Boron-Mediated Asymmetric Aldol Reactions

Favored by small L, good leaving group (i.e. OTf), bulky amine base 

Favored by large L, poor leaving group (i.e. Cl), small amine base 

In order to circumvent this general lack of aldol selectivity with chiral aldehydes, one typically needs to employ a chiral enolate 

Having accomplished one merger, only a final macrolactoni-zation now stood in the way of a completed synthesis of swinholide A (1). Before that step could be executed, however, the protecting groups guarding oxygen functions at C-1 and C-21 in 138 had to be removed. Although such operations are usually cursory events, the complexity of swinholide A (1) 

For a general review on cancer therapies using natural products, see J. Mann, Nature Reviews Cancer 2002, 2, 143. 

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ANTI-SELECTIVE BORON-MEDIATED ASYMMETRIC ALDOL REACTION OF CARBOXYLIC ESTERS SYNTHESIS OF (2S, 3R)-2,4-DIMETHYL-1,3-PENTANEDIOL... 

Table Boron-Mediated Asymmetric Aldol Reactions...

Dialkylboron trifluoromethanesulfonates (triflates) are particularly useful reagents for the preparation of boron enolates from carbonyl compounds, including ketones, thioesters and acyloxazolidinones.4 Recently, the combination of dicylohexylboron trifluoromethanesulfonate and triethylamine was found to effect the enolization of carboxylic esters.5 The boron-mediated asymmetric aldol reaction of carboxylic esters is particularly useful for the construction of anti (3-hydroxy-a-methyl carbonyl units.6 The present procedure is a slight modification of that reported by Brown, et al.2... 

ANTI-SELECTIVE BORON-MEDIATED ASYMMETRIC ALDOL REACTION OF 116... 

Anti-selective Boron-mediated Asymmetric Aldol Reaction of Carboxylic Esters. 

Stoever, M, Luetzen, A, KoeU, P, New glyco-oxazolidin-2-ones as chiral auxiliaries in boron-mediated asymmetric aldol reactions. Tetrahedron Asymmetry, 11, 371-374, 2000. 

BORON-MEDIATED ASYMMETRIC ALDOL REACTIONS FOR THE CONVERGENT SYNTHESIS OF NATURAL PRODUCTS... 

Abiko A, Liu JF, Masamune S. The anti-selective boron-mediated asymmetric aldol reaction of carboxylic esters. J. Am. Chem. Soc. 1997 119 2586 2587. 

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