Synthesis of pyranotropanes via enantioselective deprotonation strategy

Majewski, Marek; Łaźny, Ryszard

doi:10.1016/s0040-4039(00)73063-2

Cited by 31 publications

(5 citation statements)

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“…ZnCl 2 (∼0.4 equiv) was also efficiently used as additive for chiral Li amide-mediated asymmetric enolizations of ketones. , By studying the impact of Li salts on the deprotonation of cyclic ketones (2- tert -butyl-2-methyl-1,3-dioxan-5-one and tropinone) using chiral Li amides, Majewski and co-workers in general observed higher enantioselectivities in the presence of LiCl and LiBr (1–2 equiv) but no change using LiClO 4 and LiI . In the course of the synthesis of tropane alkaloids, Majewski and Lazny observed that the enantioselectivity of the chiral Li amide-mediated deprotonation of tropinone is dependent on the LiCl amount (Schemes and ) …”

Section: Reactions Of Maas Involving Base Ligand Transfer Processes (...mentioning

confidence: 99%

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

2013

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6. Conclusion 7706 Author Information 7706 Biographies 7707 Acknowledgment 7707 Abbreviations Used 7707 References 7708the corresponding allyl-and propargylchromium reagents that further react with a variety of electrophiles to afford the corresponding adducts in high yields. 102 Bu 6 CrLi 3 similarly behaves as a formal two-electron reductant with ketones and esters bearing a leaving group at the α-position to produce enolates that are intercepted with a variety of electrophiles with high selectivities (Table 8). 103 Such enolates are also capable of reacting with oxiranes to afford γand β-hydroxy esters, depending on the Lewis acid used as promoter. 2143.2.2. Two-Electron Transfers from M,Mn-HeteroMAAs (M = Li, MgX). In 1976, Cahiez et al. disclosed the possible reduction in THF of alkenyl bromides or iodides, as well as aryl chlorides or bromides, using i-PrMgCl in the presence of a catalytic amount of MnCl 2 . 215 The authors proposed the in situ formation of unstable i-Pr 3 MnMgCl and its decomposition by β-elimination to H 3 MnMgCl; reaction of the latter with the halide would then afford an unstable Mn(IV) intermediate, able Scheme 23 Scheme 24 Scheme 21 Scheme 22

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Section: Reactions Of Maas Involving Base Ligand Transfer Processes (...mentioning

confidence: 99%

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

2013

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“…The presence of LiCl is crucial to obtain a good ee in the case of the external quench. The base is thus generated by treating the easily available hydrochloride salt of 18 with 2 equiv of butyllithium . As shown in Scheme , ketone 16 smoothly afforded silyl enol ether 17 in 54% yield and 97% ee for the internal quench and 80% yield and 94% ee for the external quench .…”

Section: Resultsmentioning

confidence: 99%

Enantioselective Synthesis of the C1−C11 Fragment of Bafilomycin A₁Using Non-Wittig and Desymmetrization Strategies

et al. 2003

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The synthesis of the C1-C11 fragment 33 of bafilomycin A(1) was achieved. Intermediate ketone 16 was prepared in six steps from 4-oxopimelate 13. Desymmetrization of this ketone using Koga's chiral base followed by TMSCl quench furnished silyl enol ether 17 with excellent enantioselectivity. Further elaboration led to C5-C11 aldehyde 24, which was coupled with sulfone 3 to give lactone 25 in very good yield. The subsequent reductive elimination created the E-trisubstituted C4-C5 olefin with a 13:1 selectivity. The E C2-C3 double bond was then installed by methanol elimination, and compound 33 was obtained after a few functional group manipulations and a Negishi methyl zirconation.

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“…Koga has reported full experimental details for the preparation of his phenylglycine-derived bases,65 and Majewski has used this type of base with LiCl as an additive to deprotonate tropinone in up to 92% ee. 66 The symmetrical cyclopentene epoxide 48 has been deprotonated and ring opened in 95% ee using the readily available dilithiated norephedrine 49 to give 50 (Scheme 25), 67 which is an intermediate for the sythesis of carbovir. Similar work on the silyl-protected trans-epoxide using a prolinederived base has also been reported, including the conversion of the product into (-)-ca~bovir.~~ The same group has also used catalytic amounts of the same base, with a stoichiometric amount of LDA, to open cyclohexene epoxide in 75% ee with 0.2 equiv.…”

Section: Miscellaneous Uses Of Chiral Auxiliariesmentioning

confidence: 99%

Asymmetric processes

Regan¹

1997

Contemp. Org. Synth.

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Synthesis of pyranotropanes via enantioselective deprotonation strategy

Cited by 31 publications

References 14 publications

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

Enantioselective Synthesis of the C1−C11 Fragment of Bafilomycin A₁Using Non-Wittig and Desymmetrization Strategies

Asymmetric processes

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Synthesis of pyranotropanes via enantioselective deprotonation strategy

Cited by 31 publications

References 14 publications

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 2. Syntheses and Reactivities of Homo/HeteroMAAs

Enantioselective Synthesis of the C1−C11 Fragment of Bafilomycin A1Using Non-Wittig and Desymmetrization Strategies

Asymmetric processes

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Enantioselective Synthesis of the C1−C11 Fragment of Bafilomycin A₁Using Non-Wittig and Desymmetrization Strategies