Synthesis 2006(14): 2376-2384  
DOI: 10.1055/s-2006-942435
PAPER
© Georg Thieme Verlag Stuttgart · New York

Enaminone-Based Synthesis of (S)-3-(Pyrazolyl)alanines from l-Aspartic Acid

Uroš Uršič, David Bevk, Samo Pirc, Lidija Pezdirc, Branko Stanovnik*, Jurij Svete*
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, 1000 Ljubljana, Slovenia
Fax: +386(1)2419220; e-Mail: branko.stanovnik@fkkt.uni-lj.si; e-Mail: jurij.svete@fkkt.uni-lj.si;
Further Information

Publication History

Received 7 December 2005
Publication Date:
26 June 2006 (online)

Abstract

Protected N(1′)-substituted (S)-3-(4-methoxycarbonyl-1H-pyrazol-5-yl)alanines 7a-h were prepared in 34-94% yields by acid-catalysed cyclocondensations of chiral enaminone 5, available from l-aspartic acid, with hydrazines 6a-h hydrochlorides. Deprotection of 7a,b,e by catalytic hydrogenation afforded the corresponding free pyrazoylalanines 8a,b,e. On the other hand, 1-benzyl 6-methyl (S)-2-benzyloxycarbonylamino-4-oxohexanedioate (4), precursor of the enaminone 5, reacted with hydrazines 6 in two different ways. In the reactions of 4 with (hetero)arylhydrazines 6b,e,i, the five-membered ring was formed and the corresponding 3-pyrazolylalanine esters 10b,i and 10′e were obtained, whilst treatment of 4 with hydrazine hydrate (6a) and methylhydrazine (6h) led to the formation of the six-membered ring furnishing tetrahydropyridazinones 11a,h.