Preparation of optically pure cross-conjugated cyclopentadienones

The synthesis of optically pure cross-conjugated cyclopentadienones is readily achieved in two steps via a one-pot alkylcuprate addition/aldol condensation/dehydration sequence using racemic or enantioenriched endo-3a,4,7,7a-tetrahydro-1H-4,7-methano-inden-1-ones followed by microwave-mediated Lewis acid-catalysed retro Diels–Alder reaction. An alternative route involving a modified Baylis–Hillman protocol followed by conjugate addition with alkylcuprates and a retro Diels–Alder reaction was also investigated.