A practical and environmentally benign Brønsted acid−catalyzed protocol for the preparation of all-carbon tetrasubstituted allenes, consisting in the direct SNˈ addition of tri- or dimethoxy arenes or allyltrimethylsilane to tertiary propargylic alcohols, has been developed. In addition, a straightforward synthesis of densely substituted 2H-chromenes by metal-free tandem allenylation/heterocyclization reaction of methoxyphenols and tertiary alkynols is presented.
