, 134 Pyridinlum, 3-carbamoyl-l-6-D-r1bofuranosyl hydroxide, 5 5 - ester with adenosine 5 -(trihydrogen pyrophosphate). Inner salt, 63, 17 Pyr1do(2,l,6-de)qu1noll2lne, dodecahydro-, c1s,cis- (3ao,6ao,9aa) [57147-56-6] cis.trans- 3aa,6ac,9ae) [57194-67-9], 61, 108 Pyrrole, 3-acyl, 62, 115 Pyrrole, S-d-hydroxyalkyl), 62, 115... 

Ligands (NFI3, CN, pyridine) Nucleophiles (attacking L. bases) Nucleofuges (leaving L bases) Spectator anions Electron-rich pi systems H+ abstractors... 

Biphasic Brpnsted plots were obtained for the pyridinolysis of aryl dithiocyclopen-tanecarboxylates (38 n = 0, X=S) in MeCN at 333 K, with a change in slope at pXj, = 5.2. This was attributed to a change in the rate-determining step from breakdown to formation of a zwitterionic tetrahedral intermediate with increasing basicity of the pyridine nucleophile. Aminolysis of both aryl dithiocyclohexanecarboxylates (38 ... 

Trogler and co-workers studied the reactions of Fe(CO)3(PR3)2 radicals and found that CO substitution is a second-order process whose rate depends on the steric bulk of the entering group. The rate constants correlate with the pK. of the pyridine nucleophiles. For pyridine reacting with Fe(CO)3(PPh3)2 (25 C in CH2CI2), the parameters are k= 13.6 M" s", Aff = 9.8 kcal mol" and AS = -21 cal moF K these values are typical of the other systems. 

The nucleophilicity of 32 amine, amide, carbamate, amidine, and pyridine nucleophiles was calculated at the B3LYP/6-31G(d,p) level of theory using the gas-phase ionization potential based on the nucleophilicity index The correlation coefficient for the calculated pyridine nucleophilicity against Mayr s values was 0.947, and it was 0.987 against the inverse of the electrophilicity scale Mm. The site selectivity predicted for the nucleophiles with more than one nucleophilic centre correlates well with that predicted by the local nucleophilicity index and the philicity index m. ... 

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