Ketones caution with

B. a,a -Dibromodineopentyl Ketone. Caution The dibromoketone, a highly volatile compound with lachrymatory properties, is a skin irritant which may induce allergic effects. Therefore, steps B and C should be performed in a well-ventilated hood. Rubber gloves should be worn. 

Nitropropane (17.8g 0.2mol) and diisopropylamine (10ml) in 200ml of chloroform are stirred at 60 °C under a nitrogen atmosphere. Methyl vinyl ketone (CAUTION) (7 g, 0.1 mol) is added dropwise to this solution. After 3 hours another portion of methyl vinyl ketone (7 g, 0.1 mol) is added and the solution stirred for 24 hours. The solution is washed sequentially with water, 10 per cent aqueous hydrochloric acid, 5 per cent sodium hydrogen carbon-... 

Diethyl pyrocarbonate (DEP) [1609-47-8] M 162.1, b 38-40°/12mm, 160-163 /atm, d 1.119, Op 1.398. Dissolve in Et20, wash with dilute HCl, H2O, dry over Na2S04. filter, evaporate and distil the residue first in vacuo then at atmospheric pressure. It is soluble in alcohols, esters, ketones and hydrocarbon solvents. A 50% w/w soln is usually prepared for general use. Treat with great CAUTION as DEP irritates the eyes, mucous membranes and skin. [Boehm and Mehta Chem Ber 71 1797 1938 Thoma and Rinke Justus Liebigs Ann Chem 624 30 1959.]... 

The effect of an a-substituted oxirane group on the optical rotatory dispersion of steroidal ketones should be interpreted with caution an inverted octant rule for a-epoxy ketones has been proposed/although recent data indicate that the normal octant rule may still be valid. 

Reaction with alcohols is general for diazo compounds, but it is most often performed with diazomethane to produce methyl ethers or with diazo ketones to produce ot-keto ethers, since these kinds of diazo compounds are most readily available. With diazomethane the method is expensive and requires great caution. It is used chiefly to methylate alcohols and phenols that are expensive or available in small amounts, since the conditions are mild and high yields are obtained. Hydroxy compounds react better as their acidity increases ordinary alcohols do not react at... 

Dauben et al. (15) applied the Aratani catalyst to intramolecular cyclopropanation reactions. Diazoketoesters were poor substrates for this catalyst, conferring little asymmetric induction to the product, Eq. 10. Better results were found using diazo ketones (34). The product cyclopropane was formed in selectivities as high as 77% ee (35a, n = 1). A reversal in the absolute sense of induction was noted upon cyclopropanation of the homologous substrate 34b (n = 2) using this catalyst, Eq. 11. Dauben notes that the reaction does not proceed at low temperature, as expected for a Cu(II) precatalyst, but that thermal activation of the catalyst results in lower selectivities (44% ee, 80°C, PhH, 35a, n = 1). Complex ent-11 may be activated at ambient temperature by reduction with 0.25 equiv (to catalyst) DIBAL-H, affording the optimized selectivities in this reaction. The active species in these reactions is presumably the aluminum alkoxide (33). Dauben cautions that this catalyst slowly decomposes under these conditions. 

Phosphonamidate peptide analogues mimicking the P1...F3 substrate residues have been prepared and evaluated against a CHC mixture Table 8.5). Inhibitors with an aromatic side-chain in subsite P] are some 20-fold more effective than are those with an aliphatic one (compare (31) to (29) or (30), Table 8.S). An opposite, albeit less pronounced, preference at this site appears to exist for the ketone inhibitors for fi-CYlC ((17) vs. (25) and (21) vs. (26), Table 8.4). However, this difference could be attributable to a predominance of class II CHC in the mixture assayed in Table 8.5. Thus, comparisons of this sort must be made with caution. Introduction of a double bond into the Pi side-chain decreases the potency of the phosphonamidate by more than a factor of 10 ((41) vs. (42), Table 8.5), perhaps because of... 

Caution. Carbon monoxide is an odorless, extremely toxic gas and must be handled in an efficient hood. Solid Cu(CO)Cl exhibits a very high CO dissociation pressure and should be handled with the same care as carbon monoxide. Ethyl vinyl ketone (EVK) is a strong lachrymator and must be handled in a well-ventilated hood. EVK may contain peroxides and caution must be exercised when distilling. 

Starting with ketones and hydrogen peroxide in the presence of a catalytic amount of acid, mixtures of up to eight components have been identified, i.e.. (1, X = OH. R3 = H), (1, X = OOH, R3 = H), (2, X = Y = OH). (2, X = Y = OOH), (2, Y = OH, Y = OOH), (3). (4), and (5). The ketone structure and reaction conditions, i.e., acid strength, reactant molar ratios, temperature, and time, determine which compounds form and predominate. Mixtures of several peroxide structures usually are present. Individual peroxides have been isolated from several ketones under different conditions (Table 5). The pure peroxides should be handled with extreme caution since most, especially those derived from the low moleculai weight ketones, ate shock- and friction-sensitive and can explode violently. Methyl ethyl ketone peroxide (MEKP) mixtures are produced commercially only as solutions containing <40 wt% MEKPs in solvents, commonly dialkyl phthalates. 

Lithium borohydride is intermediate in activity as a reducing agent between lithium aluminium hydride and sodium borohydride. In addition to the reduction of aldehydes and ketones it will readily reduce esters to alcohols. It can be prepared in situ by the addition of an equivalent quantity of lithium chloride to a 1m solution of sodium borohydride in diglyme. Lithium borohydride should be handled with as much caution as lithium aluminum hydride. It may react rapidly and violently with water contact with skin and clothing should be avoided. 

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