Synthesis of 3‐Deoxy‐<scp>D</scp>‐<i>manno</i>‐2‐octulosonic Acid (KDO)

Schmidt, Richard R.; Betz, Rainer

doi:10.1002/anie.198404301

Cited by 36 publications

(3 citation statements)

References 11 publications

(1 reference statement)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The most logical and simple synthetic approaches to 3-deoxy-2-ulosonic acids VI in general are those based on biomimetic pathways, i.e., the enzyme-catalyzed couplings of an aldehydo sugar V with a pyruvic acid derivative or the chemical coupling of the same aldehydo sugar with a surrogate for the pyruvate unit (Scheme ) . The Dondoni group developed two synthetic routes leading to these higher sugars based on the thiazole−aldehyde synthesis.…”

Section: 4 3-deoxyulosonic Acidsmentioning

confidence: 99%

Thiazole-Mediated Synthetic Methodology

2004

View full text Add to dashboard Cite

Section: 4 3-deoxyulosonic Acidsmentioning

confidence: 99%

Thiazole-Mediated Synthetic Methodology

2004

View full text Add to dashboard Cite

“…Acrylic acid derivatives with a heteroatom (N, O, S, Hal) at C-3 can be cleanly deprotonated at this position with BuLi or LDA at low temperatures [329,[333][334][335][336][337][338] (Scheme 5.37). Some of these anions rearrange to the a-metalated acrylates on warming [329], but can also decompose (see Section 5.4.7).…”

Section: Vinylic Carbanionsmentioning

confidence: 99%

The Alkylation of Carbanions

Dörwald

2004

Side Reactions in Organic Synthesis

View full text Add to dashboard Cite

The deprotonation of organic compounds by strong, non-nucleophilic bases followed by C-alkylation with a suitable electrophile has become one of the most predictable and straightforward methods for formation of C-C bonds. The popularity of this chemistry is also a consequence of the often-seen close resemblance of feasible structural modifications by a deprotonation/alkylation strategy to an unsophisticated retrosynthetic analysis of a given target compound. Other reactions, which involve, for instance, substantial rearrangement of the carbon framework (e.g. Cope rearrangement, fragmentations, ring contractions or enlargements) are usually more difficult to take into account during retrosynthetic analysis.LDA and related, sterically hindered, lithium dialkylamides, first investigated by Levine [1], have completely replaced the more nucleophilic sodium amide, which had been the base of choice for many years [2]. Because the reactivity of an organometallic compound depends to a large extent on its state of aggregation (i.e. on the solvent and on additives) and on the metal, transmetalation of the lithiated intermediates and the choice of different solvents and additives emerged as powerful strategies for fine-tuning the reactivity of these valuable nucleophiles.In this chapter the alkylation of carbanions with simple carbon electrophiles will be discussed, with special emphasis on the structure-reactivity relationship of the carbanion and on side reactions. In this context the term "carbanion" refers to an intermediate prepared by in-situ deprotonation of an organic compound, followed by optional cation exchange (transmetalation), which tends to be alkylated at carbon by soft electrophiles such as MeI or PhCHO. This type of reactivity is characteristic of enolates with an ionic M-O bond or for organometallic compounds with a strongly polarized or ionic M-C bond, M typically being an alkali metal, Mg, Cu, or Zn. Carbanions can, alternatively, also be prepared by halogen-metal exchange [3-8], sulfoxide-or sulfone-metal exchange [9-13], or by transmetalation of stannanes. The most suitable reagents for performing such metalating exchange reactions are organometallic compounds with a metal-bound secondary or tertiary alkyl group, such as tBuLi, sBuLi, iPr 2 Zn [14, 15], or iPrMgHal [6]. These reagents are thermodynamically less stable than organometallic compounds with primary alkyl 5 146 Scheme 5.1. Approximate relative rates of proton transfer in water at thermoneutrality (DpK a = 0) [35, 39, 51]. 147 Scheme 5.2. The effect of fluorine on the acidity of organic compounds [24, 62-65]. 148 Scheme 5.3. Dependence of the reactivity of carbanions on their basicity [68, 72-74]. Regioselectivity of Deprotonations and AlkylationsThe organic chemist is occasionally confronted with the problem that a compound has several differrent X-H groups of similar pK a . If only one of these is to be alkylated, one option would be to perform a regioselective deprotonation. This can sometimes be achieved by exploiting small differences be...

show abstract

“…91 However, the use of systems such as racemic 185 for the preparation of cyclopentenones 186 afforded rather low stereocontrol (2:1 diastereomer ratio) (Scheme 41). 92 Similarly, β-lithiated β-amino-substituted acrylate derivatives type 181 (X ) R 2 N; Z ) CO 2 Me or CO 2 -Et) have also been employed for the synthesis of tetronates, 93 butenolides, 94 and cyclopentenones, 94 as well as β-lithiated β-amino- 95,96 or thio-substituted 97 acrylamides. Even (E)-cinnamic esters (181, X ) Ph; Z ) CO 2 Et) can be metalated at the β-position with (E)-N-Isopropyl-3-(p-toluenesulfonyl)acrylamide ( 128), prepared as mentioned previously from Nisopropylacrylamide by a tandem iodosulfonylationdehydroiodination reaction, 99 could give a reagent type 181 (X ) p-TolSO 2 ; Z ) CONLiR) which uses the stabilizing and directing effect of the sulfonyl group in metalation reactions.…”

Section: A Rβ-unsaturated Unprotected Carbonyl Compoundsmentioning

confidence: 99%