Stereoselective conjugate addition of lithium and titanium enolates to γ - alkoxy enones

Bernardi, Anna; Marchionni, Chiara; Novo, Barbara; Karamfilova, K.; Potenza, Donatella; Scolastico, Carlo; Roversi, Pietro

doi:10.1016/0040-4020(96)00028-2

Cited by 8 publications

(2 citation statements)

References 28 publications

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“…The reaction with the chiral enone given in Scheme leads to the 2,3-anti-3,4-anti isomer (78% selectivity) using the mixed enolate, whereas the 2,3-syn-3,4-anti isomer (82% selectivity) is formed from the Li enolate . The authors proposed an inverse demand Diels–Alder cycloaddition to explain the different stereochemical behavior of the mixed Li,Ti enolate …”

Section: Reactions Of Maas Involving Nucleophile Ligand Transfer Proc...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 Nucleophile Ligand Transfer Proc...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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“…88(a) The addition of 1 mol equivalent of Ti(OiPr) 4 to Li enolates (formed with LDA) and subsequent successful addition of the enolates to a variety of systems has been reported. When the titanium enolate of 7 was prepared according to the described procedure, 89 and then reacted with benzaldehyde, a reasonably good 59% yield was obtained, with a syn:anti ratio of 4:1. Although the reaction was tried using aldehyde (S)-160 (described below) these conditions were not pursued.…”

Section: Lithium Enolates -Lda and Litmpmentioning

confidence: 99%

Towards a Total Synthesis of Peloruside A and the Preparation of Selected Inositol Derivatives

Baars¹

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<p>This thesis covers two broad areas of work under the general theme of the synthesis of bioactive and/or synthetically useful compounds based on natural products or deriving from the chiral pool. Chapters one, two and three focus on the marine secondary metabolite peloruside A (1), which has been shown to stabilise microtubules during mitosis and hence cause apoptosis (cell death) in a similar manner to the very successful anticancer drug Taxol. A synthetic program with the aim of devising a total synthesis was initiated at Victoria University of Wellington after peloruside A's discovery in 1999. Four synthetic disconnects were identified in the retrosynthetic analysis of peloruside A: to give the C-l to C-2 fragment; the C-3 to C-7 fragment; the C-8 to C-11 fragments; and the C-12 to C-24 fragment. The C-7 to C-8 bond was to be formed via an asymmetric aldol reaction to give the pyranose ring fragment (highlighted in blue). In this thesis, the synthesis of the C-3 to C-7 fragment is described. A1do1 reactions with the C-8 to C- 11 ketone have been investigated, and subsequent progress towards the assembly of the pyranose ring fragment is presented. Chapters four, five, six and seven describe the preparation of selected synthetically and biologically useful derivatives of the commercially available inositols, quebrachitol (L-chiro-inositol-2-methyl ether) and myo-inositol. The butane di-acetal (BDA) derivatives 293, 300, and 301 (as well as acetylated and methylated derivatives thereof) were prepared during work directed towards the synthesis of the inositol core of a phosphatidylinositol manno-oligosaccharide (PIM-6) isolated from Mycobacterium bovis and M. smegmatis. Quebrachitol derivatives 305, 306 and 307 were prepared and subsequently tested against myoinositol (the optimal competitor) in biological uptake assays of the microorganisms, Candida albicans and Leishmania donovani. For both microorganisms, the mono- and di-O-methylated L-chiro-inositol derivatives 307 and 305, as well as quebrachitol, gave significant inhibition results, with P values from P < 0.001 to P < 0.05 for paired-sample t-test analyses, i.e.99.9% to 95% confidence for significant inhibition, respectively. The benzoylated derivative 306 did not induce any inhibition of myo-inositol uptake. Myo-inositol is the most abundant of the inositols in nature and is readily available. However, as it is a meso compound, one of the key challenges in the use of myoinositol as a synthetic precursor is an efficient resolution method. The formation of myo-inositol camphanylidene acetal 269a is one successful solution, and work done in an attempt to better understand the selectivity of the reaction is reported here. Also, process development work was done to adapt the preparation so that it was suitable for scale-up, and a subsequent large scale synthesis of the acetal was undertaken. Previously unpublished X-ray crystal structures were obtained for 269a and, for two of the diastereomeric impurities of the reaction.</p>

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Synthesis of (−)‐(E,S)‐3‐(Benzyloxy)‐1‐Butenyl Phenyl Sulfone Via a Horner‐Wadsworth‐Emmons Reaction of (−)‐(S)‐2‐(Benzyloxy)Propanal

Enders¹,

Berg²,

Jandeleit³

2003

Organic Syntheses

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(−)‐(E,S)‐3‐(Benzyloxy)‐1‐butenyl phenyl sulfone R (S)‐Ethyl 2‐hydroxy propanoate [(S)‐ethyl lactate] I (−)‐(S)‐Ethyl 2‐(benzyloxy) propanoate (−)‐(S)‐2‐(Benzyloxy)propanal P (−)‐(E,S)‐3‐(Benzyloxy)‐1‐butenyl phenyl sulfone

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Stereoselective conjugate addition of lithium and titanium enolates to γ - alkoxy enones

Cited by 8 publications

References 28 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

Towards a Total Synthesis of Peloruside A and the Preparation of Selected Inositol Derivatives

Synthesis of (−)‐(E,S)‐3‐(Benzyloxy)‐1‐Butenyl Phenyl Sulfone Via a Horner‐Wadsworth‐Emmons Reaction of (−)‐(S)‐2‐(Benzyloxy)Propanal

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