Generation of Chiral N‐Acylpyridinium Ions by Means of Silyl Triflates and Their Diastereoselective Trapping Reactions: Formation of N‐Acyldihydropyridines and N‐Acyldihydropyridones.

Abstract

An efficient method to prepare N-acylpyridinium ions like (III) is reported. Treatment of the latter with organometallic reagents leads to α-substituted N-acyldihydropyridines and N-acyldihydropyridones. The degree of stereoselectivity depends on the pyridine and organometallic reagent used. The auxiliary can smoothly be removed under basic conditions. -(HOESL, C. E.; MAURUS, M.; PABEL, J.; POLBORN, K.; WANNER*, K. T.; Tetrahedron 58 (2002) 33, 6757-6770; Inst. Pharm.,

Enantioselective Catalytic Dearomative Addition of Grignard Reagents to 4-Methoxypyridinium Ions

“… 4 At the same time, elegant strategies that depend on the direct use of pyridinium salts as substrates in addition reactions have been reported as well. 5 , 6 Among literature precedence, the strategy that makes use of Grignard reagents and relies on chiral pyridinium salts to control the stereochemistry of the addition step has found the broadest application and still remains the preferred option ( Scheme 1 A). 5 On the other hand, catalytic examples that make use of prochiral acylpyridinium ions are especially attractive in terms of atom economy and cost-efficiency.…”

“… 5 , 6 Among literature precedence, the strategy that makes use of Grignard reagents and relies on chiral pyridinium salts to control the stereochemistry of the addition step has found the broadest application and still remains the preferred option ( Scheme 1 A). 5 On the other hand, catalytic examples that make use of prochiral acylpyridinium ions are especially attractive in terms of atom economy and cost-efficiency. As a result, several catalytic methods that utilize prochiral acylpyridinium ions have also been reported, 6 including nickel-catalyzed arylations 6h , 6i and copper-catalyzed alkylations, 6j both using organozinc reagents ( Scheme 1 B).…”