Satendra S Chauhan, Suisheng Shang, M. Pennington
Nov 15, 2017
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Journal
Tetrahedron Letters
Abstract
Abstract Stereoselective alkylation of the anion derived from ( 2R )-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine with 2-chloromethylbenzothiophene afforded the corresponding trans -monosubstituted product, ( 2S , 5R )-2-((1-benzo[ b ]thiophen-2-yl)methyl)-3,6-dimethoxy-5-(propan-2-yl)-2,5-dihyropyrazine in 88% yield. Hydrolysis of the alkylated product using 40% TFA/H 2 O at 0 °C and subsequent protection of the α-amino functional group with Fmoc-OSu afforded Fmoc- l -3-(2-benzothienyl)alanine methyl ester in 88% yield. Hydrolysis of the methyl ester with aqueous LiOH gave Fmoc- l -3-(2-benzothienyl)alanine in 62% overall yield.