Electronic effects on a one-pot aromatization cascade involving alkynyl-Prins cyclization, Friedel-Crafts alkylation and dehydration to tricyclic benzo[f]isochromenes.

A three-step domino reaction between 1-aryl-3-hexyne-2,6-diol derivatives and aldehydes is used to construct tricyclic 1,4-dihydro-2H-benzo[f]isochromenes. The cascade is initiated by BF·OEt and involves alkynyl-Prins cyclization, Friedel-Crafts alkenylation, and dehydration/aromatization to create a new, central aromatic ring and eliminate 2 equiv. of water.

Atom economical, one-pot, three-reaction cascade to novel tricyclic 2,4-dihydro-1H-benzo[f]isochromenes.

Reaction of 6-methyl-1-phenylhept-3-yne-2,6-diol with various aldehydes under Lewis acid conditions provides an atom economical, two-component cascade reaction sequence to novel 2,4-dihydro-1H-benzo[f]isochromene compounds. Aliphatic aldehydes as well as electron-deficient and -rich aromatic aldehydes can be used.

Bi(OTf)3-, TfOH-, and TMSOTf-mediated, one-pot epoxide rearrangement, addition, and intramolecular silyl-modified Sakurai (ISMS) cascade toward dihydropyrans: comparison of catalysts and role of Bi(OTf)3.

Catalytic quantities of bismuth(III) triflate efficiently initiate the rearrangement of epoxides to aldehydes, which subsequently react with (Z)-δ-hydroxyalkenylsilanes to afford 2,6-disubstituted 3,6-dihydro-2H-pyrans. Isolated yields of desired products using Bi(OTf)(3) were compared with yields obtained when the reactions were run with TfOH and TMSOTf in the presence and absence of several additives. These studies, as well as NMR spectroscopic analyses, indicate an initial Lewis acid/base interaction between Bi(OTf)(3) and substrates providing TfOH in situ.