STEREOSELECTIVE TITANIUM-MEDIATED ALDOL REACTIONS OF MENTHYL ACETATE ENOLATES, AND ALLYLATIONS WITH BENZALDEHYDE
The enolates of (+)- and (-)-menthyl acetate, formed by transmetallation from lithium with chloro(cyclopentadienyl)bis(1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranosato-O3)titaniUM [CpTi(DAGO)2Cl] (1), react with benzaldehyde from the Re-face with high stereoselectivities (95 and 92% diastereomeri...
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Published in | Australian journal of chemistry Vol. 46; no. 5; pp. 583 - 591 |
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Main Authors | , , , , , , , |
Format | Journal Article |
Language | English |
Published |
COLLINGWOOD
C S I R O PUBLICATIONS
01.01.1993
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Subjects | |
Online Access | Get more information |
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Summary: | The enolates of (+)- and (-)-menthyl acetate, formed by transmetallation from lithium with chloro(cyclopentadienyl)bis(1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranosato-O3)titaniUM [CpTi(DAGO)2Cl] (1), react with benzaldehyde from the Re-face with high stereoselectivities (95 and 92% diastereomeric excess) when 12-crown-4 is used during the transmetallation. Use of the chiral cyclopentadienyltitanium-alpha,alpha,alpha',alpha'-tetraaryl-2,2-dimethyl-1,3-dioxolan-4,5-dimethanol (TADDOL) complex (3) gives lower diastereoselectivities (58 and 40%) but the Si-face of benzaldehyde is attacked preferentially.
Transmetallation of the 2-methylprop-2-enyl moiety to CpTi(DAGO)2Cl gives an allyltitanium reagent (2) which reacts with benzaldehyde from the Re-face with 88% enantiomeric excess. |
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ISSN: | 0004-9425 |
DOI: | 10.1071/CH9930583 |