Surprising fenchone induced cyclization: synthesis of the new chiral diol biphenyl-2,2′-sulfone-3,3′-bisfenchol (BISFOL)

The new chiral diol BISFOL (biphenyl-2,2′-sulfone-3,3′-bisfenchol) is surprisingly formed by cyclization of diphenylsulfone after treatment with n-buthyllithium at −78 °C and subsequent addition of (−)-fenchone. Formation of fenchyl alcohol as byproduct points to a Meisenheimer intermediate as primary cyclization product, which transfers lithium hydride yielding the cyclic sulfone. As a chiral and chelating ligand, BISFOL catalyzes enantioselective diorganozinc additions to aldehydes and forms with dimethylzinc an unprecedented, macrocyclic, dimeric methylzinc complex.