Chiral auxiliaries, ligands and arene chromium complexes

Sequential addition of organolithium compounds and allyl- or propargyl bromide to (phenyloxazoline) Cr(CO)(3) gave 1-oxazolyl-5,6-trans-disubstituted cyclohexadienes. Regioselective radical (SnBu(3)) addition to the alkyne and cyclization of the vinylic radical to the diene moiety afforded fused bicyclic ring systems. Depending on whether the reaction was carried out with a terminal or internal alkyne, the reaction gave either cis-fused tetrahydroindanes or bicyclo[3.2.1]octenes selectively. Asymmetric methodologies for the synthesis of diastereo- or enantioenriched cyclohexadienes via temporary complexation of the arene to the electrophilic Cr(CO)(3) include chiral auxiliaries on the arene (oxazolines, SAMP-hydrazone), chiral ligands at Cr, chiral nucleophiles (organolithium reagents modified by chiral ligands) and planar chiral complexes synthesized via enantioselective lithiation. The article contains new developments and examples of the first and third approach of this asymmetric dearomatization methodology.