Palladium Tandem Catalysis in the Atropodiastereoselective Synthesis of Indenes Bearing Central and Axial Chirality

The conversion of propargylic carbonates
into allenes via Pd-catalyzed
coupling with arylboronic acids, followed by tandem intramolecular
Alder-ene cyclization, proceeds with remote diastereocontrol in the
formation of indenes possessing two stereogenic elements (stereocenter
and chiral axis). Highly configurationally stable atropisomers have
been obtained with dr values up to >98:2. The reaction tolerates
a
range of commercially available functionalized arylboronic acids and
allows the creation of C­(sp2)–C­(sp2)
and C­(sp2)–C­(sp3) bonds in a single operation.
Control experiments suggest that synergetic thermal and Pd-catalyzed
cyclizations are likely to be involved in the second elementary step.