2.1.8. Michael Reaction 2245 2.1.9. Others 2247 2.2. Cyclization Reactions 2248 2.2.1. Carbon Diels−Alder Reactions 2248 2.2.2. Aza-Diels−Alder Reactions 2252 2.2.3. Other Hetero-Diels−Alder Reactions 2255 2.2.4. Ionic Diels−Alder Reaction 2256 2.2.5. 1,3-Dipolar Cycloadditions 2256 2.2.6. Other Cycloaddition Reactions 2258 2.2.7. Prins-type Cyclization 2259 2.3. Friedel−Crafts Acylation and Alkylation 2259 2.4. Baylis−Hillman Reaction 2263 2.5. Radical Addition 2264 2.6. Heterocycle Synthesis 2267 2.7. Diazocarbonyl Insertion 2270 3. C−X (X ) N, O, P, Etc.) Bond Formation 2271 3.1. Aromatic Nitration and Sulfonylation 2271 3.2. Michael Reaction 2272 3.3. Glycosylation 2273 3.4. Aziridination 2275 3.5. Diazocarbonyl Insertion 2276 3.6. Ring-Opening Reactions 2277 3.7. Other C−X Bond Formations 2280 4. Oxidation and Reduction 2280 4.1. Oxidation 2280 4.2. Reduction 2281 5. Rearrangement 2283 6. Protection and Deprotection 2285 6.1. Protection 2285 6.2. Deprotection 2288 7. Polymerization 2291 8. Miscellaneous Reactions 2291 9. Lanthanide(II) Triflates in Organic Synthesis 2295 10. Conclusion 2295 11. Acknowledgment 2295 12. References 2295

Rare-earth metal triflates in organic synthesis

Glycals (or usually their O-substituted derivatives) are readily converted into 2,3-unsaturated glycosyl compounds with O-, C-, N-, S- or otherwise linked substituents at the anomeric position. These products have been found to be useful for a range of synthetic purposes. In particular, the C-glycosidic compounds have served as readily available starting materials for the preparation of useful non-carbohydrate compounds. While these allylic rearrangement processes are usually conducted under the influence of Lewis acid catalysts, adaptations that involve activation of the allylic substituents of the starting glycals as leaving groups under neutral conditions have been developed. General features of the reactions are described as well as applications in synthesis and extensions of the basic processes.

Substitution-with-Allylic-Rearrangement Reactions of Glycal Derivatives

Some Progeny of 2,3-Unsaturated SugarsThey Little Resemble Grandfather Glucose: Twenty Years Later,1

Perchloric acid supported on silica gel acts as an excellent reagent system in converting glucals into 2,3-unsaturated-O-glucosides in good to excellent yields in short reaction time with good a selectivity. Primary, secondary, and allylic alcohols, phenols, and thiols react with 3,4,6-tri-O-acetyl glucal with equal ease. In addition to this, a chiral furan diol is obtained from unprotected D-glucal or D-galactal in good yields.

Protic acid (HClO4 supported on silica gel)-mediated synthesis of 2,3-unsaturated-O-glucosides and a chiral furan diol from 2,3-glycals.

Publisher Summary The United States National Cancer Institute (NCI) has recently intensified its emphasis upon natural products as a source of new drug discovery. This chapter deals with the antitumor and antiviral substances derived from fungi. The fungi produce many antibiotic substances besides penicillin, some of which have been reported to show antiviral or antitumor activity. The metabolic pathways of fungi can be divided into two broad areas: the primary metabolism that provides the fungi with energy, synthetic intermediates and key macromolecules, such as protein and DNA; and the secondary metabolism that yields a range of species-specific compounds possessing no obvious function in cell growth. The discovery of novel substances with anticancer and antiviral activities from fungi are extensive, yet the more systematic and successful exploration of fungi for potentially useful new anticancer and antiviral drugs has undoubtedly been constrained by limitations in available screening systems. Therefore, the NCI has also more recently assumed responsibilities for the implementation of a national acquired immunodeficiency syndrome (AIDS) antiviral drug screening and drug development program in parallel and in complement to the anticancer drug program.

Antitumor and antiviral substances from fungi.

Catalysis by mercuric ion of reactions of glycals with water

Some stereochemistry of 'asperlin' (1) and related fungal metabolites containing a 5,6-dihydro-2-pyrone moiety, has been deduced through correlation of nmr and ord parameters with those of reference compounds derived from carbohydrates of known stereochemistry. The reference compounds are 4,6-di-O-acetyl-2,3-dideoxy-D-threo- and -D-erythro-hex-2-enono-1,5-lactones obtained by modification of D-galactal and D-glucal, respectively, and the D-enantiomer of 1, synthesized in a multistep sequence from D-galactose. It is shown that the 5,6-substituents of the pyrone ring of 1 have the L-threo configuration and also that the exocyclic epoxypropyl moiety is trans.

Synthesis and stereochemistry of 2-pyrone derivatives related to some fungal metabolites

13C nmr data indicate that the epoxypropyl side chain of 'asperlin' (1) has a trans configuration. This assignment follows from associated measurements on model compounds, showing that the 13C chemical shift of an epoxypropyl CH3 group is close to either 17 ppm (trans isomers) or 13 ppm (cis isomers). Synthesized as oxirane derivatives related to 1 are diastereomeric pairs of 8-deoxy-6,7-cis- and -trans-epoxy-1,2:3,4-di-O-isopropylidene-α-D-galacto-octopyranoses.

Suzanne Lesage

Papers

Catalysis by mercuric ion of reactions of glycals with water

Synthesis and stereochemistry of 2-pyrone derivatives related to some fungal metabolites

13C-nuclear magnetic resonance spectra of oxiranes. Configuration of 1,2-epoxypropyl side chains in fungal metabolites

Synthesis and stereochemistry of 2‐pyrone derivatives related to some fungal metabolites