An interesting dichotomy in the cyclisation of exocyclic enamines with protected dehydroamino acids leading to different β-turn templates

• Published in: Tetrahedron letters Vol. 43; no. 49; pp. 8963 - 8966
• Main Authors: Berry, Jane M., Doyle, Paul M., Young, Douglas W.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 02-12-2002
• ISSN: 0040-4039; 1873-3581
• DOI: 10.1016/S0040-4039(02)02141-X

Two templates for the preparation of external β-turns have been synthesised. In the course of the synthetic studies an interesting dichotomy was observed in the PCl
3 catalysed reaction of exocyclic enamines such as
6
and
14
with protected dehydroamino acids. When amide protected dehydroamino acids were condensed with
6
and
14
the expected 6/6 and 6/5 fused bicyclic compounds such as
7
and
15
respectively were obtained, whereas when urethane protected dehydroamino acids were used, the 5/6 and 5/5 fused products
9
and
18
were obtained.
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