Enantioselective ethylation

Wally et al.115 report a homoannularly bridged hydroxyamino ferrocene (+)-123 as an efficient catalyst for enantioselective ethylation of aromatic or aliphatic aldehydes. 

When considering the easy recovery and reuse of chiral catalysts, or simple separation process of the product from chiral catalyst, polymer-supported catalysts are very attractive [1,3]. For the enantioselective ethylation using dialkylz-inc, Frechet and Itsuno s group and our group developed polystyrene-supported amino alcohols [1]. 

In 1997 Pu reported a new type of main chain chiral polymer derived from BINOLs [24]. Polymer 16 catalyzed enantioselective ethylation using diethylzinc to give secondary alcohols in up to 94% ee. It is noteworthy that 16 is a derivative of chiral BINOL but the addition of Ti(IV) is unnecessary unlike other reported chiral monomeric diols. In 1998, Pu reported that polymer 17, which has a phenylene spacer between two BINOL moieties, results in better ees of up to 98% [24]. 

Zirconium-Catalyzed Enantioselective Ethyl- and Higher Alkylalumination of Unactivated Alkenes... 

Enantioselective ethylation of /V-diphenylphosphinylimine using DBNE as a chiral ligand213... 

Enantioselective Conjugate Addition to Prochiral Enones of Organometallic Reagents Modified with Ephedrine. Enantioselective conjugate addition to 2-cyclohexenone with chiral organo(alkoxo)cuprates [MCu(OR )R] has been studied. When the cuprate is prepared from the lithium alkoxide of ephedrine, Phenyllithium, and Cul, 3-phenylcyclo-hexanone with 50% ee is obtained. The enantioselectivity reaches 92% ee in enantioselective ethylation when a chiral diamino alcohol derived from ephedrine is employed (eq 13). ... 

In the presence of a catalytic amount of a chiral P-amino alcohol, the enantioselective ethylation of benzaldehyde with diethylzinc affords enantiomerically en-... 

The chiral catalysts 1 to 4 are highly enantioselective in the addition of di(prira-alkyl)zincs to aromatic aldehydes. (IS, 2i )-iV,iV-dibutylnorephedrine [1 (DBNE)] [5] possesses the advantage of its utility as a highly enantioselective catalyst even for the alkylation of aliphatic aldehydes to afford aliphatic sec-alcohols with up to 93% ee [5]. DBNE is also an appropriate chiral catalyst for the addition of diisopropylzinc [di(sec-alkyl)zinc] (98% ee) [15]. (S)-Diphenyl(l-meth-ylpyrrolidin-2-yl)methanol [2 (DPMPM) [6] catalyzes the enantioselective ethylation of aromatic aldehydes to afford almost enantiomerically pure sec-alcohols... 

The catalytic cycle for enantioselective ethylation of aldehyde TM le is presented in Scheme 1.13. 

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