“Photostimulated Intramolecular SRN1 Reactions with Nitrogen Nucleophiles: Síntesis Of Fused Azaheterocycles”

VICTORIA A. VAILLARD, MARÍA E. BUDÉN, SANDRA E. MARTÍN AND ROBERTO A. ROSSI

Santiago de Compostela, España

Congreso; 19th IUPAC Conference; 2008

The radical nucleophilic substitution, or SRN1 reaction, is a chain process through which an aromatic nucleophilic substitution is achieved. The initiation step is an electron transfer (ET) from suitable donors to the substrate to afford a radical anion. In some systems, the ET step is spontaneous; however, in others light can initiate the reaction.1 Several nucleophiles such as carbanions and heteroatom anions can be used for SRN1 reactions to form new C–C or C-heteroatom bonds in good yields. An exception to this is the intermolecular reaction of aromatic amide ions with aromatic substrates. In this case, the formation of both, C–N and C–C bonds was observed. For instance, 2-naphthylamide ions reacted under irradiation with ArI, and 1-aryl 2-naphthylamines were formed regioselectively in 45–63% yields, with 3–6% of N-arylation.2 When a substrate has both, the leaving group and the nucleophilic center, the intramolecular reaction affords a cyclic product.1 Here we will report the intramolecular arylation of aromatic amide ions such as 1 with a pendant aryl moiety with a suitable leaving group, to obtain fused azaheterocycles 2 or 3. Product 2 affords 4 by spontaneous oxidation.3 To extend the applications of this methodology, we have studied nucleophiles derived from pyrrole or similar heterocycles. When the nitrogen has acidic N-H bond, the anions 5 are formed. If these substrates contain an aryl moiety with a suitable leaving group bonded with different bridges Z, the fused azaheterocycles 6 are formed in good yields by the SRN1 mechanism. We will discuss the scope and limitation of these novel ring closure reactions to synthesize fused azaheterocycles.