Cesium carbonyl compounds

Azomethine ylides undergo a formal [3 + 2] cycloaddition with carbonyl compounds to provide oxazolines. Thioimidates, in particular, are effective as ylide precursors. For example, Kohra and co-workers reported that the thioimidate 260, upon activation with cesium fluoride, reacts with aromatic aldehydes and diaryl-ketones to provide oxazolines 261 in modest to good yields. Aliphatic aldehydes and simple ketones are unreactive (Scheme 8.72). 

The reaction affords triphenylsilylrubidium and -cesium, via the disilane, in situ [4]. Trifurylgermane adds to a,/ -unsaturated carbonyl compounds in the presence of catalytic amount of cesium carbonate (Scheme 2.2) [5]. The Ge-H bond in trifurylgermane releases a proton to form the Ge-Cs compound. 

Carbanion equivalents with anion stabihzing groups are prepared by desilylation of the corresponding materials with cesium fluoride [9-15]. In Scheme 2.6 treatment of aryltrimethylsilanes with cesium fluoride affords carbanion equivalents which add to the carbonyl compounds. The reactive species are not simple organocesium compounds but react as nucleophilic carbanion equivalents. 

Alkynylation. This base (monohydrate) is an excellent catalyst for alkynylation of carbonyl compounds and selective A-monoalkylation of primary amines.- Cesium hydroxide suppresses overalkylation, and therefore is very useful in the exclusive formation of secondary amines from amino acids. 

One class of reaction evidently missing from this list is the reaction of sulfenes with electrophiles. Sulfene itself is strongly electrophilic and this class may be expected to be small. One class of reaction formally involving a sulfene and an electrophile is the cycloaddition with chloral and related carbonyl compounds. Evidence has been obtained for the importance of tertiary amines in this process and, as is discussed in Section V.B.5, it is unlikely that it is a simple reaction of a sulfene with an electrophile. The reaction of (trimethylsilyl)methanesulfonyl chloride with cesium fluoride in the presence of bromine... 

Commercial potassium fluoride (dehydration not necessary) (50 mmol), or finely powdered commercial cesium fluoride (20 mmol) is stirred with dialkyl H-phosphonate (10 mmol) and the carbonyl compound (10 mmol) at room temperature for a period of 0.5 to 1 h. The reaction mixture is extracted with dichloromethane (50 mL) by shaking for... 

The results of allylation of various aldehydes with allyltrifluorosilanes and cesium fluoride are shown in Table VI. The allylation was regiospecific where the carbon-carbon bond formation occurred exclusively at the 7-carbon of aUylsilanes. No other regio-isomers were detected in all the cases. Although aUylation of carbonyl compounds with aUylsilanes and Lewis acids has been well established as a procedure for the regiospecific preparation of homoallyl alcohols by our previous studies, yields are often lowered by the undesired side reactions. Advantageously, the present aUylation can be carried out under very mUd and neutral conditions affording the homoallyl alcohols in exceUent yields. 

Reduction of Functional Groups Catalyzed by Fluoride or Alkoxide Salts. A general and powerful reduction method of carbonyl compounds consists of using HSi(OEt)3 activated by potassium fluoride or cesium fluoride. The reaction can proceed without solvent (eq 3) and is accelerated by polar solvents, e.g. DMSO or DMF The reduction of aldehydes and ketones is rapid at room temperature also, esters are smoothly converted to alcohols (eq 4). ... 

The compound K2 [Rh6(CO)15C] is a yellow powder. It is sensitive to air both in the solid state and in solution and is quite soluble in water, methanol, ethanol, acetone, THF, and acetonitrile. The salts of other cations can be obtained by metathesis, in water for the cesium salt and in methanol for the larger tetra-alkylammonium or phosphonium cations. The tetraethylammonium salt is sparingly soluble in THF, whereas the benzyltrimethylammonium and bis-(triphenylphosphine)imminium salts are soluble. All of these salts are soluble in acetone and acetonitrile. The yellow solution of the potassium salt in THF shows characteristic IR bands at 2040 (vw), 1990 (vs), 1885 (vw), 1845 (s), 1830 (sh, m) 1815 (sh, br) and 1775 (vw, br) cm-1. The IR spectral band shapes depend on solvents and cations. The oxidation of K2 [Rh6(CO)i5C] with iron-(III) ammonium sulfate in water under carbon monoxide leads to the octa-nuclear carbido carbonyl cluster Rhg(CO)i9C,6 whereas under nitrogen RhntCO sQ7 or [H30] [Rhls(CO)28C2]8 is obtained. 

John specialized in fluorine, boron, sulfur, phosphorus, and metal carbonyl chemistry. With M. Frederick Hawthorne, he discovered a series of amine complexes of aluminum trihydride and showed that some of them give aluminum metal when heated this process later became useful for the formation of aluminum thin films by chemical vapor deposition. One of his notable achievements was the discovery that the PPN cation, bisftriphenylphosphoranyhdene) ammonium, forms air-stable salts with many air-sensitive anions such as [Co(CO)4] . He also discovered that cesium fluoride can serve as a catalyst for the synthesis of organic fluoroxy compounds (RpOF) by the fluorination of acyl halides. 

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