Dual macrolactonization/pyran-hemiketal formation via acylketenes: applications to the synthesis of (-)-callipeltoside A and a lyngbyaloside B model system.

[Image: see text] Thermal generation of acylketenes in diol-containing substrates results in dual macrocyclization/pyran-hemiketal formation. This transformation expands the scope of acylketene macrolactonizations and their application to the synthesis of complex macrolides. Triol and even tetrol substrates also have been closed in highly regioselective fashion. Additionally, the challenging macrolactonization of a tertiary alcohol was achieved.