Silyl ketene acetals (SKA) have attracted much attention as useful synthetic reagents. This review deals with the recent studies (mainly after 1980) on the preparations and reactions utilizing SKA in the following items with 147 references;  Preparations; a) general preparation, b) selective synthesis of E- and Z- SKA.  Reactions; a) protonation, b) oxidation, c) electrophilic substitution, d) cycldaddition, e) sigmatropic reaction, f) others.
2, 2, 6, 6, -Tetramethylpiperidine-1-oxyl known as a stable radical is reduced to the hydroxylamine and is also oxidized to the oxoaminium salt. These redox reactions are reversible chemically. In this article we describe some application of nitroxyl radical to organic reactions based on its redox function. Hydroxylamine was demonstrated to work as a hydration reagent of nitriles to produce amides. Further, it was found that oxygen is reduced by an anion of hydroxylamine to give superoxide ion. Oxoaminium salt, an oxidized form of nitroxyl radical, oxidized hydroxide ion and alcohols to give selectively hydrogen peroxide and the corresponding carbonyl compounds, respectively. The redox systems using oxoaminium salt as a mediator were investigated. Further, we found that the polymeric mediator was superior to the monomeric mediator.
The synthetic target marine natural product, okadaic acid, with 38 carbon back-bone and 17 asymmetric centers was retro-synthesized into three segment A, B and C. First, segments C was synthesized from a D-glucose derivative by heteroconjugate addition as the key step to generate sym-diastereo relationship by α-chelation control through the Spiro ethereal oxygens. The segment B was synthesized from a D-glucal and coupled with segment C. Segment A containing anti-diastereo isomerism was prepared from the same sugar as for segment C and several new methods were developed to solve the problems on the stereoselection and coupling the segments. The total synthesis of okadaic acid was concluded in about 100 steps. A general rule in the acyclic stereoselection was established through this study ; that is to distinguish the sp2 faces effected by the neighbouring substituents.
Substituent effects observed in VUV photoelectron and UV absorption spectra may provide us with information concering π-orbital levels and ππ* transition energies, in other words, mesomeric effects. On the other hand, the inductive effect on the harmonicity can be evaluated by employing overtone spectroscopy of X-H bonds (X = C, N, and O). Since these spectral data are complementary, a combination of spectroscopic methods is suitable for describing total substituent effects. The interpretation of observed substituent effects can be properly made on the basis of molecular orbital approximation without making use of Hammett σ values.
Bis (p-methoxyphenyl) selenoxide, readily available from anisole and selenium dioxide or selenium oxychloride, is of practical use as a tractable and versatile oxidizing agent. Thus it can be used for mild oxidations of thiol to disulfide, sulfide to sulfoxide, hydroquinone to p-benzoquinone, catechol to o-benzoquinone, phosphine to phoshine oxide, benzoylhydrazine to sym- dibenzoylhydrazine, phenylhydroxylamine to azoxybenzene, and benzoin to benzil. Its specific reactivity is demonstrated by a useful conversion of thioamides involving thioureas into 1, 2, 4-thiadiazoles. In particular, polymer-supported analogous selenoxide effects novel solvent-dependent reactions toward thioamides. In addition, the title selenoxide has potential applicability such as an effective reagent for Kornblum reaction, a cooxidant for catalytic SeO2 oxidation, and a mediator for electrochemical oxidation.
Symmetric oxalates containing N-hydroxyimide or N-hydroxybenzotriazole group easily prepared from oxalyl chloride and N-hydroxyimide or N-hydroxybenzotriazole, are employed for the synthesizing of activated ester from corresponding N-protected amino acid. The active esters containing N-hydroxyimide or N-hydroxybenzotriazole derivatives react smoothly with nucleophiles such as amino acid to afford the corresponding dipeptides in high yields. In particular, N, N'-disuccinimidyl oxalate (DSO) is the most useful and easily handle reagent even in the synthesis of dipeptide of free carboxylic acid. In order to evaluate the local irritability of DSO, the eye and skin irritation tests were investigated with rabbit using DCC as a control substance. As shown in Table 1, 2 and Fig. 1 the local irritability of DSO was clearly weaker than that of DCC.