Naphthyl aldimine

However, the enantioselectivities remained unsatisfactory. In 2003, Park and coworkers designed new substrates to increase the enantioselectivities of a,a-diallq l-ot-amino acids. After systematic optimisation of the aldimine substrates and reaction conditions, allqrlation of the 2-naphthyl aldimines of alanine tert-butyl esters (17) with rubidium hydroxide and the electronically optimised Cinchona catalyst 8d, at 35 °C, was shown to afford the corresponding (5)-a-allqrl-alanines, 18, with up to 96% enantiomeric excess (Scheme 16.10). ... 

Two years after the discovery of the first asymmetric Br0nsted acid-catalyzed Friedel-Crafts alkylation, the You group extended this transformation to the use of indoles as heteroaromatic nucleophiles (Scheme 11). iV-Sulfonylated aldimines 28 are activated with the help of catalytic amounts of BINOL phosphate (5)-3k (10 mol%, R = 1-naphthyl) for the reaction with unprotected indoles 29 to provide 3-indolyl amines 30 in good yields (56-94%) together with excellent enantioselec-tivities (58 to >99% ee) [21], Antilla and coworkers demonstrated that A-benzoyl-protected aldimines can be employed as electrophiles for the addition of iV-benzylated indoles with similar efficiencies [22]. Both protocols tolerate several aryl imines and a variety of substituents at the indole moiety. In addition, one example of the use of an aliphatic imine (56%, 58% ee) was presented. 

Aza-MBH reactions of alkyl or aryl acrylates, as well as acrolein, required higher reaction temperatures than were required with MVK or EVK. While phenyl- or naphthyl acrylates afforded products in CH2C12 with ee-values up to 69%, the best solvent in the addition of acrolein to activated aldimines proved to be THF (Scheme 5.25) [100]. 

Takahashi and Suzuki (equation 4). The use of methyl-, benzyl- and 2-propenyl-lithium gave exclusive 1,2-addition. Demonstration that this methodology can be extended to 2-naphthyl, 3-pyridyl and 3-quino-lyl aldimines (paralleling oxazoline chemistryhas not been reported. 

Deprotection of Fmoc-amino acid Wang resins under standard conditions yielded the polymer-bound amino acids 1. Condensation with 3,4-dichlorobenzaldehyde gave aldimines 2. Subsequent alkylation with electrophiles such as benzyl-, naphthyl- or allylbromide in the presence of 2-[(l,l-dimethylethyl)imino]- W,N-diethyl - 2,2,3,4,5,6- hexahydro-1,3-dimethyl-1,2,3-diazaphosphorin-2(lH)-amine (BEMP) gave the disubstituted aldimines 3. Transketalisation with hydroxylamine hydrochloride yielded the free amine 4 which was acylated and cleaved to give the final product 5 in good yields and purities. 

In 2007, Feng et al. reported an efficient self-assembled catalytic system for the addition of trimethylsilyl cyanide to imines. The combined use of cinchonine (27), achiral 3,3 -(2-naphthyl)-2,2 -biphenol (28), and titanium tetra-isopropoxide gave an efficient catalyst for aldimines and ketimines (Scheme 7.19). Cinchonine induces a chiral environment around the titanium atom by fixing a stable chiral configuration to the biphenol ligand, and also activates hydrogen cyanide, generated in situ. In addition to trimethylsilyl cyanide, safer ethyl cyanoformate can be used with similar results. 

---