title: Catalyzed selective direct α- and γ-alkylation of aldehydes with cyclic benzyl ethers by using T(+)BF4- in the presence of an inexpensive organic acid or anhydride.
abstract: The cross dehydrogenative coupling (CDC) of cyclic benzyl ethers with aliphatic and α,β-unsaturated aldehydes has been developed. The mild reaction conditions, in which an N-oxoammonium salt derived from TEMPO (2,2,6,6-tetramethyl-1-piperidinoxyl) is employed as the oxidant in combination with a Cu catalyst, allow the use of relatively redox-unstable aldehydes under oxidative CDC conditions. The addition of a catalytic amount of trifluoroacetic acid (TFA) or Ac(2)O facilitates the reaction and increases the efficiency and selectivity. In contrast to the expected α-alkylation obtained with aliphatic aldehydes, α,β-unsaturated aldehydes led preferentially to the more challenging γ-alkylated products. The utility of the developed methodology was demonstrated by the synthesis of isochromane-derived bioactive compounds, such as the dopamine antagonist sonepiprazole.
authors.affiliation: Organisch-Chemisches Institut, Universität Münster, Corrensstrasse 40, 48149 Münster, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Richter
authors.forename: Renate
authors.initials: R
authors.lastname: Rohlmann
authors.forename: Olga
authors.initials: O
authors.lastname: García Mancheño