Synthesis of Substituted Chromanes and Tetrahydroquinolines via Tandem 1,2-Silyl Shift–Friedel–Crafts Cyclization

Propargyl silanes bearing an aryl ether or aniline moiety undergo acid-promoted 1,2-silyl shift to generate an allyl cation, which subsequently alkylates the adjacent aryl group in a Friedel-Crafts fashion. The developed methodology furnishes chromanes in 24-99% yields and 1,2,3,4-tetrahydroquinolines in 21-77% yields, depending on the substitution pattern. The distinctive feature of the developed methodology is the synthesis of (trialkylsilyl)vinyl- and (Z)-2-halo-1-(trialkylsilyl)vinyl-substituted heterocycles. Propargyl silanes bearing chloro- and bromoalkyne motifs afford cyclization products in higher yields than their terminally unsubstituted alkyne counterparts, providing access to trisubstituted (Z)-alkenes with high stereoselectivity. The paper also reports an improved protocol for silver-catalyzed haloalkyne synthesis, which is enabled by the use of Ag₂CO₃ or AgOAc catalysts.