Ketones camphor-derived amino

Three-component condensation of silicylaldehyde and two different CH acids to give 2-amino-4//-chromenes, catalysed by base-functionalized ionic liquids, has been investigated experimentally and theoretically. Mechanisms of formation and reaction of camphor-derived amino ketones have been discussed. ... 

The group of Collum, inspired by highly selective acetyUde additions to ketones (see below), performed lithium phenylacetyhde additions to PhCHO, mediated by the camphor-derived amino alkoxide 21 in THF at -78°C [80]. Variations of the alkoxide acetyUde ratio revealed changes in the sense of enantiose-lectivity and the highest enantioselectivity (78% ee) was observed at a ratio of 1 3. 

The groups of Pete and Rau also employed chiral amino alcohols for the enantioselective protonation of simple enols 23a-c that were photochemically generated from 2-/-butyl indanones and tetralones 22a-c by a Norrish type II photoelimination (Scheme 9) [41,42]. Best enantioselectivities were obtained at — 40°C in acetonitrile with 0.1 equivalent of the chiral amino alcohol. In the case of indanone 22a, the selectivity reached 49% ee with (— )-ephedrine ent-18) and could not be further enhanced by the camphor derived inductor 20. With this amino alcohol, enantioselectivities over 80% ee were induced in the case of tetralone 22b. A benzyl substituent in place of the methyl group led to substantial decrease of the selectivity to 47% ee. Linear ketones gave low yields and enantioselectivities around 9% ee. 

Several methods for asymmetric C —C bond formation have been developed based on the 1,4-addition of chiral nonracemic azaenolates derived from optically active imines or enamines. These methods are closely related to the Enders and Schollkopf procedures. A notable advantage of all these methods is the ready removal of the auxiliary group. Two types of auxiliaries were generally used to prepare the Michael donor chiral ketones, such as camphor or 2-hydroxy-3-pinanone chiral amines, in particular 1-phenylethanamine, and amino alcohol and amino acid derivatives. 

One problem in the anti-selective Michael additions of A-metalated azomethine ylides is ready epimerization after the stereoselective carbon-carbon bond formation. The use of the camphor imines of ot-amino esters should work effectively because camphor is a readily available bulky chiral ketone. With the camphor auxiliary, high asymmetric induction as well as complete inhibition of the undesired epimerization is expected. The lithium enolates derived from the camphor imines of ot-amino esters have been used by McIntosh s group for asymmetric alkylations (106-109). Their Michael additions to some a, p-unsaturated carbonyl compounds have now been examined, but no diastereoselectivity has been observed (108). It is also known that the A-pinanylidene-substituted a-amino esters function as excellent Michael donors in asymmetric Michael additions (110). Lithiation of the camphor... 

Initial studies [26] carried out with enol carbonates A or P-keto esters B afforded ketones D in high yields and selectivities up to 75% ee [27], using ephedrine or a P-amino alcohol derived from camphor. Surprisingly, cinchona alkaloids bearing the required P-amino alcohol moiety were not tested. It was necessary to wait till 2001 and later for publications describing the use cinchona alkaloids in these reactions, either the natural products or some analogues. 

Various glycine-derived imines of camphor and other chiral ketones or aldehydes have been alkylated in a diastereoselective maimer to give nonracemic a-amino acids after the cleavage of the auxiliary [24]. A more recent concept for the alkylation of a glycinamide-derived enolate developed by Dixon and coworkers links the chiral auxiliary to the a-nitrogen atom under the form the tetrahydropy-ran 35, available from camphor in a three-step protocol. Upon deprotonation with LiHMDS, a cis-configured enolate is assumed to form wherein the metal is chelated by the tetrahydropyranyl oxygen atom. The treatment of the enolate... 

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