[3,3] Sigmatropic Rearrangement of Boron‐Containing Allyl Alcohols: Synthesis of Allyl Addition Reagents

Pietruszka, Jörg; Schöne, Niklas

doi:10.1002/anie.200352210

Cited by 57 publications

(14 citation statements)

References 38 publications

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“…For convenience during the work‐up procedure, the crude products were directly reduced with LiAlH 4 to give the corresponding diols (i.e., 15 and 16 , from 13 and 14 , respectively). The overall yields were moderate (31–65 %), but the enantioselectivity was relatively low compared to that obtained with unsubstituted reagents 4 and 5 (Scheme , R 1 = H) 5a,5d. In contrast to this moderate enantioselectivity, the allyl addition showed complete ( Z ) selectivity (>95 % as detected by NMR spectroscopy), which can be attributed to the pseudo‐axial position of the α substituent in transition states TSA and TSB .…”

Section: Resultsmentioning

confidence: 91%

Importance of the Support Properties for Immobilization or Purification of Enzymes

et al. 2015

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Immobilization and purification of enzymes are usual requirements for their industrial use. Both purification and immobilization have a common factor: they use a solid activated support. Using a support for enzyme purification means having mild conditions for enzyme release and a selective enzyme–support interaction is interesting. When using a support for immobilization, however, enzyme desorption is a problem. The improvement of enzyme features through immobilization is a usual objective (e.g., stability, selectivity). Thus, a support designed for enzyme purification and a support designed for enzyme immobilization may differ significantly. In this review, we will focus our attention on the requirements of a support surface to produce the desired objectives. The ideal physical properties of the matrix, the properties of the introduced reactive groups, the best surface activation degree to reach the desired objective, and the properties of the reactive groups will be discussed.

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Section: Resultsmentioning

confidence: 91%

Importance of the Support Properties for Immobilization or Purification of Enzymes

et al. 2015

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“…124 The absolute configuration of the new reagents was assigned by means of chemical correlation or X-ray structure analysis. The reaction of diastereomers (3S)-and (3R)-20 with benzaldehyde was performed in good yield (78− 91%) and enantiomeric excess (>94% ee).…”

Section: Double Stereoselectionmentioning

confidence: 99%

Diastereoselective Allylation of Carbonyl Compounds and Imines: Application to the Synthesis of Natural Products

2013

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2.2. Chiral Imines and Imine Derivatives 2.2.1. Imines and Imine Derivatives from Chiral Carbonyl Compounds. Chiral α-oxysubstituted aldehydes were used by Kobayashi and co-workers in a three-component reaction with allylboropinacolate and ammonia in ethanol. The corresponding homoallylic primary amines were obtained with good to high syn diastereofacial selectivities (Scheme 5). 20 The precise reaction mechanism was unclear. Preformation of N-Scheme 3 Scheme 4 Scheme 5 Chemical Reviews Review dx.

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“…[7][8][9][10][11][12][13][14] We have recently demonstrated that highly stable reagents of the general type 1 or 2 are readily available via a Johnson rearrangement of the corresponding boron-substituted allyl alcohols. [15][16][17] The derivatives are easy to handle and store, and add highly selectively to a number of aldehydes giving either homoallylic alcohol 3 or 4 with the enantiomeric excess ranging from 92 to >99% (Scheme 1). The formation of the Z-double bond and the configuration of the newly formed stereogenic centers were unambiguously proven by means of chemical correlation.…”

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confidence: 99%

New Enantiomerically Pure Allylboronic Esters in Allyl Additions: Synthesis and NMR Investigation of Intermediates

Pietruszka¹,

Schöne²

2006

Synthesis

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Enantiomerically pure allylboronic esters 1 + 2 with a stereogenic center a to the boron moiety can be obtained by a sigmatropic rearrangement of boron containing allyl alcohols. Allyl additions with the new reagents are highly selective, which was shown via the direct measurement of the diastereoisomeric ratio of the intermediates 5 + 6 by characteristic NMR chemical shifts. The observations are not limited to ester containing reagents, but holds also true for hydrocarbon side-chains (e.g. in 11 + 12) that were readily obtained by reducing the ester.One of the key reactions in organic synthesis is the allyl addition, especially using allylboronic esters; regularly homoallylic alcohols are conveniently formed in high yield and enantiomeric excess. 1-6 Reagents having a stereogenic center in the position a to the boronic ester are less often used since they are more difficult to prepare in enantiomerically pure form. 7-14 We have recently demonstrated that highly stable reagents of the general type 1 or 2 are readily available via a Johnson rearrangement of the corresponding boron-substituted allyl alcohols. [15][16][17] The derivatives are easy to handle and store, and add highly selectively to a number of aldehydes giving either homoallylic alcohol 3 or 4 with the enantiomeric excess ranging from 92 to >99% (Scheme 1). The formation of the Z-double bond and the configuration of the newly formed stereogenic centers were unambiguously proven by means of chemical correlation. The results could also be rationalized by a transition state as shown in Scheme 1 -the substituent in position a to boron is preferentially axial -which is in full agreement with a previous report by Hofmann and Weidmann. 7 A drawback of the procedure was the fact that the enantiomeric excess of homoallylic alcohols was regularly determined -as it is common practice -by forming diastereoisomeric Mosher ester 18,19 (when direct methods fail) and thus only indirectly establishing the stereochemical outcome of the transformation. Obviously, there are two problems associated with the approach: A diastereomeric discrimination of the ester formation must be ruled out and, more importantly, the hydrolysis of the intermediate boric esters (in our case 5 and 6) must occur with similar rates. In many cases this might not be a problem; however, occasionally we observed a rate difference that would lead to incorrect results, even when direct methods to determine the enantiomeric excess were used. An obvious solution to the problem would be the utilization of the formed diastereoisomeric intermediates 5 and 6 that should show distinct differences in their NMR spectra. Hence we decided to start a NMR investigation of the reaction before work-up and especially chromatographic separation.First, we investigated the most simple derivatives 5a and 6a ( Figure 1) and found that almost all signals in the proton NMR (500 MHz) show distinct differences in the Scheme 1 Allyl additions of 1 or 2.

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[3,3] Sigmatropic Rearrangement of Boron‐Containing Allyl Alcohols: Synthesis of Allyl Addition Reagents

Cited by 57 publications

References 38 publications

Importance of the Support Properties for Immobilization or Purification of Enzymes

Importance of the Support Properties for Immobilization or Purification of Enzymes

Diastereoselective Allylation of Carbonyl Compounds and Imines: Application to the Synthesis of Natural Products

New Enantiomerically Pure Allylboronic Esters in Allyl Additions: Synthesis and NMR Investigation of Intermediates

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