Pd-catalyzed, Cu(I)-mediated cross-couplings of bisarylthiocyclobutenediones with boronic acids and organostannanes.

Bisarylthiocyclobutenedione 7 reacted smoothly with a variety of both organostannanes and (hetero)arylboronic acids in the presence of a catalytic amount of Pd and a stoichiometric amount of CuTC to produce symmetrical disubstituted cyclobutenediones in yields that range from 37 to 94% (18 examples).

Squaric acid ester-based total synthesis of echinochrome A.

The total synthesis of echinochrome A is described. Both key intermediates 5 and 8 were efficiently prepared from diisopropyl squarate 7. Nucleophilic addition of aryllithium 8 to 5, followed by thermal ring-expansion/cyclization of the 1,2-adduct 4, furnished hydroquinone 3. Oxidation and full deprotection of 3 gave the title compound.