Synthesis and reactions of fluorinated organic peroxides have been reviewed. Fluorinated organic peroxides are discussed in the following sections : (I) Synthesis and reactions of fluorinated diacyl peroxides, (II) Synthesis and reactions of fluorinated dialkyl peroxides, (III) Synthesis and reactions of fluorinated percarboxylic acids and hydroperoxides, (IV) Synthesis and reactions of fluorinated peroxy esters.
Direct asymmetric syntheses involve enantioselective reactions with diastereo- or enantiodifferentiation. Among enantioselective reactions will be discussed two selected topics on utilization of chiral leaving groups and on asymmetric protonations.
Using carbohydrates as chiral synthons, a synthesis of enantiomers of natural products and their analogs has been widely studied. Recently, in our laboratory, (-) -swainsonine and its two congeners have been successfully synthesized from D-glucose and (+) -pseudoconhydrine from D-glucosamine, as well as two pseudo-sugars from L-arabinose and methyl (-) -shikimate from D-lyxose. These chiral synthetic processes have been summarized in the present article.
Synthetic studies on biologically active and structurally unique unusual amino acids, isolated as a free form or a constituent of peptides, have been described. (1) The synthesis of neurotoxin, (-) -domoic acid (3) was achieved starting from L-glutamic acid via a stereospecific [4 + 2] cycloaddition of 5 followed by a construction of the C-1' side chain. (2) Optically pure 2-amino-3-butenol (15), prepared from L-or D-methionine, was used as the chiral serine equivalent as well as a building block for the syntesis of β-hydroxy-α-amino acid system. This was converted to the aspergillomarasmine A skeleton 24 and galantinic acid (28). (3) Significant 1, 2- and 1, 3-asymmetric induction of 2-amino-4-pentenoic acid system 17 (allylglycine) has been observed during the introduction of a hydroxyl group into its unsaturated side chain. For example, allylic oxidation of 35 provided the threo-β-hydroxyallylglycine derivative 36 as the major product, and halolactonization of 61 afforded the cis bromolactone 62, predominantly. These intermediates were efficiently transformed to the hydroxyproline analogues 40, 71, and 72. On the other hand, cyclopropylglycines (58) and (59) have been synthesized from the β-hydroxy-allylglycine derivative via a Pd (II) catalyzed [3, 3] sigmatropic rearrangement and a subsequent cyclopropanation. In addition, several useful transformations concerning amino protecting groups were also disclosed.
Iodosylbenzene activated by the coordination of Lewis acids to the oxygen atom reacts readily with a variety of organosilicon and tin compounds to produce the hypervalent organoiodine (III) species. Allyl- and vinyliodine (III) compounds are highly reactive and act as the species equivalent to allyl and vinyl cations, because iodine (III) at the hypervalent state is a good Ieaving group. Reaction of alkynyliodine (III) compounds with stable enolates of 1, 3-dicarbonyl compounds produces substituted cyclopentenes via the (1, 5) C-H insertion of alkylidene carbene intermediates. 1, 4-Fragmentation of γ-tributylstannyl alcohols using iodosylbenzene, BF3, and DCC gives rise to unsaturated carbonyl compounds. The fragmentation, combined with conjugated addition of Bu3SnLi and reduction or alkylation, offers an efficient procedure for the reductive and alkylative ring opening of cyclic vinyl ketones.
Marine organisms produce toxic substances of unique nature in both chemical structure and biological activitiy, because the ocean provides a diversity of fauna and flora. Toxins which have been isolated from blue-green algae, dinoflagellates and macroalgae include aplysiatoxins, okadaic acid and related toxins, saxitoxin and its derivatives, brevetoxins, and ichthyotoxic terpenes. Sponges contain a variety of ichthyotoxic terpenes and latrunculins, while coelenterate toxins compose of palytoxins, ichthyotoxic terpenes and glycosides, and neurologic peptides. Mollusks possess a variety of toxic substances ranging from alkaloids, terpenes to neurologic peptides. Glycosides and peptidic toxins are produced by either echimoderms, fishes or nemertines.