Nitrogen Participation

The differences in the mode of participation of nitrogen-containing, complex neighboring groups under neutral and basic conditions has been reviewed by Winstein and coworkers S a number of examples in the carbohydrate field supplement these observations. 

The frans-diequatorial /3-D-glucoside derivative (137), on treatment with basic reagents, generally gives the oxazoline (183) as the sole product, but treatment with potassium cyanide in A, iV-dimethylformamide at 100° affords 17% of the epimino-D-alloside (191). In contrast, the 

Solvolysis of methyl 3-acetamido-2,3-dideoxy-4,6-di-0-(methyl-sulfonyl)-/3-D-ara6mo-hexopyranoside (194) with sodium acetate in refluxing 95% ethanol gave a crystalline product that was either the 

When the pyrimidine nucleoside derivative (197) was treated with potassium cyanide in iV,W-dimethylformamide, there was evidence that the totally deblocked products contained the 3-amino-3-deoxy-D-galactose nucleoside (202), as well as the 4-amino-4-deoxy-D-gulose nucleoside (199). It was suggested that the aziridine (198), formed by nitrogen participation, was a precursor of (199), and that either the oxazoline (200), formed by oxygen participation, or the anhydronucleoside (201) intervened in the formation of (202). 

Aziridine formation by participation of nitrogen from a variety of other complex neighboring groups has been reported. Usually, this formation of a three-membered ring occurs under conditions (a) sufficiently basic to 

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Various other heteroatom-substituted earbocations were also found to be activated by superacids. a-Nitro and a-cyanocarbenium ions, R2C N02 or R2C CN, for example, undergo O- or N-protonation, respectively, to dicationic species, decreasing neighboring nitrogen participation, which greatly enhances the electrophilicity of their carbo-... 

Suggest a synthesis of tosylate (43), needed to study nitrogen participation in substitution reactions. 

Entry 4 involves nitrogen participation and formation of an iminium ion that is reduced by NaBH4. The reaction in Entry 5 creates an 11-methylenebicyclo[4.3.1]undecen-3-one structure found in a biologically active natural product. Note that this fragmentation creates a bridgehead double bond. Entry 6 involves construction of a portion of the taxol structure. The reaction in Entry 7 is stereospecific, leading to the E-double bond. 

Only the unprotonated amine with the free electron pair on nitrogen participated in the reaction (6). The dependence of the height of the more positive wave on the logarithm of the amine concentration is shown in Fig. lb the slope corresponds to a reaction of one carbonyl molecule with one amine. From the ratio of the wave-heights of the first and second waves, it is possible to calculate values of the overall equilibrium constant Ks = K 2K3HOH-], provided that the effect of protonation of the amine and of the Schiff base expressed by equations (4 a) and (4 b) is taken into account. 

Phosphorylation of the potassium salt of 2,2,6,6-tetramethylpiperi-3,4-dione (9) by chloro-phosphates (10) and (11) leads to the cyclic phosphate derivative (12) (Scheme 2) <85JOC209l>. This unusual product is formed due to intramolecular nitrogen participation and was characterized by 13C and 3IP NMR. There are no resonances in the 13C NMR spectra which would indicate the presence of an SPr group in the product and the 3IP NMR has a resonance at an unusual upfield shift indicating a cyclic phosphate. Structure (12) is consistent with these findings and with the extensive phosphorus-carbon and phosphorus-hydrogen coupling seen in its NMR spectra. 

Perimidine is one of the few azines in which the lone pair of a pyrrole-like nitrogen participates in the 7t-system of the molecule. Perimidine is therefore a 14-7t electron system, isoelectronic with the phenalenyl anion. An important consequence of this interaction is a transfer of electron density from the heterocyclic ring into the naphthalene moiety. Therefore perimidine exhibits simultaneously the characteristics of both 7r-deficient and 7t-excessive systems <87H(26)I029>. 

Reaction of 205 with benzotriazole enamine (262), generated through conjugate addition to the corresponding alkyne, led to pyridone 263 (eq. 54).77 Formation of 263 was accompanied by a minor amount of a side product (264, 8%) in which the aromatic species on the nitrogen participated in the cyclization. 

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