Kinetic resolution reactions With chiral DMAP

Carbon dioxide is one of the most abundant carbon resources on earth. It reacts with an epoxide to give either a cyclic carbonate or a polycarbonate depending on the substrates and reaction conditions. Kinetic resolution of racemic propylene oxide is reported in the formation of both cyclic carbonate and polycarbonate. The fe ei value defined as ln[l-(conversion)(l+%ee)]/ln[l-(conversion)(l% ee)] reached 6.4 or 5.6 by using a Co(OTs)-salen complex with tetrabutylammonium chloride under neat propylene oxide or using a combination of a Co-salen complex and a chiral DMAP derivative in dichloromethane, respectively. 

In 1993, Vedejs et al. [5,6] showed that tributylphosphine is a potent catalyst for the acylation of alcohols by acetic and benzoic anhydrides as efficient as 4-(di-methylamino)pyridine DMAP [7,8]. However, the DMAP catalyst is more versatile since it presents catalytic activity in the reaction of alcohols with a larger variety of electrophiles. Due to these properties, Fu [9] realized the design and synthesis of a new family of chiral nucleophilic catalysts illustrated by the planar-chiral DMAP derivative I which is a very efficient catalyst in different enantioselective reactions such as addition of alcohols to ketenes [10], rearrangement of O-acylated azalactones [11], and kinetic resolution of secondary alcohols [12-14]. 

With a parallel kinetic resolution, the two reactions should not interfere with one another. In the example above, both reactions were acylations but the use of stoichiometric reagents meant that the right acylating group was attached to the right enantiomer. Even here, Vedejs does not rule out a small amount of leakage between the paths (once the chiral DMAP is liberated it can get in on the act with the other pathway). A PKR becomes more difficult if, in addition to the reactions being related, they are also catalytic. 

For example, Fu and co-workers have shown that planar chiral ferrocenyl DMAP derivative 118 catalyzes the kinetic resolution of arylalkylcarbinols with excellent efficiency (S = 32-95) [3]. As a representative example, the preparative-scale reaction depicted in Scheme 19 provides o-tolylmethylcarbinol 116 and its acetylated derivative 117 in >90% ee using low catalyst loadings (0.5mol%) and giving high catalyst recovery (89%). ... 

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