NONREDUCTIVE DESULFENYLATION OF 3-INDOLYL SULFIDES - IMPROVED SYNTHESES OF 2-SUBSTITUTED INDOLES AND 2-INDOLYL SULFIDES

Desulfenylation of 3-indolyl sulfides to the corresponding 3-unsubstituted indoles is usually carried out under reductive conditions, thus accommodating only substituents which are resistant to reduction. We have developed a nonreductive procedure for removal of a sulfide at the 3-position of indoles, using trifluoroacetic acid in the presence of a thiol as trapping agent, which is compatible with a large array of functionalities on the indole ring. In addition, the desulfenylation occurs selectively at the 3-position of the indole, and sulfide groups at other positions of the molecule remain untouched. Thus, indole 2,3-bis-sulfides are selectively desulfenylated at the 3-position, affording 3-unsubstituted 2-indolyl sulfides. This methodology broadens the use of sulfide as a protecting group for the 3-position of indoles.