Chiral Tricarbonyl(η6-cyclobutabenzene)chromium Complexes. Diastereoselective Synthesis and Use in Asymmetric Cycloaddition Reactions

The intermolecular Diels-Alder reaction of a nonracemic planar chiral (ortho-quinodimethane)Cr(CO)3 intermediate 6 with dienophiles gave, after decomplexation, chiral nonracemic tetralins 23–25. Access to 6 was obtained via enzyme catalyzed acetate hydrolysis of 1-acetoxycyclobutabenzene (13), derivatization of the highly enantioenriched 1-hydroxycyclobutabenzene (S-(+)-8) as the tetrahydropyranyl ether 20 diastereoselective complexation to Cr(CO)3 followed by hydrolysis and charge accelerated electrocyclic ring opening of the anion of (1-hydroxycyclobutabenzene)Cr(CO)3 ((1S,6aR)-(-)-4)