Short Course in Heterocyclic Chemistry Lecture 8 ... - Ark.chem.ufl.edu

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Scheme 35. Reactions of Isoxazolinopyridinium Cation with Secondary Amines Acyl derivatives of 1-hydroxybenzotriazole have been widely used in peptide synthesis: the 1-hydroxybenzotriazole anion is a good leaving group there has been considerable uncertainty regarding the structure of these compounds: we have recently shown [91JCS(P2)1545] that O-acyl derivatives are initially formed and rearrange, (in a processes shown to be intermolecular by a crossover experiment), into the N-acyl compounds (Scheme 36.) Scheme 36. Cross-Over Experiment for Rearrangement of l-Acyloxybenzotriazoles 32
7. Regio Specific Nucleophilic Substitution at the 4-Position of Pyridine The differentiation between nucleophilic attack at the 2- and 4-positions in a pyridine ring is normally difficult and such reactions frequently lead to mixtures of products, or to exclusively 2-position substitution. One set of conditions for getting regioselective substitution at the 4-position is shown in Scheme 37. Scheme 37. Nucleophilic Substitution at 4-Position in Pyridine A substituent that satisfies the conditions of Scheme 32 is the 2,6-dimethyl-4-pyridun-1yl group. It can he attached to the nitrogen atom of a pyridine in two simple stages, as shown in Scheme 38. 33
Page 1 and 2: Short Course in Heterocyclic Chemis
Page 3 and 4: 1. Introducation Two chemical texts
Page 5 and 6: Many ring closure methods are also
Page 7 and 8: 3. Basicity of N-Oxides and N-Imide
Page 9 and 10: Scheme 8. Definition of Mesomeric M
Page 11 and 12: Scheme 11 lists the increments meas
Page 13 and 14: Electron acceptance can seen in the
Page 15 and 16: 5. Reactions of N-Oxides and N-Imid
Page 17 and 18: Some of the ways in which the react
Page 19 and 20: For N-imides, electrophiles attack
Page 21 and 22: Scheme 23 gives details of two exam
Page 23 and 24: Scheme 25. Formation of Monocationi
Page 25 and 26: Although it has not been possible t
Page 27 and 28: 6. Nucleophilic Attack on N-Oxides
Page 29 and 30: Nucleophilic displacement of leavin
Page 31: Scheme 33. Action of Hydroxide Ion
Page 35 and 36: Synthetically useful transformation
Page 37 and 38: Scheme 43 shows similar work with t
Page 39 and 40: 9. References 24JPR209 K. Elbs, J.
Page 41: Sammes, C.W.F. Leung, and C.M. Lee,

Short Course in Heterocyclic Chemistry Lecture 8 ... - Ark.chem.ufl.edu

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