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Synthesis of β‐Benzo[ b ]thienyldehydrophenylalanine Derivatives by One‐Pot Palladium‐Catalyzed Borylation and Suzuki Coupling (BSC) and Metal‐Assisted Intramolecular Cyclization – Studies of Fluorescence and Antimicrobial Activity

2005; Wiley; Volume: 2005; Issue: 14 Linguagem: Inglês

10.1002/ejoc.200500040

1434-193X

Ana S. Abreu, Paula M. T. Ferreira, Maria João R.P. Queiroz, Isabel C.F.R. Ferreira, Ricardo C. Calhelha, Letı́cia M. Estevinho,

Catalytic C–H Functionalization Methods

Abstract Palladium‐catalyzed borylation and Suzuki coupling (BSC) in a one‐pot procedure was successfully applied to the synthesis of several β‐substituted dehydrophenylalanines in the benzo[ b ]thiophene series, with the stereochemistry of the starting materials being maintained. Bromobenzo[ b ]thiophenes bearing an ortho EDG (OMe or Me) were used as the components to be borylated with pinacolborane, whilst pure stereoisomers of β‐bromodehydrophenylalanines were used as the other Suzuki coupling components. Treatment of the obtained methyl ester of ( Z )‐ N ‐( tert ‐butoxycarbonyl)‐β‐(2,3,5‐trimethylbenzo[ b ]thien‐6‐yl)dehydrophenylalaninewith Pd(OAc) 2 and Cu(OAc) 2 in DMF at 160 °C gave two indole derivatives (1:3), the major product resulting from isomerization and cyclization and the minor product resulting from direct cyclization (thienoindole). Carrying out the reaction at 100 °C gave the same products in similar amounts. Use of the methyl ester of ( Z )‐ N ‐( tert ‐butoxycarbonyl)‐β‐(2,3,7‐trimethylbenzo[ b ]thien‐6‐yl)dehydrophenylalanine as starting material gave only one product, resulting from isomerization and cyclization at 100 °C. Two of the cyclized compounds were subjected to fluorescence studies; the thienoindole could be useful as a fluorescent probe. Preliminary studies of antimicrobial activity were performed on the precursors and on the cyclized products.