Bridged azacycles

Further examples of the formation of bridged azacyclic systems from the reaction of (65) with aryl Ketones are illustrated by the conversion of indanone (66) into (67) with ammonium acetate in ethanol. 67... 

The condensation of /3-aminoacrolein with (61a,c) leads to the corresponding polymethylene-bridged tpys (66b,d) in low yields. The same systems may be prepared more effectively by the condensation of enamines (65a-c) with formaldehyde and subsequent azacyclization of the intermediate 1,5-diketone (Scheme 12).64 A Hantzsch approach to (66b) has also been reported.67 Benzaldehyde, 4-substituted benzaldehydes, and various other aryl aldehydes can be treated with (65a) to afford 4 -aryl derivatives of (66b) in moderate yields.69 A 48% yield of the monomethylene-bridged (66a) has been... 

If the iminium ion and electron donor are tethered, these SET-induced addition reactions can be efficient to the point of synthetic practicality. For example, such photocyclizations have been used to secure reasonable yields of azacycles of monocyclic, bridged and linearly fused topographies (Scheme 47). Note that the cyclizations of iminium ions (127) and (128) occur in an endocyclic mode with respect to both reacting partners. This mode of cyclization has not been observed in related ground state reactions vide supra). 

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