Asymmetric synthesis with (S)-(-)butyl-tert-butylcarbinyl benzoylformate

Abstract

We have found that the reaction of methylmagnesium iodide in ether with (S)-( -)-«-butyl-ier?-butylcarbinyl benzoylformate preferentially attacks the re face of the -keto group to give a 7.5% excess of the (S)-atrolactate diastereomer. Based on the premise that ieri-butyl acts as a larger group than «-butyl this result is in accord with Prelog's generalization concerning the course of this reaction. In tetrahydrofuran, however, the stereoselectivity was essentially zero. On the other hand, reduction of this same substrate by lithium tri-ieri-butoxyaluminohydride in either tetrahydrofuran or ether resulted in preferential attack on the si face of the a-keto group to give the (if)-mandelate diastereomer in excess (13 and 8%, respectively). This reversal in stereoselectivities between the Grignard addition and lithium tri-ierf-butoxyalummohydride reductions emphasizes the caution necessary in extrapolating stereoselectivities from one seemingly closely related reaction to another, especially when the stereoselectivities are low and the nature of steric differences are not clearly evident. Stereochemical analysis of the reaction mixtures was greatly facilitated by the use of the nmr enantiomer reagent, amethoxy-a-trifluoromethylphenylacetic acid, alone and in conjunction with europium nmr shift reagents.

An efficient chiral phosphorus derivatizing agent for the determination of the enantiomeric excess of chiral alcohols and amines by 31P NMR spectroscopy

“…The enantiomeric excess determination by means of NMR spectroscopy can be carried out using the chiral lanthanide shift reagent [4], chiral complexing reagents [5], and chiral derivatizing agents (CDA) [6]. However, at present, determination of ee using CDA is the most widely used NMR spectroscopy technique, as discrete diastereomers show chemical shift nonequivalences, δ, that are typically five times higher than for the use of other chiral reagents [6].…”

“…However, at present, determination of ee using CDA is the most widely used NMR spectroscopy technique, as discrete diastereomers show chemical shift nonequivalences, δ, that are typically five times higher than for the use of other chiral reagents [6]. The most widely used CDA is ␣-methoxy-␣-(trifluoromethyl)benzeneacetic acid (MTPA) introduced by Mosher in 1969 [7].…”

Analysis of an Asymmetric Addition with a 2:1 Mixed Lithium Amide/n-Butyllithium Aggregate

“…Absolute stereochemistry was assigned in accord with the published value of optical rotation. 27 (S)-R-Butyl-2-furanmethanol: [R] 24 D -10.4 (c 1.00, CHCl 3 ), 74% ee. Absolute stereochemistry was assigned in accord with the published value of optical rotation.…”

Application of chiral lanthanide-induced shift reagents to optically active cations: the use of tris[3-(trifluoromethylhydroxymethylene)-(+)-camphorato]europium(III) to determine the enantiomeric purity of tris(phenanthroline)ruthenium(II) dichloride

“…spectroscopy using chiral shift reagents. [1][2][3][4] Although lanthanide-induced shift reagents were first used to study cations in 1973, 5 chirallanthanide-induced shift reagents have been used only with neutral species. We report the application of chiral lanthanide-induced shift reagents to optically active cations.…”

“…9 x 10-3 M) containing Eu(tfc) 3 (2.7 x 10-2 M) in CD 2 Cl 2 , we were able to distinguish between the two enantiomers and determine the enantiomeric purity of the sample. t The resulting spectrum at 200 MHz is shown in Figure 1(a) and is compared to that of the same solution in the absence of Eu(tfc) 3 in Figure l(b).…”