Reductive Elimination of Phenylsulfonyl Groups in the 3‐Position of Benzo[<i>a</i>]heptalene‐2,4‐diols

Abstract

Abstract 3‐(Phenylsulfonyl)benzo[ a ]heptalene‐2,4‐diols 1 can be desulfonylated with an excess of LiAlH 4 /MeLi⋅LiBr in boiling THF in good yields ( Scheme 6 ). When the reaction is run with LiAlH 4 /MeLi, mainly the 3,3′‐disulfides 6 of the corresponding 2,4‐dihydroxybenzo[ a ]heptalene‐3‐thiols are formed after workup ( Scheme 7 ). However, the best yields of desulfonylated products are obtained when the 2,4‐dimethoxy‐substituted benzo[ a ]heptalenes 2 are reduced with an excess of LiAlH 4 /TiCl 4 at −78→20° in THF ( Scheme 10 ). Attempts to substitute the PhSO 2 group of 2 with freshly prepared MeONa in boiling THF led to a highly selective ether cleavage of the 4‐MeO group, rather than to desulfonylation ( Scheme 13 ).