Lead acetate in preparation of selective

Lauraldehyde, 46, 36 Lead acetate in preparation of selective palladium catalyst, 46, 90... 

Lauraldehyde, 46, 36 Lead acetate in preparation of selective palladium catalyst, 46,90 Lead tetraacetate, assay for, 46, S3 in functionalization of C-19 methyl group of 3/S-acetoxy-20 S-hy droxy-5-pregnene, 46, 58... 

Various kinds of chiral acyclic nitrones have been devised, and they have been used extensively in 1,3-dipolar cycloaddition reactions, which are documented in recent reviews.63 Typical chiral acyclic nitrones that have been used in asymmetric cycloadditions are illustrated in Scheme 8.15. Several recent applications of these chiral nitrones to organic synthesis are presented here. For example, the addition of the sodium enolate of methyl acetate to IV-benzyl nitrone derived from D-glyceraldehyde affords the 3-substituted isoxazolin-5-one with a high syn selectivity. Further elaboration leads to the preparation of the isoxazolidine nucleoside analog in enantiomerically pure form (Eq. 8.52).78... 

Citronellal, an aldehyde with a trisubstituted double bond, was hydrogenated to citronellol over a ruthenium catalyst poisoned with lead acetate in 90-100% yields (eq. 5.22)46 or over chromium-promoted Raney Ni in 94% yield in methanol at 75°C and about 0.31 MPa H2.47 Court et al. studied the selective hydrogenation of citral (1, eq. 5.24) to citronellol over unsupported Nij. o catalysts, prepared by reduction of mixtures of metal iodides with naphthalene-sodium as reducing agent, in cyclohexane and in 2-propanol at 80°C and 1.0 MPa H2.48 Higher yields of citronellol were obtained in 2-propanol than in cyclohexane, primarily via citronellal as the predominant intermediate. The yields of citronellol for the overall hydrogenation in 2-propanol over Mo-promoted catalysts were Mo0 03 96%, Mo0 06 98%, and Mo012 96%. 

Another aspect of tin as a constituent of electrode material is shown by tin(IV)TPP complexes incorporated into PVC membrane electrodes. These increase the selectivity to salicylate over anions such as Cl-, Br- I-, I()4, Cl()4, citrate, lactate and acetate. The specificity is attributed to the oxophilic character of the Sn ion in TPP at the axial coordination sites. Indeed, carboxyl groups incorporated into the membrane polymer compete for these binding sites. The complete complex structure is important. Substitution of TPP with octaethylporphirine results in loss of salicylate selectivity231. Preparation and analytical evaluation of a lead-selective membrane electrode, containing lead diethyldithiocarbamate chelate, has also been described232. 

Lead tetraacetate is used as a highly selective oxidizing agent in organic synthesis. This includes oxidation of glycols into aldehydes, preparation of cyclohexyl acetate, production of oxahc acid, and in structural analysis of sugars. 

The use of activated anthranihc acid derivatives facUitates the preparation of the amides in those cases where the amines are either umeactive or difficult to obtain. Thus, reaction of (87-1) with phosgene gives the reactive the isatoic anhydride (89-1). Condensation of that with ortho-toluidine leads to the acylation product (89-2) formed with a simultaneous loss of carbon dioxide. This is then converted to the quinazolone (89-3) by heating with acetic anhydride. Reaction with sodium borohydride in the presence of aluminum chloride selectively reduces the double bond to yield the diuretic agent metolazone (89-4) [99]. 

The key sequence in a somewhat involved stereospecihc total synthesis of a carbacephem starts by preparation of a chiral auxiliary. It is interesting to note that nitrogen is the only atom from this molecule retained in the hnal product. Constmction of this moiety starts with the formation of the carbethoxy derivative (37-2) from L(- -)-phenylglycine (37-1). Selective reduction of the free carboxyl group with borane. THF leads to the hydroxycarbamate (37-3). In a one-pot sequence, this is first cyclized to the corresponding oxazolidinone (37-4) by means of sodium hydride and then alkylated with ethyl bromoacetate (37-5). Saponification of the side chain then affords the chiral acetic acid (37-6). The carboxyl group is then activated by conversion to its acid chloride (37-7). 

Cyclic voltammetry provided Yudin with information that oxidation of aminophthalimide at +1.8 V will provide an active nitrogen species capable of aziridinating both electron-rich and electron-poor olefins. The electron-rich olefin of the diene 33 was thus able to be selectively aziridinated to provide aziridine 34 (Equation 15) <2005JOC932>. Yudin found that addition of acetate anion was key in the aziridination process. Addition of acetate to the solution forms the A -acetoxyaminophthalimide, a compound previously prepared by oxidation of aminophthalimide with lead tetraacetate. The absence of acetate allows the aminophthalimide to dimerize, then oxidize further to lose nitrogen and provide phthalimide as the final product, without any reasonable concentration of aziridinating agent. 

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