A Novel Enantioselective (2<i>Z</i>)-Alk-2-enylation of Aldehydes via an Allyl-Transfer Reaction from Chiral Allyl Donors Prepared from (+)-Isomenthone

Nokami, Junzo; Nomiyama, Kenta; Shafi, Siddiqi M.; Kataoka, K.

doi:10.1021/ol0400140

Cited by 41 publications

(8 citation statements)

References 8 publications

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“…20 The new reagents 11 and 12 were tested by using benzaldehyde, thus leading to the known homoallylic alcohols 13 (83%) and 14 (69%) (Scheme 3). 21,22 The NMR analysis of the intermediate boric esters 15 and 16 was in full agreement with the previous observations: Various protons proved to be diagnostic and showed a distinct difference in both diastereoisomers. Especially useful were protons 1-H (D ppm: +0.13) and 6-H (D ppm: -0.09); again the respective other diastereoisomer could not be detected (ee >95%).…”

Section: Figuresupporting

confidence: 89%

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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Section: Figuresupporting

confidence: 89%

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

Pietruszka¹,

Schöne²

2006

Synthesis

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“…The major isomer of this mixture was examined as an allyl donor to a selection of aldehydes, in the presence of p-toluenesulfonic acid monohydrate as catalyst. 129 Importantly, it was found that the major isomer furnished only the (Z)-olefin of the corresponding α-adduct, while the other isomer gave the corresponding (E)-olefin. The transfer of chirality was perfect, obtaining enantiopure homoallylic alcohols in good yields for the aldehydes used.…”

Section: Scheme 44 Scheme 45mentioning

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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“…The catalytic cross-crotylation method provides highly stereoselective access to (E)-linear alcohols 31. The allyltransfer reaction can be also used for the synthesis of linear (Z)-homoallylic alcohols 38, 48,49 but the method employs a two-to threefold excess of a stoichiometric chiral auxiliary reagent. An alternative approach to linear homoallylic alcohols involves the use of secondary allylmetal reagents 37 (Scheme 7).…”

Section: Scheme 6 Cascade Allylations Using Bifunctional Disilane 32mentioning

confidence: 99%

Developing a Methodology for Catalytic Asymmetric Crotylation of Aldehydes

Рубцов

Malkov

2021

Synlett

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Asymmetric crotylation has firmly earned a place among the set of valuable synthetic tools for stereoselective construction of carbon skeletons. For a long time the field was heavily dominated by reagents bearing stoichiometric chiral auxiliaries, but now catalytic methods are gradually taking center stage, and the area continues to develop rapidly. This account focuses primarily on preformed organometallic reagents based on silicon and, to some extent, boron. It narrates our endeavors to design new and efficient chiral Lewis base catalysts for the asymmetric addition of crotyl(trichloro)silanes to aldehydes. It also covers the development of a novel protocol for kinetic resolution of racemic secondary allylboronates to give enantio- and diastereomerically enriched linear homoallylic alcohols. As a separate topic, cross-crotylation of aldehydes by using enantiopure branched homoallylic alcohols as a source of crotyl groups is discussed. Finally, the synthetic credentials of the developed methodology are illustrated by total syntheses of marine natural products, in which crotylation plays a key role in setting up stereogenic centers.1 Introduction2 Pyridine N-Oxides as Lewis Base Catalysts3 Bipyridine N,N′-Dioxides as Lewis Base Catalysts4 Chiral Allylating Reagents5 Synthetic Applications6 Concluding Remarks

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A Novel Enantioselective (2Z)-Alk-2-enylation of Aldehydes via an Allyl-Transfer Reaction from Chiral Allyl Donors Prepared from (+)-Isomenthone

Cited by 41 publications

References 8 publications

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

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

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

Developing a Methodology for Catalytic Asymmetric Crotylation of Aldehydes

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