Intramolecular electrophilic cyclization reactions were performed with l-(3-oxo-3-phenylpropyl)-1,2,5,6-tetrahydropyridine derivatives l a -p in strong acids to give 4,6-diphenylsubstituted 1-azabicyclo[3.3. llnonadienes 2a-p. Some qualitative observations were made on substituents and reaction conditions influencing the ring closure reaction. Naphthylsubstituted starting compounds 3a, b were converted into pentacyclic compounds 4a, b which represent a new ring system, suggesting the occurrence of a carbenium ion intermediate in the ring closure reaction. Some of the compounds 2a-p show remarkable antifungal and antibacterial effects.The 1-azabicyclo[3.3. llnonane ring system, also called isogranatanine skeleton, was synthesized earlier by Dieckmann condensation ['] and an intramolecular alkylation as well [*]. Later, derivatives of this ring system were prepared also by an intramolecular electrophilic cyclization of l-allyl-1,2,5,6-tetrahydropyridine compounds in acidic medium. In this reaction the acid obviously protonates the trialkyl-substituted double bond in the N-substituent and the resulting carbenium ion serves as the electrophile in the ring closure reacti~n[~.~]. While the above-mentioned methods offer a limited possibility of introducing different substituents into the azabicyclic system we were interested in finding methods which would allow the introduction of a wider variety of different functionalities. Therefore, we investigated other types of intramolecular electrophilic cyclization reactions with differently substituted 1,2,5,6-tetrahydropyridine derivatives. From a biological point of view we aimed at synthesizing new types of 1 -azabicycloalkanes and related derivatives. Among the former there are well known examples of muscarinic agonists which might have a beneficial effect on certain deseases associated with memory irnpairmentr5].As part of this synthetic program successful intramolecular cyclization reactions of 1,2,5,6-tetrahydropyridines containing an acetal moiety in the side chain resulted in new types of 1 -azabicycloalkene derivatives bearing hydroxy and aryl groupd6]. Using in situ generated iminium ions, we could also obtain 1,4-diazabicyclo[4.3. lldecene derivative~ [~]. In the present paper we describe the synthesis of the l-azabicyclo[3.3.l]nona-3,6-diene ring system bearing two aryl substituents.Under the conditions of the Prins reaction[*] treatment of 1 -(3-0~0-3-phenylpropy1)-4-phenyl-1,2,5,6-tetrahydropyridines 1 with sulfuric acid afforded 4,6-diphenyl-l-azabicyclo[3.3.1]nona-3,6-diene derivatives 2 in moderate yields
