Premium
Synthesis Using Suzuki Cross Couplings of Sulfur Analogues of Dehydrotryptophan with a Definite Stereochemistry
Author(s) -
Silva Natália O.,
Abreu Ana S.,
Ferreira Paula M. T.,
Monteiro Luís S.,
Queiroz MariaJoão R. P.
Publication year - 2002
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200208)2002:15<2524::aid-ejoc2524>3.0.co;2-w
Subject(s) - chemistry , trifluoroacetic acid , stereoselectivity , sulfur , stereochemistry , suzuki reaction , boronic acid , medicinal chemistry , organic chemistry , palladium , catalysis
Sulfur analogues of dehydrotryptophan ( 5−7 ) were prepared in moderate to good yields (40−80%) by Suzuki cross coupling [Pd(PPh 3 ) 4 , Na 2 CO 3 or NaHCO 3 , DME/H 2 O, 90 °C] of several benzo[ b ]thiophene boronic acids with the methyl esters of N ‐ tert ‐butyloxycarbonyl‐β‐bromodehydroalanine [Boc‐ΔAla(β‐Br)‐OMe] or N ‐ tert ‐butyloxycarbonyl‐β‐bromodehydroaminobutyric acid [Boc‐ΔAbu(β‐Br)‐OMe]. The β‐bromodehydroamino acid precursors 2 were, in turn, synthesized in high yields from the corresponding N,N ‐diacyldehydroamino acids 1 by treatment with trifluoroacetic acid (TFA) and N ‐bromosuccinimide (NBS) in two steps or in a one‐pot procedure. Both procedures were stereoselective for the E ‐isomer of Boc‐ΔAla(β‐Br)‐OMe. However, for Boc‐ΔAbu(β‐Br)‐OMe, different ratios of E / Z isomers were obtained in each procedure. The stereoselectivity for the Z ‐isomer was increased greatly with the one‐pot procedure. Pure isomers were used in the coupling reactions and the stereochemistry of the starting material was generally maintained. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)