Synthesis of 5-Alkyl- and 5-Aryl-L-Tryptophan Analogues via Palladium-Catalyzed Cross-Coupling of an Iodinated Cyclic Tryptophan Tautomer
作者:David E. Zembower、Matthew M. Ames
DOI:10.1055/s-1994-25708
日期:——
Cyclic tryptophan tautomers have been shown to be useful intermediates in the preparation of optically pure tryptophans substituted in the benzenoid ring. We have utilized cyclic tautomer 2a for the preparation of L-tryptophan derivatives bearing 5-alkyl and 5-aryl functionalities. Treatment of 2a with 4 equivalents of iodine monochloride provided the 5-iodo species 3a in 81% yield. Cross-coupling of 3a with arylboronic acids or B-alkyl-9-borabicyclo[3.3.1]nonane derivatives, catalyzed by 3 mol% [bis(1,1′-diphenylphosphino)ferrocene]palladium(II) chloride, afforded the 5-aryl and 5-alkyl cyclic tryptophan tautomers 3b-g in 59-79% yields. The cyclic tautomers were easily decyclized and deprotected to give the corresponding 5-aryl- and 5-alkyl-L-tryptophans.
环状色氨酸互变异构体已被证明是制备苯环取代的光学纯色氨酸的有用中间体。我们利用环状互变异构体2a来制备带有5-烷基和5-芳基官能团的L-色氨酸衍生物。用4当量的一氯化碘处理2a,得到5-碘物质3a,产率81%。 3a与芳基硼酸或B-烷基-9-硼双环[3.3.1]壬烷衍生物在3 mol%[双(1,1'-二苯基膦基)二茂铁]氯化钯(II)催化下交叉偶联,得到5 -芳基和5-烷基环状色氨酸互变异构体3b-g,产率为59-79%。环状互变异构体很容易脱环和脱保护,得到相应的5-芳基-和5-烷基-L-色氨酸。