A Homochiral Metal–Organic Framework as an Effective Asymmetric Catalyst for Cyanohydrin Synthesis

A homochiral
metal–organic framework (MOF) of an enantiopure
2,2′-dihydroxy-1,1′-biphenyl ligand was constructed.
After exchanging one proton of the dihydroxyl group for Li­(I) ions,
the framework is shown to be a highly efficient and recyclable heterogeneous
catalyst for asymmetric cyanation of aldehydes with up to >99%
ee.
Compared with the homogeneous counterpart, the MOF catalyst exhibits
significantly enhanced catalytic activity and enantioselectivity,
especially at a low catalyst/substrate ratio, due to that the rigid
framework could stabilize the catalytically active monolithium salt
of biphenol against its free transformation to catalytically inactive
and/or less active assemblies in reactions. The synthetic utility
of the cyanation was demonstrated in the synthesis of (S)-bufuralol (a nonselective β-adrenoceptor blocking agent)
with 98% ee.