New Mechanistic Proposal for Some Heptamolybdate‐Ion‐Catalyzed Isomerizations

Klaić, Branimir; Raza, Zlata; Sanković, Mauricio; Šunjić, Vitomir

doi:10.1002/hlca.19870700107

Cited by 17 publications

(1 citation statement)

References 17 publications

(8 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Reaction of d-galactal with anisaldehyde dimethyl acetal was catalysed Scheme 4.5 Synthesis of carbonate 304 Alternative means of obtaining 2,3-unsaturated substrates were then investigated. It has been reported that the use of ammonium heptamolybdate in glycal isomerisation may provide access to 2,3-unsaturated sugars 129. This reaction was carried out in acetic anhydride, and proceeded very quickly: after 30 minutes a complicated mixture of sugars was obtained.…”

mentioning

confidence: 99%

Investigations of Ring-Opening Reactions of Cyclopropanated Carbohydrates: Towards the Synthesis of the Natural Product (--)-TAN-2483B

Hewitt¹

View full text Add to dashboard Cite

<p>Cyclopropanes and carbohydrates are materials of great interest to chemists. Ring opening reactions of cyclopropanated carbohydrates have excellent potential for synthesis, due to the many diverse structures that may be obtained. The work described in this thesis explores the scope of such ring opening reactions, and extends to the synthesis and reactions of several novel cyclopropanated carbohydrates, in which synthesis of a natural product was also investigated. Several bicyclic gem-dihalocyclopropanes, including 97, were synthesised. Base-mediated cyclopropane ring opening of 97 in the presence of nucleophiles afforded a series of 2-C-branched glycosides 389 and 390 (Chapter 2), whereas silver-promoted ring expansion provided access to seven-membered rings (255 and 256) (Chapter 3). Studies on the mechanisms of the ring opening processes were also carried out. Ring-opening reactions of carbohydrate-derived gem-dihalocyclopropanes were also applied to the exploration of possible routes to the natural product (--)-TAN-2483B (154). Attempts to convert d-galactose and d-xylose into the dihydropyran 193 are the subject of Chapter 4, while the transformation of d-mannose into 193 and subsequent efforts to prepare the natural product 154 are discussed in Chapter 5.</p>

show abstract

mentioning

confidence: 99%

Investigations of Ring-Opening Reactions of Cyclopropanated Carbohydrates: Towards the Synthesis of the Natural Product (--)-TAN-2483B

Hewitt¹

View full text Add to dashboard Cite

show abstract

Transformation of Glycals into 2,3‐Unsaturated Glycosyl Derivatives

Ferrier

Zubkov

2003

Organic Reactions

View full text Add to dashboard Cite

Various elimination procedures conducted on appropriate pyranoid and furanoid carbohydrate derivatives, especially on O ‐protected glycosyl halides afford cyclic vinyl ethers which Fischer (inappropriately) named glycals. These are used extensively in general organic synthesis and for the preparation of non‐carbohydrate natural products as well as biologically important complex carbohydrates and glycoconjugates. The best known member, tri‐ O ‐acetyl‐D‐glucal, is normally made from tetra‐ O ‐acetyl‐alpha‐D‐glucopyranosyl bromide, is commercially available, and is used very frequently in this chapter to represent the family in examples of the reactions under discussion. Because of the pronounced region‐ and stereoselectivities with which their addition reactions can be conducted, glycal derivatives are of major importance in synthesis. They also, however, take part in rearrangement processes that, likewise, have proved useful for synthesis. The principal one involves nucleophilic substitution of the allylic group with allylic rearrangement and results in products having double bonds in the 2, 3 positions and new substituents at the anomeric centers. By far the simplest and most commonly used way to this conversion involves the removal of the allylic substituent of the glycal and the generation of highly resonance‐stabilized oxocarbenium ion intermediate. This may then react with nucleophiles at the anomeric center to give products as mixtures of diastereomers. Many examples and variations of this theme are described and form the major part of this chapter, but other ways are also considered Almost no formal mechanistic studies have been carried out on the reactions in this chapter. Categorization of mechanism required for the treatment of this topic has been done on the basis of conditions used, product identification and largely, chemical intuition.

show abstract