Abstract
| - Bicyclization of peptide acetals via nucleophilic attack of a phenyl group on an endocyclicacyliminium ion 4 was explored as a route to novel amino acid derived heterocycles andpeptidomimetic scaffolds. In the presence of protic acid, bridged structures such as 6 are formedreadily from phenylalanine derivatives, but the fused-ring analogues 5 could not be obtained ingood yield. In contrast, radical cyclization of the bromophenyl dihydropyrazinone 7 provides aneffective alternative for the synthesis of 5 (n = 0, 1, 2). Additional versatility in this process wasdemonstrated by efficient synthesis of a different fused ring system, represented by the antihelminticpraziquantel, 8.
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