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Palladium-Catalyzed Reactions in the Synthesis of 3- and 4-Substituted Indoles. Approaches to Ergot Alkaloids
Harrington, Peter J.,Hegedus, Louis S.
, p. 2658 - 2662 (2007/10/02)
An efficient synthesis of 4-bromo-1-tosylindole (10) based on the Pd(II)-catalyzed cyclization of an o-ethenylaniline p-toluenesulfonamide has been developed.A Pd(0) oxidative addition-olefin insertion-β-hydride elimination cycle converted 10 to a number of 4-substituted 1-tosylindoles.Selective electrophilic substitutions at the 3-position of 10 provided access to the 3-(chloromercurio)- (18) and 3-iodo-1-tosylindoles (22).Transmetalation to palladium and allyl chloride insertion converted 18 to 3-allyl-4-bromo-1-tosylindole (20) which could be cyclized to the benzindoline 21.A Pd(0) oxidative addition-olefin insertion-β-hydride elimination cycle converted the 3-iodo compound 22 to a number of 4-bromo-3-substituted 1-tosylindoles including 24, a potential precursor to optically active tryptophans.
