Aldol anfi-selective

Aldol reactions. Lithium enolates of BINOL esters react with carbonyl compounds in an anfi-selective fashion. One method for the preparation of such BINOL esters is by reaction of the dibutyltin BINOLate with acid chlorides. ... 

Aldol condensation. The ultrasound-promoted reaction between silyl enol ethers and aldehydes on alumina surface is anfi-selective. 

SCHEME 2.113 Typical procedure for anfi -selective Masamune-Abiko aldol reaction. 

The real catalytic potential of primary amino acids was disclosed by Barbas in the asynunetric direct aldol reactions of a-hydroxyketones such as hydroxyacetone and dihydroxyacetone (DHA) catalyzed by 0-t-Bu-L-threonine 14 [15]. The reactions gave unprecedentedly 5yn-selectivity, to note that most chiral secondary amine catalysts like L-proline are anfi-selective in these reactions (Scheme 5.4). A Z-enamine was proposed to account for the iyn-diastereoselectivity and in this model the secondary enamine A-H would participate in intramolecular hydrogenbonding with OH group, contributing the Z-enamine (Scheme 5.4). Very recently. 

Non-Evans Aldol Reactions. Either the syn- or onri-aldol adducts may be obtained from this family of imide-derived eno-lates, depending upon the specific conditions employed for the reaction. Although the illustrated boron enolate affords the illustrated jyn-aldol adduct in high diastereoselectivity, the addition reactions between this enolate and Lewis acid-coordinated aldehydes afford different stereochemical outcomes depending on the Lewis acid employed (eq 35). Open transition states have been proposed for the Diethylaluminum Chloride mediated, anti-selective reaction. These anfi-aldol reactions have been used in kinetic resolutions of 2-phenylthio aldehydes. ... 

An important contribution to the field of direct aldol reaction was put forward by MacMillan who reported on the enantioselective direct cross aldol reaction (Scheme 2.119) [31]. Two aldehydes are brought to reaction with 10mol% prohne to produce selectively the anfi-aldol product. If different aldehydes are used, the one that contains a sterically more crowded side chain acts as the carbonyl component, whereas simple aldehydes, in most cases acetaldehyde or even acetone, act as nucleophiles. The advantage of such organocatalytic aldol reactions is the fact that aldehydes can be used, which is practically prohibited if enolates or... 

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