Novel multichiral diols and diamines by highly stereoselective pinacol coupling of planar chiral [2.2]paracyclophane derivatives

Abstract

The TiCl4/Zn-mediated intermolecular pinacol coupling of the planar chiral carbonyl compounds [2.2]paracyclophane-4-carbaldehyde, 4-acetyl[2.2]paracyclophane (ketone) and the four regioisomeric 5-, 7-, 12- and 13-methoxy[2.2]paracyclophane-4-carbaldehydes as well as the pTosOH-Zn/Cu-promoted coupling of their N-substituted imines is described. Coupling of the enantiomerically pure substrates (most of carbonyl compounds and all imines) occurs stereoselectively giving rise to diastereomerically pure 1,2-diols and 1,2-diamines. Racemic aldehydes and ketone react with different degrees of stereoselectivity (depending on the substituents in certain positions) and produce one to three diastereomers. 7-methoxy[2.2]paracyclophane-4-carbaldehyde undergoes a tandem pinacol coupling-pinacol rearrangement to yield bis-(7-methoxy[2.2]paracyclophane-4-yl)acetaldehyde. Coupling of the racemic imines produces a mixture of single racemic D,L-diamine and single meso-diamine in each case. The stereoselective formation of the asymmetric centres is governed by the planar chiral [2.2]paracyclophanyl moiety. The techniques elaborated are extended to the intramolecular coupling of [2.2]paracyclophane-4,13-dicarbaldehyde and its bis-N-phenylimine, resulting in stereoselective formation of the chiral triply-bridged diol and exclusive formation of the meso-diamine. X-Ray investigations of several diols and diamines have been carried out and the structural features of these derivatives are discussed.