Asymmetric Metathesis Dimerization/Desymmetrization of C _s ‐Symmetric Divinylferrocenes: Enantioselective Deactivation of Vinyl Groups and Subsequent Kinetic Resolution of

ABSTRACT

Asymmetric metathesis dimerization/desymmetrization (AMD/DS) reaction on C _s ‐symmetric planar‐prochiral divinylphosphaferrocene/divinylferrocene substrates 1 was realized in the highly enantioselective fashion. For the substrates having a proper substituent in the position adjacent to the vinyl groups in 1 , the molybdenum‐alkylidene precatalyst coordinated with either ( R )‐ or ( S )‐3,3'‐bis(diphenylmethyl)‐5,5',6,6',7,7',8,8'‐octahydro‐2,2'‐binaphtholate ( L1 ) was capable of distinguishing between the two enantiotopic vinyl groups in 1 , and facilitated the AMD reaction at one of the two vinyl groups predominantly providing the corresponding planar‐chiral metathesis dimer 2 in >99% ee. The presence of a substituent neighboring to the vinyl group was critical for the successful AMD/DS reaction, and both enantio‐ and chemoselectivities were poor without it. The reactions using an achiral or a racemic molybdenum‐alkylidene precatalyst did not halt at the dimerization stage and proceeded further to furnish the oligomers/polymers through the acyclic diene metathesis polymerization (ADMET) pathway. The excellent enantio‐ and chemoselectivities in the present AMD/DS process stems from the following two factors: (i) the highly enantioselective deactivation of one of the two enantiotopic vinyl groups in 1 , which prevents the dimers 2 from oligomerizing/polymerizing, and (ii) the subsequent kinetic resolution (KR) on the initially formed planar‐chiral dimeric products 2 , which predominantly consumes the minor enantiomers/diastereomers through ADMET.