Computational Study of o-Iodo-Benzilamides Cyclization by an Electron Transfer Mechanism

DORN, V.B.; BUDÉN, M.E.; ROSSI, R.A.; PIERINI, ADRIANA B.

Florianópolis – Brasil

Conferencia; 10th Latin American Conference on Physical Organic Chemistry; 2009

Latin American Conference on Physical Organic Chemistry (CLAFQO)

The SRN1 reaction is an alternative process by which an aromatic nucleophilic substitution is achieved. It involves a chain process with radical and radical anions as intermediates. This reaction is compatible with many substituents and allows obtaining heterocyclic compounds.      In this sense, we have proposed a new approach for the syntheses of phenanthridines starting from a substrate that has both, the leaving group (halogen) and the nucleophilic center (amide ion). The intramolecular SRN1 reaction affords the expected cyclic product in good to excellent yield.       We now report a surprising result found in the irradiated reaction of substrates 1 and 2 with t-BuOK in liquid ammonia. Substrate 1 yielded the expected ring closure product in 98% (C-cyclization). However, substrate 2 affords C-cyclization product in 84% yield and a rearranged product coming from N-cyclization in 8% (see Scheme).      In order to study the system, ab initio calculations were done to inspect the electronic and geometric factors responsible for the regiochemistry of these reactions.